System UI crashes while requesting USB access permission using USB host api

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• Android MediaPlayer files path not found

  I'm new in android development trying to play a simple audio file. I organized my audio files in multiple nested folders.

  Here is the complete source on disk "app/src/main/res/raw/sounds/first/nested/my_sound_1.mp3" ... Certainly there are other files in different folders.

  This is the method I'm using to play the audio file

  fun audioPlayer(path : String, fileName: String) {
  
     var mediaPlayer = MediaPlayer()
  
      try {
          mediaPlayer.setDataSource(path + File.separator + fileName)
          mediaPlayer.prepare()
          mediaPlayer.start()
  
      } catch (e: Exception) {
          e.printStackTrace()
      }
  
  }
  

  and on a button click event I'm using this code

  audioPlayer("raw.sounds.first.nested", "my_sound_1.mp3")
  

  Here is the error.

  java.io.IOException: setDataSource failed.
  
• Android listview item click effecting on multiple items

  I have a product list. I can set order quantity for per item. For this, I have used dialog and item position. But when I'm putting quantity for a single item it affecting in multiple items.

  Problem Video I have used bellow code

  sListview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
      @Override
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
  
          final Dialog dialog = new Dialog(OrderEntryActivity.this);
          dialog.setContentView(R.layout.order_qty_collect);
  
  
          TextView tvpid= (TextView) view.findViewById(R.id.pId);
          TextView tVpid= (TextView) dialog.findViewById(R.id.pcode);
          PRODUCTID=tvpid.getText().toString();
          tVpid.setText(PRODUCTID);
  
          final TextView parentitemid= (TextView) dialog.findViewById(R.id.parentitemid);
          parentitemid.setText( String.valueOf(position));
  
          TextView tvpname= (TextView) view.findViewById(R.id.pName);
          TextView tVpname= (TextView) dialog.findViewById(R.id.pName);
          tVpname.setText(tvpname.getText());
  
          TextView tvpprice= (TextView) view.findViewById(R.id.pPrice);
          TextView tVpprice= (TextView) dialog.findViewById(R.id.pPrice);
          TextView pQty= (TextView) dialog.findViewById(R.id.poQty);
          tVpprice.setText(tvpprice.getText());
          dialog.setCancelable(false);
          dialog.show();
  
          Button submit = (Button) dialog.findViewById(R.id.btn_qtySubmit);
  
          submit.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  TextView PIid= (TextView) dialog.findViewById(R.id.parentitemid);
                  int ItemPogision =Integer.parseInt(PIid.getText().toString());
  
                  EditText qTy= (EditText) dialog.findViewById(R.id.qtyId);
                  String qtY=qTy.getText().toString();
                  if(qtY.equals("")){
                      Toast.makeText(OrderEntryActivity.this,"Order Quantity Blank. Please fillup.",Toast.LENGTH_SHORT).show();
                  }else{
                      Integer Qty= Integer.parseInt(qtY);
                      salesDB.deleteTmpOrderByPID(PRODUCTID);
                    Boolean x=salesDB.TmpOrderInsert(CUSTID,PRODUCTID,Qty);
                    if(x==true){
                        TextView pqty= (TextView) sListview.getChildAt(ItemPogision).findViewById(R.id.poQty);
                        pqty.setText(qtY);
                        sListview.getChildAt(ItemPogision).setBackgroundColor(Color.GREEN);
  
                        Toast.makeText(OrderEntryActivity.this,"Added to Cart",Toast.LENGTH_SHORT).show();
                        dialog.dismiss();
                        Count++;
                        count.setText(Count.toString());
                    }else{
                        Toast.makeText(OrderEntryActivity.this,"Fail to add into Cart",Toast.LENGTH_SHORT).show();
                    }
  
                  }
              }
          });
  
          Button close = (Button) dialog.findViewById(R.id.btn_cancel);
          close.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  dialog.cancel();
              }
          });
      }
  });
  

  In the video you can see that, there I have put order quantity for two product but it affecting multiple products from the item list.
• Closed variable anulled in Rx callback

  My understanding is that in the following code variable context should never be null.

  But, when debugger is attached, variable context is frequently null when lambda is executed.

  This behavior is reproducible three out of five times.

  How can that be explained?

  object MyOtherService {
    fun start(context:Context){
      Log.d("", context != null) // always true
  
      SlowServiceObserver
        .getObservable()
        .observeOn(Schedulers.computation())
        .subscribe({
          Log.d("", context != null) // sometimes false
        })
    }
  }
  
  public class MyApp extends Application {
  
    public void onCreate(){
      super.onCreate();
  
      MyService.INSTANCE.start(this);
  
      SlowService slowService = new SlowService();
      SlowServiceObserver.INSTANCE.notify(slowService);
    }    
  }
  
  object SlowServiceObserver {
  
    private val mBehaviorSubject : BehaviorSubject<BehaviorSubject> = BehaviorSubject.create()
  
    fun getObservable(){
      return mBehaviorSubject
    }
  
    fun notify(instance: SlowService){
       mBehaviorSubject.onNext(instance)
    }
  }
  

  Can it be that Kotlin object somehow changes the closure? Or is this some expected behavior in RxJava?
• Padding not working in my Button

  In my Button I have this XML:

   <Button
      android:id="@+id/btnFiltrarResultados"
      android:layout_width="18dp"
      android:layout_height="17dp"
      android:layout_above="@+id/searchView"
      android:layout_alignParentEnd="true"
      android:layout_marginBottom="-37dp"
      android:layout_marginEnd="29dp"
      android:background="@drawable/filtrar_explorar"
      android:cropToPadding="true"
      android:padding="20dp"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toEndOf="@+id/txtExploreTitulo"
      app:layout_constraintTop_toTopOf="parent"
      app:layout_constraintVertical_bias="0.01999998" />
  

  But I can't seem to be able to add padding to it. I've tried using cropToPadding or using android:src but nothing seems to help...
• ViewPager Imageview is showing issue

  I am using imageview inside the viewpager and i want to show the image centerInside the image view but its not showing in a good view. Imageview provides in the left and right side of imageView blank space. But in some cases its shows good view.

  This is my viewpagerAdapter

  private class ImagePagerAdapter extends PagerAdapter {
      public ImagePagerAdapter(){
      }
  
      @Override
      public int getCount() {
          if(visibleImagesCount==0){
              return 1;
          }
          return visibleImagesCount;
      }
  
      @Override
      public int getItemPosition(Object object) {
          return POSITION_NONE;
      }
  
      @Override
      public boolean isViewFromObject(View view, Object object) {
          return view == object;
      }
  
      @Override
      public void destroyItem(ViewGroup container, int position, Object object) {
          container.removeView((RelativeLayout) object);
      }
  
      /**
       * Following method is responsible to load images into ViewPager
       * @param container
       * @param position
       * @return
       */
      @Override
      public Object instantiateItem(ViewGroup container, int position) {
  
          final Context context = getActivity();
  
  
  LayoutInflater inflater = (LayoutInflater) getActivity()
                  .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
          RelativeLayout relativeLayout= (RelativeLayout) inflater.inflate(R.layout.view_pager_fragment,null);
  
          final ImageView imageView= (ImageView)relativeLayout.findViewById(R.id.view_pager_image_view_show);
  
          RequestManager glide=Glide.with(getContext());
          {
  
                  List<Image> list = dbHelper.getAllVisibleImagesList();
  
  
                  Image image = list.get(position);
  
                  final String filePath = Constants.Path.IMAGE_LOADING_PATH + imageName;
                  Bitmap bitmap;
                  if(image.getImageStatus() != ImagesStatus.STATUS_IMAGE_ADDED.getStatus())
                      bitmap = ImageUtils.getBitmap(thumbURL);
                  else
                      bitmap= BitmapFactory.decodeResource(context.getResources(), R.drawable.black_image);
  
                  Drawable d = null;
                  if(bitmap != null /*&& image.getImageStatus() != ImagesStatus.STATUS_IMAGE_ADDED.getStatus()*/){
                      DisplayMetrics displayMetrics = getResources().getDisplayMetrics();
                      float dpHeight = displayMetrics.heightPixels / displayMetrics.density;
                      float dpWidth = displayMetrics.widthPixels / displayMetrics.density;
                      float scale = getResources().getDisplayMetrics().density;
                      int marginHeightP = (int) (dpHeight * scale + 0.5f);
                      int marginWidthP = (int) (dpWidth * scale + 0.5f);
                      d = new BitmapDrawable(getResources(), Bitmap.createScaledBitmap(bitmap, marginWidthP, marginHeightP, true));
                  } else{
                      d = (getResources().getDrawable(R.drawable.pikard));
                  }
  
  
                  glide.load(filePath)
                          .placeholder(d)
                          .fitCenter()
                          .listener(new RequestListener<String, GlideDrawable>() {
  
                              @Override
                              public boolean onException(Exception e, String model, com.bumptech.glide.request.target.Target<GlideDrawable> target, boolean isFirstResource) {
                                  return false;
                              }
                              @Override
                              public boolean onResourceReady(GlideDrawable resource, String model, com.bumptech.glide.request.target.Target<GlideDrawable> target, boolean isFromMemoryCache, boolean isFirstResource) {
                                  pb.setVisibility(View.GONE);
                                  imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
                                  return false;
                              }
  
                          }).into(imageView);
  
              }
          }
          container.addView(relativeLayout, 0);
          return relativeLayout;
      }
  }
  

  And this is my XML file which i am using for using image inside the view pager

  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:androd="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  >
  
  <ImageView
      android:id="@+id/view_pager_image_view_show"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_centerVertical="true"
      android:layout_centerHorizontal="true"
      />
  
  </RelativeLayout>
  

  This is showing image like this inside the imageview when i set the scaleType centerInside

  but i want to show images inside the imageview like this

  
• Android LinearLayout created in Kotlin not rendering vertically

  I'm creating a custom keyboard layout in Kotlin (I have already written a very similar layout in Java that works well). For some reason I can't get this Kotlin version to render its LinearLayout vertically. Can anyone see if there are any obvious errors here? I've tried moving the orientation assignment to right before the calls to addView (in case it was getting re-assigned somewhere), but that's not working either. Here's the code for the class in question:

  abstract class KeyboardLayout(
      context: Context, private val controller: KeyboardController?) :
      LinearLayout(context) {
  
  private var screenWidth = 0.0f
  private var rowHeight = 0
  
  init {
      layoutParams = ViewGroup.LayoutParams(
              ViewGroup.LayoutParams.MATCH_PARENT,
              ViewGroup.LayoutParams.WRAP_CONTENT)
      orientation = LinearLayout.VERTICAL
  }
  
  fun createKeyboard(screenWidth: Float, rowHeight: Int) {
      this.screenWidth = screenWidth
      this.rowHeight = rowHeight
  
      for (row in createRows()) {
          addView(row)
      }
  }
  
  private fun createButton(text: String, widthAsPctOfScreen: Float): Button {
      val button = Button(context)
      button.layoutParams = LinearLayout.LayoutParams(
              (screenWidth * widthAsPctOfScreen).toInt(), rowHeight
      )
      button.textSize = 14.0f
      button.text = text
      return button
  }
  
  internal fun createButton(text: String, widthAsPctOfScreen: Float, c: Char): Button {
      val button = createButton(text, widthAsPctOfScreen)
      button.setOnClickListener { controller?.onKeyStroke(c) }
      return button
  }
  
  internal fun createButton(text: String, widthAsPctOfScreen: Float,
                            key: KeyboardController.SpecialKey): Button {
      val button = createButton(text, widthAsPctOfScreen)
      button.setOnClickListener { controller?.onKeyStroke(key) }
      return button
  }
  
  internal fun createSpacer(widthAsPctOfScreen: Float): View {
      val view = View(context)
      view.layoutParams = LinearLayout.LayoutParams(
              (screenWidth * widthAsPctOfScreen).toInt(), rowHeight
      )
      view.isEnabled = false
      view.visibility = View.INVISIBLE
      return view
  }
  
  internal fun createRow(buttons: List<View>): LinearLayout {
      val row = LinearLayout(context)
      row.layoutParams = LinearLayout.LayoutParams(
              ViewGroup.LayoutParams.MATCH_PARENT, rowHeight
      )
      orientation = LinearLayout.HORIZONTAL
      row.gravity = Gravity.CENTER
  
      for (button in buttons) {
          row.addView(button)
      }
      return row
  }
  
  internal abstract fun createRows(): List<LinearLayout>
  }
  
• Hyper-V is disabled. I cannot run intelhaxm-android.exe - ERROR: x86 emulation currently requires hardware acceleration

  I don't know why this error has occured. I have looked at other similar questions and have followed all protocol needed.

  I Know...

  1. My computer supports VT-X or Intel Virtualization Technology
  2. I have disabled Hyper-V in Windows Features
  3. I have enabled VT-X for Intel in BIOS for my Dell XPS-13

  I have tried everything but this does not work. Thanks in advance.

  The following errors occur after I try running my emulator (Nexus 5x API 28):

  Emulator: emulator: ERROR: x86 emulation currently requires hardware acceleration!
  
  Emulator: Process finished with exit code 1
  
• Upload Multiple image, PDF and DOC file from Webview

  I want to make a browser which will upload multiple image to web selecting from gallery. Like I want to choose multiple image with number and then upload it with a post button that Facebook has and it also can upload Pdf and Doc file to website.

  So what I did I searched a lot for this but at the end failed. I have tried this code which works for uploading single image from my webView to my website.

  import android.content.Context;
  import android.content.Intent;
  import android.net.Uri;
  import android.os.Bundle;
  import android.view.View;
  import android.webkit.JavascriptInterface;
  import android.webkit.ValueCallback;
  import android.webkit.WebChromeClient;
  import android.webkit.WebView;
  import android.webkit.WebViewClient;
  import java.io.*;
  import android.util.*;
  import java.text.*;
  import android.annotation.*;
  import java.util.*;
  import android.app.*;
  import android.provider.*;
  import android.os.*;
  import android.webkit.*;
  
  public class MainActivity extends Activity {
  
  public static final int REQUEST_CODE_LOLIPOP = 1;
  private final static int RESULT_CODE_ICE_CREAM = 2;
  private WebView webView;
  private ValueCallback<Uri[]> mFilePathCallback;
  private String mCameraPhotoPath;
  private ValueCallback<Uri> mUploadMessage;
  
  private String url ="http://up.example.com";
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
  
  
      webView = (WebView) findViewById(R.id.wbvw);
      setUpWebViewDefaults(webView);
      webView.loadUrl(url);
  
  
  
      webView.setWebChromeClient(new WebChromeClient() {
              private String TAG;
              // For Android 3.0+
              public void openFileChooser(ValueCallback<Uri> uploadMsg) {
                  mUploadMessage = uploadMsg;
                  Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                  i.addCategory(Intent.CATEGORY_OPENABLE);
                  i.setType("image/*");
                  startActivityForResult(Intent.createChooser(i, "File Chooser"),
                                         RESULT_CODE_ICE_CREAM);
  
              }
              // For Android 3.0+
              public void openFileChooser(ValueCallback uploadMsg, String acceptType) {
                  mUploadMessage = uploadMsg;
                  Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                  i.addCategory(Intent.CATEGORY_OPENABLE);
                  i.setType("*/*");
                  startActivityForResult(Intent.createChooser(i, "File Browser"),
                                         RESULT_CODE_ICE_CREAM);
              }
              //For Android 4.1
              public void openFileChooser(ValueCallback<Uri> uploadMsg, String acceptType, String capture) {
                  mUploadMessage = uploadMsg;
                  Intent i = new Intent(Intent.ACTION_GET_CONTENT);
                  i.addCategory(Intent.CATEGORY_OPENABLE);
                  i.setType("image/*");
                  startActivityForResult(Intent.createChooser(i, "File Chooser"),
                                         RESULT_CODE_ICE_CREAM);
  
              }
              //For Android5.0+
              public boolean onShowFileChooser(
                  WebView webView, ValueCallback<Uri[]> filePathCallback,
                  FileChooserParams fileChooserParams) {
                  if (mFilePathCallback != null) {
                      mFilePathCallback.onReceiveValue(null);
                  }
                  mFilePathCallback = filePathCallback;
                  Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                  if (takePictureIntent.resolveActivity(MainActivity.this.getPackageManager()) != null) {
                      // Create the File where the photo should go
                      File photoFile = null;
                      try {
                          photoFile = createImageFile();
                          takePictureIntent.putExtra("PhotoPath", mCameraPhotoPath);
                      } catch (IOException ex) {
                          // Error occurred while creating the File
                          Log.e(TAG, "Unable to create Image File", ex);
                      }
                      // Continue only if the File was successfully created
                      if (photoFile != null) {
                          mCameraPhotoPath = "file:" + photoFile.getAbsolutePath();
                          takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT,
                                                     Uri.fromFile(photoFile));
                      } else {
                          takePictureIntent = null;
                      }
                  }
                  Intent contentSelectionIntent = new Intent(Intent.ACTION_GET_CONTENT);
                  contentSelectionIntent.addCategory(Intent.CATEGORY_OPENABLE);
                  contentSelectionIntent.setType("image/*");
                  Intent[] intentArray;
                  if (takePictureIntent != null) {
                      intentArray = new Intent[]{takePictureIntent};
                  } else {
                      intentArray = new Intent[0];
                  }
                  Intent chooserIntent = new Intent(Intent.ACTION_CHOOSER);
                  chooserIntent.putExtra(Intent.EXTRA_INTENT, contentSelectionIntent);
                  chooserIntent.putExtra(Intent.EXTRA_TITLE, "Image Chooser");
                  chooserIntent.putExtra(Intent.EXTRA_INITIAL_INTENTS, intentArray);
  
                  startActivityForResult(chooserIntent, REQUEST_CODE_LOLIPOP);
  
                  return true;
              }
          });
  }
  private File createImageFile() throws IOException {
      // Create an image file name
      String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
      String imageFileName = "JPEG_" + timeStamp + "_";
      File storageDir = Environment.getExternalStoragePublicDirectory(
          Environment.DIRECTORY_PICTURES);
      File imageFile = File.createTempFile(
          imageFileName,  /* prefix */
          ".jpg",         /* suffix */
          storageDir      /* directory */
      );
      return imageFile;
  }
  @TargetApi(Build.VERSION_CODES.HONEYCOMB)
  private void setUpWebViewDefaults(WebView webView) {
      WebSettings settings = webView.getSettings();
      // Enable Javascript
      settings.setJavaScriptEnabled(true);
      // Use WideViewport and Zoom out if there is no viewport defined
      settings.setUseWideViewPort(true);
      settings.setLoadWithOverviewMode(true);
      // Enable pinch to zoom without the zoom buttons
      settings.setBuiltInZoomControls(true);
      if (Build.VERSION.SDK_INT > Build.VERSION_CODES.HONEYCOMB) {
          // Hide the zoom controls for HONEYCOMB+
          settings.setDisplayZoomControls(false);
      }
      // Enable remote debugging via chrome://inspect
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
          WebView.setWebContentsDebuggingEnabled(true);
      }
      // We set the WebViewClient to ensure links are consumed by the WebView rather
      // than passed to a browser if it can
      webView.setWebViewClient(new WebViewClient());
  }
  @Override
  public void onActivityResult(int requestCode, int resultCode, Intent data) {
      super.onActivityResult(requestCode, resultCode, data);
      switch (requestCode) {
          case RESULT_CODE_ICE_CREAM:
              Uri uri = null;
              if (data != null) {
                  uri = data.getData();
              }
              mUploadMessage.onReceiveValue(uri);
              mUploadMessage = null;
              break;
          case REQUEST_CODE_LOLIPOP:
              Uri[] results = null;
              // Check that the response is a good one
              if (resultCode == Activity.RESULT_OK) {
                  if (data == null) {
                      // If there is not data, then we may have taken a photo
                      if (mCameraPhotoPath != null) {
                          results = new Uri[]{Uri.parse(mCameraPhotoPath)};
                      }
                  } else {
                      String dataString = data.getDataString();
                      if (dataString != null) {
                          results = new Uri[]{Uri.parse(dataString)};
                      }
                  }
              }
              mFilePathCallback.onReceiveValue(results);
              mFilePathCallback = null;
              break;
        }
       }
     }
  
• Android Fileread dont read my file but it works on IntelliJ

  I need some help with my Anagramm-create app for android in Android-Studio. I intended to get the words from a text file, probably .txt . My problem at the moment is, that the app use the catch block of my Scanner instead of reading the file. If I open it with IntelliJ it works without a problem.

  It would be very nice, if somebody can give me a advice to solve the first word problem(class 2).(low priority)

  Class 1:

  public class library {
  
  private static String[] words = {"Aaaa"};
  
  library() {
      try (Scanner s = new Scanner(new File(System.getProperty("user.dir") + ("/words.txt")))) {
          s.useDelimiter("\\,");
          String[] array = {"AALBESTAND"};
          while (s.hasNext()) {
              array = Arrays.copyOf(array, array.length + 1); //create new array from old array and allocate one more element
              array[array.length - 1] = s.next();
              words = array;
          }
      } catch (FileNotFoundException e) {
          words = Arrays.copyOf(words,words.length+1);
          words[words.length-1]="Bbbb";
      }
  }
  

  Class 2:

  public class words extends AppCompatActivity {
  
  
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_words);
      final library library = new library();
      library.getWord();
  
      /**
       * Declaration
       */
  
      final Button button_check = (Button) findViewById(R.id.button_check);
      final Button button_next = (Button) findViewById(R.id.button_next);
      final TextView textView = (TextView) findViewById(R.id.textView);
      final RadioButton radioButton1 = (RadioButton) findViewById(R.id.radioButton1);
      final RadioButton radioButton2 = (RadioButton) findViewById(R.id.radioButton2);
      final RadioButton radioButton3 = (RadioButton) findViewById(R.id.radioButton3);
      final RadioButton radioButton4 = (RadioButton) findViewById(R.id.radioButton4);
      final RadioButton radioButton5 = (RadioButton) findViewById(R.id.radioButton5);
      String[] alphabet = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "K", "L", "M", "N", "O", "P", "R", "S", "T", "U"}; // necessary for the first word dont know why
      textView.setText(library.randomize());
  
  
      radioButton1.setText(String.valueOf(alphabet[(int) (Math.random() * 19)]));    // necessary for the first word
      radioButton2.setText(String.valueOf(alphabet[(int) (Math.random() * 19)]));    // necessary for the first word
      radioButton3.setText(String.valueOf(alphabet[(int) (Math.random() * 19)]));    // necessary for the first word
      radioButton4.setText(String.valueOf(alphabet[(int) (Math.random() * 19)]));    // necessary for the first word
  
  
      /**
       *  new word and reset the buttons and text colour
       *  without using check
       */
  
      button_next.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View view) {
              radioButton1.setChecked(false);                 //reset buttons
              radioButton2.setChecked(false);                 //reset buttons
              radioButton3.setChecked(false);                 //reset buttons
              radioButton4.setChecked(false);                 //reset buttons
              radioButton5.setChecked(false);                 //reset buttons
  
              radioButton1.setTextColor(Color.BLACK);         //textColour = black
              radioButton2.setTextColor(Color.BLACK);         //textColour = black
              radioButton3.setTextColor(Color.BLACK);         //textColour = black
              radioButton4.setTextColor(Color.BLACK);         //textColour = black
              radioButton5.setTextColor(Color.BLACK);         //textColour = black
  
              textView.clearComposingText();                  //delete old word
              String random = library.randomize();            //create new word
              textView.setText(library.getWord());            //insert new word
              textView.setText(random);                       //dont know why i needed this one, but i am sure i needed it
  
              /**
               * check if the text of multiple choice answers are the same
               * had problems without try catch
               */
              try {
                  String rb1 = createValue(random), rb2 = createValue(random), rb3 = createValue(random), rb4 = createValue(random);
                  while (rb2.equals(rb1)) rb2 = createValue(random);
                  while ((rb3.equals(rb1)) ^ (rb3.equals(rb2))) rb3 = createValue(random);
                  while ((rb4.equals(rb1)) ^ (rb4.equals(rb2)) ^ (rb4.equals(rb3)))
                      rb4 = createValue(random);
                  radioButton1.setText(rb1);
                  radioButton2.setText(rb2);
                  radioButton3.setText(rb3);
                  radioButton4.setText(rb4);
              } catch (Exception e) {
                  button_next.performClick();
              }
          }
      });
     }
  /**
   * @param word is the searched word
   * @return a letter of the word task
   */
  private String createValue(String word) {
      return String.valueOf(word.charAt((int) (word.length() * Math.random())));
  }
  }
  
• USB Communication between android and PC

  Background :I have tried finding help on stackoverflow, android developers, and various other resources on web. This is my last hope. I am new to communication and starting with implementation of USB. Following are my questions:

  1) When I connect my phone to windows PC, which one is host? Suppose I want to create an application that can send data, am I making my phone host?

  2) For the case (Windows PC and Android phone), the other one would be a peripheral or a device? are they same?

  3) From android developers website and a windows forum about USB, I understand that there are certain steps that need to be followed, and it's like - Create an instance of USBManager. - Create get list of devices - Choose a device from which you want to establish connection - Create an interface - get endpoint from that interface. - Create instance of DeviceConnections and call bulkTransfer method and send data.

  But when I tried above steps, I get device == null. I don't even know if my understanding for above communication method is correct.

  Can someone please help me understand and establish basic communication between a PC and a android phone and send at least "hello world".

  Big thank you for even reading such a long question.

  Here is code sample of what I have done. here devicelist returns null.

   public class MainActivity extends AppCompatActivity {
  
      android.widget.Button usbButton;
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          final CustomUSBManager cmanager = new CustomUSBManager();
  
  //1)        //Create instance of USB Manager using getSystemService
          final UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
  
  //2)        //Create a list of devices
          HashMap<String,UsbDevice> deviceList = manager.getDeviceList();
  
          Log.d("Devicelist = ", String.valueOf(deviceList.get(0)));
  
  //3)        //Get a specific device from the list
  
  
  
  //-----------------------------------------------------------------
  
  Here is my manifest file.
  
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.example.neeraj.usbcommunication1">
      <uses-feature android:name="android.hardware.usb.host"></uses-feature>
  
      <application
          android:allowBackup="true"
          android:icon="@mipmap/ic_launcher"
          android:label="@string/app_name"
          android:roundIcon="@mipmap/ic_launcher_round"
          android:supportsRtl="true"
          android:theme="@style/AppTheme">
          <activity android:name=".MainActivity">
              <intent-filter>
                  <action android:name="android.intent.action.MAIN" />
  
                  <category android:name="android.intent.category.LAUNCHER" />
              </intent-filter>
  
          </activity>
      </application>
  
  </manifest> 
          final UsbDevice device = deviceList.get(0); //getting first device
  
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