從android中的另一個類的主要活動調用方法

我有一個帶有文本視圖和三個圖像按鈕的列表視圖。我試圖在單擊其中一個圖像按鈕時從主頁面調用方法。但我得到這個錯誤：從android中的另一個類的主要活動調用方法

04-19 13:02:48.021 30996-30996/com.example.lama.audiotest E/AndroidRuntime: FATAL EXCEPTION: main 
                     Process: com.example.lama.audiotest, PID: 30996 
                     java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference 
                      at android.content.ContextWrapper.getResources(ContextWrapper.java:92) 
                      at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81) 
                      at android.media.MediaPlayer.create(MediaPlayer.java:1007) 
                      at android.media.MediaPlayer.create(MediaPlayer.java:990) 
                      at com.example.lama.audiotest.Main3Activity.play(Main3Activity.java:35) 
                      at com.example.lama.audiotest.CustomAdapter$1.onClick(CustomAdapter.java:83) 
                      at android.view.View.performClick(View.java:5697) 
                      at android.view.View$PerformClick.run(View.java:22526) 
                      at android.os.Handler.handleCallback(Handler.java:739) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:158) 
                      at android.app.ActivityThread.main(ActivityThread.java:7229) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

我試圖移動這條線：

mp= MediaPlayer.create(Main3Activity.this,R.raw.alfatiha);

到的onCreate（）;然後它工作，但我想播放不同的音頻，具體取決於我用play方法得到的字符串。如何解決這個問題？

我mainactivity：

public class Main3Activity extends Activity { 

private static final String TAG = Main3Activity.class.getSimpleName(); 
static MediaPlayer mp; 

/** 
* Called when the activity is first created. 
*/ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main3); 

    ListView listView = (ListView) findViewById(R.id.list_data); 

    CustomAdapter customAdapter = new CustomAdapter(); 

    listView.setAdapter(customAdapter); 

} 

public void play(String name){ 
    if (name.equals("الفاتحه")){ 
     mp= MediaPlayer.create(Main3Activity.this,R.raw.alfatiha); 
     mp.start(); 
    } 
} 

public void pause(){ 
     mp.pause(); 
} 

public void stop(){ 
    mp.stop(); 
} 
}

我的名單適配器：

public class CustomAdapter extends BaseAdapter { 
Main3Activity main= new Main3Activity(); 
private static final String TAG = CustomAdapter.class.getSimpleName(); 
ArrayList<DataModel> listArray; 

public CustomAdapter() { 
    listArray = new ArrayList<DataModel>(5); 
    listArray.add(new DataModel("الفاتحه", 5, 1.8, "Java")); 
    listArray.add(new DataModel("البقرة", 10, 2.8, "Python")); 
    listArray.add(new DataModel("ال عمران", 15, 3.8, "Django")); 

} 

@Override 
public int getCount() { 
    return listArray.size(); // total number of elements in the list 
} 

@Override 
public Object getItem(int i) { 
    return listArray.get(i); // single item in the list 
} 

@Override 
public long getItemId(int i) { 
    return i;     // index number 
} 

@Override 
public View getView(int index, View view, final ViewGroup parent) { 

    if (view == null) { 
     LayoutInflater inflater = LayoutInflater.from(parent.getContext()); 
     view = inflater.inflate(R.layout.list, parent, false); 
    } 

    final MediaPlayer mp; 


    final DataModel dataModel = listArray.get(index); 

    TextView textView = (TextView) view.findViewById(R.id.Itemname); 
    textView.setText(dataModel.getName()); 

    ImageButton play = (ImageButton) view.findViewById(R.id.btnplay); 
    ImageButton pause = (ImageButton) view.findViewById(R.id.btnpause); 
    ImageButton stop = (ImageButton) view.findViewById(R.id.btnstop); 

    play.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 


      main.play(dataModel.getName()); 
      // Toast.makeText(parent.getContext(), "you clicked play for: " + dataModel.getName(), Toast.LENGTH_SHORT).show(); 
     } 
    }); 

    pause.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 

      main.pause(); 

      // Toast.makeText(parent.getContext(), "you clicked pause for: " + dataModel.getName(), Toast.LENGTH_SHORT).show(); 
     } 
    }); 
    stop.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 

      main.stop(); 
      // Toast.makeText(parent.getContext(), "you clicked stop for: " + dataModel.getName(), Toast.LENGTH_SHORT).show(); 
     } 
    }); 



    view.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      Log.d(TAG, "string: " + dataModel.getName()); 
      Log.d(TAG, "int: " + dataModel.getAnInt()); 
      Log.d(TAG, "double: " + dataModel.getaDouble()); 
      Log.d(TAG, "otherData: " + dataModel.getOtherData()); 

      Toast.makeText(parent.getContext(), "view clicked: " + dataModel.getOtherData(), Toast.LENGTH_SHORT).show(); 
     } 
    }); 

    return view; 
} 
}

來源

2017-04-19 Lama Tatwany

在您的CustomAdapter中，您正在創建一個Main3Activity的新實例，而不是將您當前的Main3Activity實例作爲自定義適配器的參數。因此，當您嘗試訪問Main3Activity方法時，您會得到一個空指針異常。

解決你的問題修改CustomAdapter構造允許Main3Activity作爲參數：

public class CustomAdapter extends BaseAdapter { 
    Main3Activity main; 
    private static final String TAG = CustomAdapter.class.getSimpleName(); 
    ArrayList<DataModel> listArray; 

    public CustomAdapter(Main3Activity main) { 
     this.main = main; 
     listArray = new ArrayList<DataModel>(5); 
     listArray.add(new DataModel("الفاتحه", 5, 1.8, "Java")); 
     listArray.add(new DataModel("البقرة", 10, 2.8, "Python")); 
     listArray.add(new DataModel("ال عمران", 15, 3.8, "Django")); 
    }

然後，回到你的Main3Activity.class，傳遞活動實例CustomAdapter：

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main3); 
    ListView listView = (ListView) findViewById(R.id.list_data); 
    CustomAdapter customAdapter = new CustomAdapter(this); 
    listView.setAdapter(customAdapter); 
}

來源

2017-04-19 10:33:53 AlexTa

工作！非常感謝：） –

你需要能夠從適配器引用外部類。

我假設適配器是在Activity類中定義的。然後你需要做的就是直接調用這個方法，不用前綴，它會找到它。

另外，爲了清楚起見，你可以使用：

Main3Activity.this.play(xxxx)

的onClickListener內。

來源

2017-04-19 10:28:33 theblitz

在您的適配器類你正在創建一個新的Main3Activity實例，這是不同的實例，這就是爲什麼你會得到NullPointerException。你所需要做的就是下面給出的。

在適配器類中創建一個接口。

public interface ItemActionListener{ 
     void onpause(DataModel model); 
     void onStop(DataModel model); 
     void onPlay(DataModel model); 
    } 
private ItemActionListener onItemActionlListener;

這個接口在活動類像下面創建一個二傳手

public void setOnItemActionlListener(ItemActionListener onItemActionlListener) { 
      this.onItemActionlListener = onItemActionlListener; 
     }

使用這個接口。

CustomAdapter customAdapter = new CustomAdapter(); 
    customAdapter.setOnItemActionlListener(onItemActionListener); 
    listView.setAdapter(customAdapter); 


private CustomAdapter .ItemActionListener onItemActionListener=new CustomAdapter .ItemActionListener() { 


     @Override 
     public void onpause(DataModel model) { 
      //Call your pause() method written in activity class 
      pause(); 

     } 

     @Override 
     public void onStop(DataModel model) { 
      //Call your stop() method written in activity class 
      stop(); 
     } 

     @Override 
     public void onPlay(DataModel model) { 
    //Call your play() method written in activity class 
      play(); 
     } 
    }; 




In your adapter class 

pause.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 

       if(onItemActionlListener !=null){ 
       onItemActionlListener.onpause(dataModel); 

       } 



      } 
     });

來源

2017-04-19 10:47:19

從android中的另一個類的主要活動調用方法

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