來自ListView的ContextMenu的標題項目

Question

我想從ListView中的選定項目設置ContextMenu的標題。然而，每次我在模擬器上運行它，它崩潰，我必須強制關閉它。 DDMS顯示引發了未捕獲的java.lang.NullPointerException。我的DbTest.java類會出現問題嗎？我已經定義了DbTest.java類中的所有數據庫操作。

注：異常可能拋出在這條線： -

Cursor mCursor = (Cursor) getListAdapter().getItem(info.position); 

請看看我的代碼，並指出錯誤。

package com.tintin.prototype_2; 

import android.app.ListActivity; 
import android.content.Intent; 
import android.database.Cursor; 
import android.os.Bundle; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.util.Log; 
import android.view.ContextMenu; 
import android.view.ContextMenu.ContextMenuInfo; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.AdapterView; 
import android.widget.Button; 
import android.widget.ListView; 

public class Contact_LA extends ListActivity { 

DbTest db; 
SimpleCursorAdapter dataAdapter; 

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.check); 
    db = new DbTest(this); 
    displayList(); 
} 

public void onResume(){ 
    Cursor newCursor = db.getallContacts(); 
    dataAdapter.changeCursor(newCursor); 
    super.onResume(); 
} 

public void displayList(){ 
    Cursor cursor = db.getallContacts(); 
    String columns[] = new String[] {db.Name, db.Number}; 
    int to[] = new int[] {R.id.textView1, R.id.textView2}; 
    dataAdapter = new SimpleCursorAdapter(this, R.layout.check_layout, cursor, columns, to, 0); 
    //ListView lv = (ListView) findViewById(R.id.list); 
    ListView lv = getListView(); 
    lv.setAdapter(dataAdapter); 
    registerForContextMenu(lv); 

    Button b = (Button) findViewById(R.id.AddContact); 

    b.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View arg0) { 
      startActivity(new Intent(Contact_LA.this, Contact_Add.class)); 
     } 
    }); 
    db.close(); 
} 

public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo){ 
    super.onCreateContextMenu(menu, v, menuInfo); 
    AdapterView.AdapterContextMenuInfo info; 
    try{ 
     info = (AdapterView.AdapterContextMenuInfo) menuInfo; 
    }catch(ClassCastException e){ 
     Log.v("BAD", "Bad Info"); 
     return; 
    } 
    Cursor mCursor = (Cursor) getListAdapter().getItem(info.position); 
    if(mCursor == null)return; 
    menu.setHeaderTitle(mCursor.getString(mCursor.getColumnIndex("Name"))); 
    menu.add(0, v.getId(), 0, "Delete"); 
} 
} 

Answer 1

嘗試

此

try{ 
     info = menuInfo.getMenuInfo();; 
} catch(ClassCastException e){ 
     Log.v("BAD", "Bad Info"); 
     return; 
}