学步园

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);
    }
    
	@Override
	public 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;
	}
   
}