ImageView.setOnClickListener 错误空对象引用

Question

添加 setonclick 侦听器方法后出现错误：

代码：

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

我不知道怎么回事，有人帮我，我很感激你的帮助，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，first 和 second_img 将为空。

ImageView.setOnClickListener 错误空对象引用

ImageView.setOnClickListener ERROR null object reference

android

image

imageview

onclicklistener