android学习笔记六

 1 import android.media.MediaPlayer;
 2 import android.os.Bundle;
 3 import android.app.Activity;
 4 import android.graphics.Bitmap;
 5 import android.graphics.BitmapFactory;
 6 import android.graphics.Canvas;
 7 import android.graphics.Color;
 8 import android.graphics.Matrix;
 9 import android.graphics.Paint;
10 import android.view.Menu;
11 import android.view.MotionEvent;
12 import android.view.View;
13 import android.view.View.OnTouchListener;
14 import android.widget.ImageView;
15 
16 public class MainActivity extends Activity {
17     private ImageView iv;
18     // 可以修改的位图
19     private Bitmap alertBitmap;
20     private Canvas canvas;
21 
22     @Override
23     protected void onCreate(Bundle savedInstanceState) {
24         super.onCreate(savedInstanceState);
25         setContentView(R.layout.activity_main);
26         iv = (ImageView) findViewById(R.id.iv);
27         Bitmap bitmap = BitmapFactory.decodeResource(getResources(),
28                 R.drawable.pre);
29 
30         // 创建一个空白的原图的拷贝
31         alertBitmap = Bitmap.createBitmap(bitmap.getWidth(),
32                 bitmap.getHeight(), bitmap.getConfig());
33         //使用画图API为空白图进行绘制
34         canvas = new Canvas(alertBitmap);
35         Paint paint = new Paint();
36         paint.setColor(Color.BLACK);
37         canvas.drawBitmap(bitmap, new Matrix(), paint);
38         iv.setImageBitmap(alertBitmap);
39 
40         iv.setOnTouchListener(new OnTouchListener() {
41             @Override
42             public boolean onTouch(View v, MotionEvent event) {
43                 switch (event.getAction()) {
44                 case MotionEvent.ACTION_DOWN:// 手指按下屏幕
45                     System.out.println("action down");
46                     break;
47                 case MotionEvent.ACTION_MOVE:// 手指在屏幕上移动
48                     int x = (int) event.getX();
49                     int y = (int) event.getY();
50                     System.out.println("设置("+x+","+y+")透明颜色");
51                     //1、下面是将触摸点一定范围的点全部变透明,这样效果明显
52                     for(int i=-4;i<5;i++){
53                         for(int j=-4;j<5;j++){
54                             //2、这里的异常是处理范围超过控件的范围而报的异常,
55                             try{
56                                 alertBitmap.setPixel(x+i, y+j, Color.TRANSPARENT);
57                             }catch (Exception e) {
58                             }
59                         }
60                     }
61                     iv.setImageBitmap(alertBitmap);
62                     break;
63                 case MotionEvent.ACTION_UP:// 手指离开屏幕
64                     MediaPlayer.create(getApplicationContext(), R.raw.higirl).start();
65                     break;
66                 }
67                 return true;//3、返回true指可以重复循环的处理事件,否则只能处理一个事件(按下/移动/离开)
68             }
69         });
70     }
71 
72 }