語境問題（android.view.ContextThemeWrapper不能轉換到android.app.Activity）

Question

我下面就SQLite的本教程：https://www.youtube.com/watch?v=3k3CunDZpFk&list=PLshdtb5UWjSrEUEKlfHwqQtYu2HxtCwu_&index=8

我試圖做他做了什麼，而是從分段。我無法理解所得到的上下文錯誤。任何人都可以解釋給我嗎？

如果您需要更多信息，請不要猶豫，問。

謝謝你的時間。

10-18 17:33:16.860 7384-7384/com.example.michael.rogplayer E/AndroidRuntime﹕ FATAL EXCEPTION: main 
Process: com.example.michael.rogplayer, PID: 7384 
java.lang.ClassCastException: android.view.ContextThemeWrapper cannot be cast to android.app.Activity 
     at com.example.michael.rogplayer.BackgroundTask.<init>(BackgroundTask.java:20) 
     at com.example.michael.rogplayer.CreateNewChar_Fragment$1.onClick(CreateNewChar_Fragment.java:98) 

第20行：activity = (Activity) ctx;

線98：BackgroundTask backgroundTask = new BackgroundTask(getView().getContext());

這裏的CreateNewChar_Fragment.java

public class CreateNewChar_Fragment extends DialogFragment { 

private static Activity scanForActivity(Context cont) { 
    if (cont == null) 
     return null; 
    else if (cont instanceof Activity) 
     return (Activity)cont; 
    else if (cont instanceof ContextWrapper) 
     return scanForActivity(((ContextWrapper)cont).getBaseContext()); 

    return null; 
} 

EditText name; 
Button CANCEL, SAVE; 
String NAME; 
Context CTX; 

private static final String ARG_PARAM1 = "param1"; 
private static final String ARG_PARAM2 = "param2"; 

private String mParam1; 
private String mParam2; 

private OnFragmentInteractionListener mListener; 

public static CreateNewChar_Fragment newInstance(String param1, String param2) { 
    CreateNewChar_Fragment fragment = new CreateNewChar_Fragment(); 
    Bundle args = new Bundle(); 
    args.putString(ARG_PARAM1, param1); 
    args.putString(ARG_PARAM2, param2); 
    fragment.setArguments(args); 
    return fragment; 
} 

public CreateNewChar_Fragment() { 

} 

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

    if (getArguments() != null) { 
     mParam1 = getArguments().getString(ARG_PARAM1); 
     mParam2 = getArguments().getString(ARG_PARAM2); 
    } 


} 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 

    getDialog().setTitle("State your name!"); 

    return inflater.inflate(R.layout.fragment_create_new_char_, container, false); 

} 



public void onViewCreated(View container, Bundle savedInstanceState) { 
    super.onViewCreated(container, savedInstanceState); 

    CTX = container.getContext(); 
    SAVE = (Button) getView().findViewById(R.id.save); 
    CANCEL = (Button) getView().findViewById(R.id.cancel); 
    name = (EditText) getView().findViewById(R.id.name); 
    NAME = name.getText().toString(); 

    SAVE.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      if (TextUtils.isEmpty(name.getText())) { 
       Toast.makeText(getView().getContext(), "Are you mute!?!?! State your name!!!", 
         Toast.LENGTH_LONG).show(); 
      } else { 
       BackgroundTask backgroundTask = new BackgroundTask(getView().getContext()); 
       backgroundTask.execute("add_info", NAME); 
       getDialog().dismiss(); 
      } 
     } 
    }); 

    CANCEL.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      getDialog().dismiss(); 
     } 
    }); 
} 

public void onButtonPressed(Uri uri) { 
    if (mListener != null) { 
     mListener.onFragmentInteraction(uri); 
    } 
} 

@Override 
public void onAttach(Activity activity) { 
    super.onAttach(activity); 
    try { 
     mListener = (OnFragmentInteractionListener) activity; 
    } catch (ClassCastException e) { 
     throw new ClassCastException(activity.toString() 
       + " must implement OnFragmentInteractionListener"); 
    } 
} 

@Override 
public void onDetach() { 
    super.onDetach(); 
    mListener = null; 
} 

public interface OnFragmentInteractionListener { 
    public void onFragmentInteraction(Uri uri); 
} 
} 

這裏的BackgroundTask.java

public class BackgroundTask extends AsyncTask <String,CharacterDisplay,String> { 

Context ctx; 
CharacterAdapter characterAdapter; 
Activity activity; 
ListView listView; 
BackgroundTask(Context ctx) { 
    this.ctx = ctx; 
    activity = (Activity) ctx; 
} 

@Override 
protected void onPreExecute() { 
    super.onPreExecute(); 
} 

@Override 
protected String doInBackground(String... params) { 
    String method = params[0]; 
    DatabaseOperations databaseOperations = new DatabaseOperations(ctx); 

    if (method.equals("add_info")) { 
     String name = params[1]; 
     SQLiteDatabase db = databaseOperations.getWritableDatabase(); 
     databaseOperations.putInfo(db, name); 
     return "One row inserted"; 

    } else if (method.equals("get_info")) { 
     listView = (ListView) activity.findViewById(R.id.char_list); 
     SQLiteDatabase db = databaseOperations.getReadableDatabase(); 
     Cursor cursor = databaseOperations.getInfo(db); 
     characterAdapter = new CharacterAdapter(ctx, R.layout.display_character_row); 
     String name; 
     while (cursor.moveToNext()) { 
      name = cursor.getString(cursor.getColumnIndex(TableData.TableInfo.NAME)); 
      CharacterDisplay characterDisplay = new CharacterDisplay(name); 
      publishProgress(characterDisplay); 
     } 
     return "get_info"; 
    } 
    return null; 
} 

@Override 
protected void onProgressUpdate(CharacterDisplay... values) { 
    characterAdapter.add(values[0]); 
} 

@Override 
protected void onPostExecute(String result) { 
    if (result.equals("get_info")) { 
     listView.setAdapter(characterAdapter); 
    } else { 
     Toast.makeText(ctx,result, Toast.LENGTH_LONG).show(); 
    } 

} 
} 

這裏的CharacterDisplay.java

public class CharacterDisplay { 

private String name; 

public CharacterDisplay(String name) { 
    this.setName(name); 
} 

public String getName() { 
    return name; 
} 

public void setName(String name) { 
    this.name = name; 
} 
} 

這裏的CharacterAdapter.java

public class CharacterAdapter extends ArrayAdapter { 
List list = new ArrayList(); 

public CharacterAdapter(Context context, int resource) { 
    super(context, resource); 
} 

public void add(Character object) { 
    list.add(object); 
    super.add(object); 
} 

@Override 
public int getCount() { 
    return list.size(); 
} 

@Override 
public Object getItem(int position) { 
    return list.get(position); 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    View row = convertView; 
    CharacterHolder characterHolder; 
    if(row == null) { 
     LayoutInflater layoutInflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     row = layoutInflater.inflate(R.layout.display_character_row, parent, false); 
     characterHolder = new CharacterHolder(); 
     characterHolder.tx_name = (TextView) row.findViewById(R.id.char_name); 
     row.setTag(characterHolder); 
    } else { 
     characterHolder = (CharacterHolder) row.getTag(); 
    } 

    CharacterDisplay characterDisplay = (CharacterDisplay) getItem(position); 
    characterHolder.tx_name.setText(characterDisplay.getName().toString()); 
    return row; 
} 

static class CharacterHolder { 
    TextView tx_name; 
} 
} 

Answer 1

Activity擴展ContextThemeWrapper所以轉換異常造成，因爲你的ContextThemeWrapper不是Activity的實例。它本身可能是另一個子類或ContextThemeWrapper。

爲了得到一個片段內的Activity背景下，你可以使用的getView().getContext()getActivity()代替