Get the canvas bitmap of custom View

I have a series of previous articles to draw something on custom view's canvas. All these code lose everythng after the app exit. Now I want to save the drawing in a file. In this article, I will demonstrate how to get the canvas bitmap of custom view. In next article, I will show how to save in file.

When user want to capture the canvas bitmap, touch MENU -> Capture Canvas.

I don't know why I can't get the bitmap of the custom view by getDrawingCache() as shown in the article "Capture Screen, using View.getDrawingCache()"! So I create a separated bitmap and canvas to draw on (I also used this method to solve "Flickering problems due to double buffer of SurfaceView" in former article).

- In onMeasure() of my custom view(MyView), create a bitmap(myCanvasBitmap) and canvas(myCanvas). And apply myCanvasBitmap on myCanvas.

- When I have to draw something in onDraw(), I draw on myCanvas. It will draw on myCanvasBitmap. Then apply myCanvasBitmap to the view's canvas. Also, I have to erase myCanvasBitmap on TouchEvent of MotionEvent.ACTION_DOWN.

- When I need the bitmap, when getCanvasBitmap() is called, simple return myCanvasBitmap.

The code of my custom view, MyView.java.

package com.AndroidMyCanvas;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class MyView extends View {
 
 boolean freeTouched = false;
 Path freePath;
 
 Bitmap myCanvasBitmap = null;
 Canvas myCanvas = null;
 
 Matrix identityMatrix;

 public MyView(Context context) {
  super(context);
 }

 public MyView(Context context, AttributeSet attrs) {
  super(context, attrs);
 }

 public MyView(Context context, AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
 }
 
 @Override
 protected void onDraw(Canvas canvas) {
    
  if(freeTouched){
   Paint paint = new Paint();
   paint.setStyle(Paint.Style.STROKE);
   paint.setColor(Color.RED);
   paint.setStrokeWidth(10);
   
   myCanvas.drawPath(freePath, paint);
   canvas.drawBitmap(myCanvasBitmap, identityMatrix, null);
   
  }
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
  
  switch(event.getAction()){
  case MotionEvent.ACTION_UP:
   freeTouched = false;
   break;
  case MotionEvent.ACTION_DOWN:
   freeTouched = true;
   freePath = new Path();
   freePath.moveTo(event.getX(), event.getY());
   
   myCanvasBitmap.eraseColor(Color.BLACK);
   
   break;
  case MotionEvent.ACTION_MOVE:
   freePath.lineTo(event.getX(), event.getY());
   invalidate();
   break;
  }
  
  return true;
 }
 
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

  int w = MeasureSpec.getSize(widthMeasureSpec);
  int h = MeasureSpec.getSize(heightMeasureSpec);

  myCanvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
  myCanvas = new Canvas();
  myCanvas.setBitmap(myCanvasBitmap);
  
  identityMatrix = new Matrix();
  
  setMeasuredDimension(w, h);
 }

 public Bitmap getCanvasBitmap(){
  
  return myCanvasBitmap;
  
 }

}

Create /res/menu/menu.xml to define our option menu.

<?xml version="1.0" encoding="UTF-8"?>
    <menu xmlns:android="http://schemas.android.com/apk/res/android">
        <item 
            android:id="@+id/opt_capture"
            android:title="Capture Canvas" />
    </menu>

The main code, AndroidMyCanvasActivity.java.

package com.AndroidMyCanvas;

import android.app.Activity;
import android.app.AlertDialog;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.ViewGroup.LayoutParams;
import android.widget.ImageView;
import android.widget.LinearLayout;

public class AndroidMyCanvasActivity extends Activity {
 
 MyView myView;
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        myView = new MyView(this);

        setContentView(myView);
        
    }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  MenuInflater menuInflater = getMenuInflater();
  menuInflater.inflate(R.menu.menu, menu);
  return true;
 }

 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
  switch(item.getItemId()){
  case R.id.opt_capture:
   openCaptureDialog();
   return true;
  default:
   return false;
  
  }
 }
 
 private void openCaptureDialog(){

  Bitmap bmMyView = myView.getCanvasBitmap();

  AlertDialog.Builder captureDialog = new AlertDialog.Builder(AndroidMyCanvasActivity.this);
  captureDialog.setTitle("Canvas Captured");
  
  ImageView bmImage = new ImageView(AndroidMyCanvasActivity.this);
  
     bmImage.setImageBitmap(bmMyView);
     
     LayoutParams bmImageLayoutParams = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);
     bmImage.setLayoutParams(bmImageLayoutParams);
      
     LinearLayout dialogLayout = new LinearLayout(AndroidMyCanvasActivity.this);
     dialogLayout.setOrientation(LinearLayout.VERTICAL);
     dialogLayout.addView(bmImage);
     captureDialog.setView(dialogLayout);
     
  captureDialog.setPositiveButton("OK", null);
  captureDialog.show();
     
 }

}