Android finger drawing (2)

package cn.c;import android.app.Activity;import android.graphics.Bitmap;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.os.Bundle;import android.view.Display;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;import android.widget.ImageView;public class MainActivity extends Activity{    private ImageView mImageView;    private Bitmap mBitmap;    private Paint mPaint;    private Canvas mCanvas;    float downX=0;    float downY=0;    float upX=0;    float upY=0;        @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        mImageView=(ImageView) findViewById(R.id.imageView);        Display display=getWindowManager().getDefaultDisplay();        int w=display.getWidth();        int h=display.getHeight();        mBitmap=Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);        mCanvas=new Canvas(mBitmap);        mPaint=new Paint();        mPaint.setColor(Color.RED);        mImageView.setImageBitmap(mBitmap);    }    @Overridepublic boolean onTouchEvent(MotionEvent event) {int action = event.getAction();switch (action) {case MotionEvent.ACTION_DOWN:            downX=event.getX();            downY=event.getY();break;case MotionEvent.ACTION_MOVE:upX=event.getX();            upY=event.getY();            mCanvas.drawLine(downX, downY, upX, upY, mPaint);            mImageView.invalidate();            downX=upX;            downY=upY;break;case MotionEvent.ACTION_UP:            upX=event.getX();            upY=event.getY();            mCanvas.drawLine(downX, downY, upX, upY, mPaint);            mImageView.invalidate();break;case MotionEvent.ACTION_CANCEL:break;default:break;}return true;}   }