不能在类中使用xml来扩展视图

Question

这里是错误，似乎指向在DrawView中定义的init（）函数中的空指针。 我想显示一些在onDraw（）上绘制的形状，在它下面显示一个按钮。

致命异常：主要 android.view.InflateException：二进制XML文件行＃7：错误充气类

com.example.canvas_shapes2.DrawView 
at android.view.LayoutInflater.createView(LayoutInflater.java:606) 
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:680) 
at android.view.LayoutInflater.rInflate(LayoutInflater.java:739) 
at android.view.LayoutInflater.inflate(LayoutInflater.java:489) 
at android.view.LayoutInflater.inflate(LayoutInflater.java:396) 
at android.view.LayoutInflater.inflate(LayoutInflater.java:352) 
at 
com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:269) 
at android.app.Activity.setContentView(Activity.java:1885) 
at com.example.canvas_shapes2.MainGameScreen$1.onClick(MainGameScreen.java:31) 
at android.view.View.performClick(View.java:3549) 
at android.view.View$PerformClick.run(View.java:14400) 
at android.os.Handler.handleCallback(Handler.java:605) 
at android.os.Handler.dispatchMessage(Handler.java:92) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:4944) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
at dalvik.system.NativeStart.main(Native Method) 

Caused by: java.lang.reflect.InvocationTargetException 
at java.lang.reflect.Constructor.constructNative(Native Method) 
at java.lang.reflect.Constructor.newInstance(Constructor.java:417) 
at android.view.LayoutInflater.createView(LayoutInflater.java:586) 
... 19 more 

Caused by: java.lang.NullPointerException 
at com.example.canvas_shapes2.DrawView.init(DrawView.java:271) 
at com.example.canvas_shapes2.DrawView.<init>(DrawView.java:254) 

game_screen.xml 

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="fill_parent" 
android:layout_height="fill_parent" 
android:orientation="vertical" > 

<view class="com.example.canvas_shapes2.DrawView" 
    android:id="@+id/dview" 
    android:layout_width="wrap_content" 
    android:layout_height="370dp" 

/> 


<LinearLayout 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:orientation="horizontal" 
    > 

    <Button 
     android:id="@+id/display_challengeX" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="@string/display_challenge_button" 

     /> 

</LinearLayout> 

</LinearLayout> 

public class MainGameScreen extends FragmentActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    setContentView(R.layout.activity_main); 

    findViewById(R.id.start_game0).setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View v) { 

      DialogFragment newFragment = new DialogBox(); 

      newFragment.show(getSupportFragmentManager(), "chall_diag"); 
      setContentView(R.layout.game_screen); 

     } 
    }); 

public class DrawView extends View { 


public DrawView(Context context) { 
    super(context); 

} 

public DrawView(Context context, AttributeSet attrs) { 
    super(context, attrs); 

    init(context); 
} 


private void init(Context ctx) { 

    Button button = (Button) findViewById(R.id.display_challengeX); 
    button.setOnClickListener(new View.OnClickListener() { 
     public void onClick(View v) { 
      System.out.println("ABC"); 
     } 
    }); 

} 

Answer 1

想通了，只好搬到：

Button button = (Button) findViewById(R.id.display_challengeX); 
button.setOnClickListener(new View.OnClickListener() { 
    public void onClick(View v) { 
     System.out.println("ABC"); 
    } 
}); 

从drawView函数的init （），并在game_screen.xml被设置为内容视图setContentView（R.layout.game_screen）后在MainGameScreen.java中定义它;

public class MainGameScreen extends FragmentActivity { 
Bundle args = new Bundle(); 

@Override 
public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    findViewById(R.id.start_game0).setOnClickListener(new OnClickListener() { 
     @Override 
     public void onClick(View v) { 

      DialogFragment newFragment = new DialogBox(); 

      newFragment.show(getSupportFragmentManager(), "chall_diag"); 
      setContentView(R.layout.game_screen); 

      final Button button = (Button) findViewById(R.id.display_challengeX); 
      button.setOnClickListener(new View.OnClickListener() { 

       DialogFragment newFragment = new DialogBox(); 
       @Override 
       public void onClick(View v) { 
        newFragment.show(getSupportFragmentManager(), "chall_diag"); 
       } 
      }); 

     } 

    });