ImageView.setOnClickListener ERROR空对象引用

Question

我加入setonclick监听方法后得到一个错误：

CODE：

ImageView first, second_img; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     first = (ImageView) findViewById(R.id.first_image); 
     second_img = (ImageView)findViewById(R.id.second_image); 

     setContentView(R.layout.main); 

     first.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       Intent get_img = new Intent(); 
       get_img.setType("image/*"); 
       get_img.setAction(Intent.ACTION_GET_CONTENT); 
       startActivityForResult(Intent.createChooser(get_img, "Select Picture"), 1); 
      } 
     }); 

     Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.anonymous); 
     ByteArrayOutputStream stream = new ByteArrayOutputStream(); 
     bmp.compress(Bitmap.CompressFormat.PNG, 100, stream); 
     byte[] bytes = stream.toByteArray(); 

     //for(byte bite: bytes){ 
     // System.out.println("@@@: " + bite); 
     //} 

     Bitmap second_bmp = BitmapFactory.decodeByteArray(bytes, 0, bytes.length); 
     second_img.setImageBitmap(second_bmp); 
    } 

错误：

Process: com.example.example, PID: 3100 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.example/com.example.example.example}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 

我不知道是什么继续，有人帮助我，我会感谢您的帮助，谢谢。

Answer 1

正确的顺序应该是：

 setContentView(R.layout.main); 
    first = (ImageView) findViewById(R.id.first_image); 
    second_img = (ImageView)findViewById(R.id.second_image); 

否则，第一和second_img将为空。