'this'關鍵字不起作用

Question

我使用for循環創建了一些ImageView s，並將它們插入到ScrollView中。

然後我需要在觸摸屏幕時再創建一個ImageView。 this關鍵字不能用於在'###'標記的位置創建ImageView。

我是初學者。

public class MainActivity extends ActionBarActivity { 

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

     final ScrollView scroll=new ScrollView(this); 

     final LinearLayout layout =new LinearLayout(this); 
     layout.setOrientation(LinearLayout.VERTICAL); 
     layout.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT, LinearLayout.LayoutParams.FILL_PARENT)); 

     final LinearLayout.LayoutParams lparams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT); 
     lparams.setMargins(0, 10, 0, 10); 
     lparams.gravity=Gravity.CENTER; 

     int i; 

     for(i=0;i<15;i++) { 
      //here 'this' is working ****************** 
      ImageView imView = new ImageView(this); 
      imView.setLayoutParams(lparams); 

      Drawable new_image = getResources().getDrawable(R.drawable.rakthasakshi); 
      imView.setBackgroundDrawable(new_image); 

      layout.addView(imView, lparams); 

     } 
     scroll.addView(layout); 
     setContentView(scroll); 

     scroll.setOnTouchListener(new View.OnTouchListener() { 
      @Override 
      public boolean onTouch(View v, MotionEvent event) { 

       if(event.getAction() == MotionEvent.ACTION_UP){ 

        //but here says 'this' cannot be applied ############### 
        ImageView imView = new ImageView(this); 
        imView.setLayoutParams(lparams); 

        Drawable new_image = getResources().getDrawable(R.drawable.rakthasakshi); 
        imView.setBackgroundDrawable(new_image); 

        layout.addView(imView, lparams); 

        scroll.addView(layout); 
        setContentView(scroll); 

        return true; 
       } 
       return false; 
      } 
     }); 


    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 

     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 
    } 
} 

Answer 1

使用ImageView imView = new ImageView(MainActivity.this);。

在第一種情況下，this已經指MainActivity。

但是，在第二種情況下，this實際上是指View.OnTouchListener。

Answer 2

添加具有此功能並使用它的最終上下文。

例子：

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

     final ScrollView scroll=new ScrollView(this); 
     final Context ctx = this; 

... 


     //but here says 'this' cannot be applied ############### 
     ImageView imView = new ImageView(ctx); 

Answer 3

你知道什麼this意味着你的背景？

this引用View.OnTouchListener類型的匿名類。

要引用您的類MainActivity的對象，您必須引用MainActivity.this。

Answer 4

此關鍵字在父類中運行良好，但是在創建子類時，必須使用ActivityName.this而不是this。