空指針異常

Question

您好我有下面的代碼，我有一個空指針異常（以下文件名是Home.java）

package com.sof.android; 


import android.app.AlertDialog; 
import android.app.TabActivity; 
import android.content.DialogInterface; 
import android.content.Intent; 
import android.content.res.Resources; 
import android.os.Bundle; 
import android.view.KeyEvent; 
import android.view.Menu; 
import android.view.MenuInflater; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.Window; 
import android.widget.Button; 
import android.widget.TabHost; 
import android.widget.TextView; 
import android.widget.Toast; 

public class Home extends TabActivity { 
    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     requestWindowFeature(Window.FEATURE_CUSTOM_TITLE); 
     setContentView(R.layout.home); 
     getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.home_title); 


     TextView username = (TextView) findViewById(R.id.usernameBar); 
     username.setText(Global.username); 






     //Logout 

     Button logOut = (Button) this.findViewById(R.id.logoutBar); 
     logOut.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 

       AlertDialog.Builder builder = new AlertDialog.Builder(Home.this); 
       builder.setMessage("Are you sure you want to Log Out?") 
         .setCancelable(false) 
         .setPositiveButton("Yes", new DialogInterface.OnClickListener() { 
          public void onClick(DialogInterface dialog, int id) { 
           finish(); 
          } 
         }) 
         .setNegativeButton("No", new DialogInterface.OnClickListener() { 
          public void onClick(DialogInterface dialog, int id) { 
           dialog.cancel(); 
          } 
         }); 
       AlertDialog alert = builder.create(); 
       alert.show(); 



      } 
     }); 

     Resources res = getResources(); // Resource object to get Drawables 
     TabHost tabHost = getTabHost(); // The activity TabHost 
     TabHost.TabSpec spec; // Resusable TabSpec for each tab 
     Intent intent; // Reusable Intent for each tab 

     // Create an Intent to launch an Activity for the tab (to be reused) 
     intent = new Intent().setClass(this, a.class); 

     // Initialize a TabSpec for each tab and add it to the TabHost 
     spec = tabHost.newTabSpec("artists").setIndicator("Home", 
          res.getDrawable(R.drawable.a)) 
         .setContent(intent); 
     tabHost.addTab(spec); 

     // Do the same for the other tabs 
     intent = new Intent().setClass(this, b.class); 
     spec = tabHost.newTabSpec("albums").setIndicator("Ask", 
          res.getDrawable(R.drawable.b)) 
         .setContent(intent); 
     tabHost.addTab(spec); 

     intent = new Intent().setClass(this, c.class); 
     spec = tabHost.newTabSpec("songs").setIndicator("Questions", 
          res.getDrawable(R.drawable.c)) 
         .setContent(intent); 
     tabHost.addTab(spec); 

     intent = new Intent().setClass(this, c.class); 
     spec = tabHost.newTabSpec("tutorial").setIndicator("Tutorials", 
          res.getDrawable(R.drawable.d)) 
         .setContent(intent); 
     tabHost.addTab(spec); 

     intent = new Intent().setClass(this, e.class); 
     spec = tabHost.newTabSpec("account").setIndicator("Account", 
          res.getDrawable(R.drawable.e)) 
         .setContent(intent); 
     tabHost.addTab(spec); 
     tabHost.setCurrentTab(0); 
    } 

    public boolean onKeyDown(int keyCode, KeyEvent event) { 
     if (keyCode == KeyEvent.KEYCODE_BACK) { 

     //preventing default implementation previous to android.os.Build.VERSION_CODES.ECLAIR 
      Toast.makeText(getApplicationContext(), "Please Use Log Out.", Toast.LENGTH_LONG).show(); 
     return true; 

     } 

     return super.onKeyDown(keyCode, event);  
    } 


    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     MenuInflater inflater = getMenuInflater(); 
     inflater.inflate(R.menu.menu, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     switch (item.getItemId()) { 
      case R.id.icon:  Intent previewMessage = new Intent(getParent(), b.class); 
           TabGroupActivity parentActivity = (TabGroupActivity)getParent(); 
           parentActivity.startChildActivity("askquestion", previewMessage); 

           break; 
      case R.id.text:  AlertDialog.Builder builder = new AlertDialog.Builder(Home.this); 
           builder.setMessage("Are you sure you want to Log Out?") 
             .setCancelable(false) 
             .setPositiveButton("Yes", new DialogInterface.OnClickListener() { 
              public void onClick(DialogInterface dialog, int id) { 
               finish(); 
              } 
             }) 
             .setNegativeButton("No", new DialogInterface.OnClickListener() { 
              public void onClick(DialogInterface dialog, int id) { 
               dialog.cancel(); 
              } 
             }); 
           AlertDialog alert = builder.create(); 
           alert.show(); 
           break; 

      case R.id.icontext: Intent Account = new Intent(getParent(), e.class); 
           TabGroupActivity parentActivityE = (TabGroupActivity)getParent(); 
           parentActivityE.startChildActivity("myaccount", Account); 

           break; 
     } 
     return true; 
    } 
} 

Answer 1

使用Home.this代替的getParent（）