清除共享首选项将引发空指针异常

Question

每次用户从选项菜单中选择"注销" (R.Id.logout)时，我都会得到空指针异常。我不知道我没有初始化什么

@Override
        public boolean onOptionsItemSelected(MenuItem item)
        {
            switch (item.getItemId())
            {
                case R.id.settings:             
                    return false;
                case R.id.about:
                    this.startActivity(new Intent(this, About.class));
                    return true;
                case R.id.logout:
                    AlertDialog.Builder alertbox = new AlertDialog.Builder(this);
                    alertbox.setTitle("Logout");
                    alertbox.setMessage("Logging out will remove your credentials from this phone. nDo you want to logout?");
                    alertbox.setPositiveButton("Yes", new DialogInterface.OnClickListener() 
                    {                   
                        public void onClick(DialogInterface dialog, int id) 
                        {
                            Editor e = loginPref.edit();
                            e.clear();
                            Homepage.this.startActivity(new Intent(getApplicationContext(), Login.class));
                            Homepage.this.finish();             
                        }
                    });
                    alertbox.setNegativeButton("No", new DialogInterface.OnClickListener()
                    {                   
                        public void onClick(DialogInterface dialog, int id) 
                        {
                            dialog.cancel();                    
                        }
                    });
                    AlertDialog alert = alertbox.show();
                    return true;
            }
            return false;
        }

logCat

08-16 10:09:49.705: ERROR/AndroidRuntime(1531): FATAL EXCEPTION: main
08-16 10:09:49.705: ERROR/AndroidRuntime(1531): java.lang.NullPointerException
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at org.*****.android.Homepage$1.onClick(Homepage.java:79)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:158)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at android.os.Looper.loop(Looper.java:123)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at android.app.ActivityThread.main(ActivityThread.java:4627)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at java.lang.reflect.Method.invokeNative(Native Method)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at java.lang.reflect.Method.invoke(Method.java:521)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-16 10:09:49.705: ERROR/AndroidRuntime(1531):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

这很简单。在主页。java的第79行是空的。请检查这是哪一行，并发布它或发布完整的代码，包名和所有的东西，这样我们就可以帮助，因为现在我们只能猜测什么是空的。

我的第一个猜测是loginPref:

  Editor e = loginPref.edit();

是否初始化了loginPref?