Android：将imageview转换为位图，灰度，将位图转换为imageview

Question

当我编译此代码时，我不会在eclipse上得到任何警告，但是当我在设备或模拟器上运行它时，该程序被迫关闭。

public class MainActivity extends Activity { 

    ImageView img; 
    Button btn; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     //convert imageview to bitmap 
     img =(ImageView) findViewById(R.id.imageView1); 
     BitmapDrawable drawable = (BitmapDrawable) img.getDrawable(); 
     final Bitmap imgbitmap = drawable.getBitmap(); 


     btn.setOnClickListener(new View.OnClickListener() { 
      public void onClick(View v) { 
       //convert bitmap to grayscale 
       Bitmap imgnew; 
       imgnew = toGrayscale(imgbitmap);  

       //convert bitmap to imageview 
       ImageView imgbit; 
       imgbit = (ImageView) findViewById(R.id.imageView2); 
       imgbit.setImageBitmap(imgnew); 
      } 
     }); 

    } 

    public Bitmap toGrayscale(Bitmap bmpOriginal){   
     int width, height; 
     height = bmpOriginal.getHeight(); 
     width = bmpOriginal.getWidth();  

     Bitmap bmpGrayscale = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565); 
     Canvas c = new Canvas(bmpGrayscale); 
     Paint paint = new Paint(); 
     ColorMatrix cm = new ColorMatrix(); 
     cm.setSaturation(0); 
     ColorMatrixColorFilter f = new ColorMatrixColorFilter(cm); 
     paint.setColorFilter(f); 
     c.drawBitmap(bmpOriginal, 0, 0, paint); 
     return bmpGrayscale; 
    } 

} 

Answer 1

如果上面是你的全代码，然后，根本的问题是有，你有没有定义btn。你需要在使用它之前定义它，否则当你自己点击按钮时它将不起作用。这可能会关闭你的应用程序。

btn=(Button) findViewById(R.id.button1);