NullpointerException when trying to save the current Android app view as image

Hi stackoverflow community,

in my application I'd like to have a button which allows the user to capture the current view. For that reason, I've written the following method (oriented towards: Android save view to jpg or png ):

private LinearLayout container; 
 
 public void createImageOfCurrentView(View v) {
             if(isExternalStoragePresent()) {
                 container = findViewById(R.id.container);
                 container.setDrawingCacheEnabled(true);
                 Bitmap b = container.getDrawingCache(); 
                 File dir = new File(Environment.getExternalStorageDirectory().getPath()+"/"+getPackageName()+"/");
                 dir.mkdirs();
                 File file = new File(dir, "image.jpg");
                 FileOutputStream fos;
                 try {
                     fos = new FileOutputStream(file);              
                     b.compress(CompressFormat.JPEG, 95, fos); // NullPointerException!                  
                     Toast.makeText(this, "The current view has been succesfully saved as image.", Toast.LENGTH_SHORT).show();
                 } catch (FileNotFoundException e) {
                     Toast.makeText(this, "Unfortunatly an error occured and this action failed.", Toast.LENGTH_SHORT).show();
             }   
             }else {
                 Toast.makeText(this, "Bacause of lacking access to the storage of this device, the current view couldn't be saved as an image.", Toast.LENGTH_LONG).show();
             }
         }           
 

The problem is according to LogCat that there occured a NullPointerException when trying to create the jpeg. So probably the method container.getDrawingCache() is not working. On the phone the file is generated. However with the size of 0 bytes and no visible image. I would appreciate any suggestions what I have to do in order to make it work as I want.

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