android activity中画任意直线

这里的画直线不是通过新建一个View类，在View的画布中画，而是直接在activity中画。

package lizm.lt;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.Menu;
import android.widget.LinearLayout;
import android.widget.TextView;

public class MainActivity extends Activity {
	private LinearLayout mylayout;
	private TextView tt;
	private Bitmap bitmap;
	private int x=0, y=0, xx=800, yy=480;
	Paint paint;
	Canvas canvas;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mylayout = (LinearLayout)findViewById(R.id.myLayout);
        tt = (TextView)findViewById(R.id.myText);
        
        paint = new Paint();  

		paint.setStrokeWidth(5);//笔宽5像素
		paint.setColor(Color.RED);//设置为红笔
	//	paint.setAntiAlias(false);//锯齿不显示
		
		bitmap = Bitmap.createBitmap(800, 480, Bitmap.Config.ARGB_8888); //设置位图的宽高,bitmap为透明
		canvas = new Canvas(bitmap);
		canvas.drawColor(Color.TRANSPARENT,PorterDuff.Mode.CLEAR);//设置为透明，画布也是透明
		
		
		canvas.drawLine(0, 20, 750, 200, paint);
		
		//在画布上贴张小图
		Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);   
		canvas.drawBitmap(bm, 0, 0, paint);
		
		
		
		
		paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));//橡皮擦一样擦除 
		canvas.drawLine(0, 20, 750, 200, paint);
		
		paint.setXfermode(null);//取消擦除模式
		paint.setColor(Color.BLUE);
		canvas.drawLine(0, 20, 750, 200, paint);
		
		
		Drawable drawable = new BitmapDrawable(bitmap) ;  
		mylayout.setBackgroundDrawable(drawable);
		


		
	}

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
    
    
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
    	// TODO Auto-generated method stub
    	
    	if(keyCode == 19){
    		
    		paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));//橡皮擦一样擦除 
    		canvas.drawLine(x, y, xx, yy, paint);
    		
    		
    		x +=20;
    		y +=20;
    		xx-=20;
    		yy-=20;
    		paint.setXfermode(null);//取消擦除模式
    		paint.setColor(Color.BLUE);
    		canvas.drawLine(x, y, xx, yy, paint);
    		
    		
    		Drawable drawable = new BitmapDrawable(bitmap) ;  
    		mylayout.setBackgroundDrawable(drawable);
    	}
    	
    	return super.onKeyDown(keyCode, event);
    }
}

 

 

运行效果，如下，每按一次方向上键，就擦除上一条直线，重画另一条直线