How to convert a LinearLayout to image?

Bitmap b = Bitmap.createBitmap(lyt.getDrawingCache());

the only thing that can be null in that line is lyt, the rest can't. You probably did not set the layout yet and findViewById() will return null in that case.

You have to do setContentView() before you can do findViewById()

Try below code, it work

Add below permission in manifest

     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

MainActivity.java

    public class MainActivity extends Activity implements OnClickListener{
    private LinearLayout linearLayout;
    private Button saveBtn;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        linearLayout = (LinearLayout) findViewById(R.id.linearLayout_view);
        saveBtn = (Button) findViewById(R.id.save_btn);
        saveBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        int id = v.getId();
        switch (id) {
        case R.id.save_btn:
            File file = saveBitMap(this, linearLayout);    //which view you want to pass that view as parameter
            if (file != null) {
                Log.i("TAG", "Drawing saved to the gallery!");
            } else {
                Log.i("TAG", "Oops! Image could not be saved.");
            }
            break;
        default:
            break;
        }

    private File saveBitMap(Context context, View drawView){
        File pictureFileDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES),"Handcare");
        if (!pictureFileDir.exists()) {
            boolean isDirectoryCreated = pictureFileDir.mkdirs();
            if(!isDirectoryCreated)
                Log.i("ATG", "Can't create directory to save the image");
            return null;
        }
        String filename = pictureFileDir.getPath() +File.separator+ System.currentTimeMillis()+".jpg";
        File pictureFile = new File(filename);
        Bitmap bitmap =getBitmapFromView(drawView);
        try {
            pictureFile.createNewFile();
            FileOutputStream oStream = new FileOutputStream(pictureFile);
            bitmap.compress(CompressFormat.PNG, 100, oStream);
            oStream.flush();
            oStream.close();
        } catch (IOException e) {
            e.printStackTrace();
            Log.i("TAG", "There was an issue saving the image.");
        }       
            scanGallery( context,pictureFile.getAbsolutePath());
        return pictureFile;
    }
    //create bitmap from view and returns it
    private Bitmap getBitmapFromView(View view) {
        //Define a bitmap with the same size as the view
        Bitmap returnedBitmap = Bitmap.createBitmap(view.getWidth(), view.getHeight(),Bitmap.Config.ARGB_8888);
        //Bind a canvas to it
        Canvas canvas = new Canvas(returnedBitmap);
        //Get the view's background
        Drawable bgDrawable =view.getBackground();
        if (bgDrawable!=null) {
            //has background drawable, then draw it on the canvas
            bgDrawable.draw(canvas);
        }   else{
            //does not have background drawable, then draw white background on the canvas
            canvas.drawColor(Color.WHITE);
        }
        // draw the view on the canvas
        view.draw(canvas);
        //return the bitmap
        return returnedBitmap;
    }
    // used for scanning gallery
    private void scanGallery(Context cntx, String path) {
        try {
            MediaScannerConnection.scanFile(cntx, new String[] { path },null, new MediaScannerConnection.OnScanCompletedListener() {
                public void onScanCompleted(String path, Uri uri) {
                }
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

My guess is that you are executing that code in onCreate. The problem with that is that the views are not layouted yet. Either call lyt.measure or call the code later. e.g: to onSizeChanged() or in onLayout() after you called super.onLayout().