Android：給出空指針的靜態選項菜單

但是，隨着第一個回答的第二個選項給了我一個空指針異常。基本上它不起作用。我錯過了什麼。以下是我的代碼文件。

非常感謝您提前。

AppSetup.java

package com.connectionmanager.app; 

import android.app.Activity; 
import android.content.Context; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.KeyEvent; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 

public class AppSetup extends Activity implements OnClickListener 
{ 
    private AcmMenu acmMenu; 
    private Context appContext; 
    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.app_setup); 

     appContext = this.getApplicationContext(); 
     Log.v("Hello","Bringing up application setup Dialog box"); 

     //Set up buttons 
     Button btnSave = (Button) findViewById(R.id.ButtonSave); 
     Button btnContinue = (Button) findViewById(R.id.ButtonContinue); 
     btnSave.setOnClickListener(this); 
     btnContinue.setOnClickListener(this); 

     this.resetLabels(); 
    } 

    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) 
    { 
     if (keyCode == KeyEvent.KEYCODE_BACK) { 
      this.finish(); 
      Log.v("Hello","Back key pressed"); 
      return true; 
     } 
     return super.onKeyDown(keyCode, event); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) 
    { 
     acmMenu = new AcmMenu(menu,this.getApplicationContext()); 
     acmMenu.inflate(); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) 
    { 
     acmMenu.onSelectedItem(item,appContext); 
     return true; 
    } 

    @Override 
    public void onClick(View arg0) { 
     // TODO Auto-generated method stub 
     if(arg0.getId() == (R.id.ButtonSave)) 
     { 
      // Save information and then finish. 
      AppDatabase db = new AppDatabase(this.getApplicationContext()); 

      db.setHostname(((EditText)findViewById(R.id.editText_hostname)).getText().toString()); 
      db.setRegistrationUrl(((EditText)findViewById(R.id.editText_registration)).getText().toString()); 
      db.setSsid(((EditText)findViewById(R.id.editText_ssid)).getText().toString()); 

      db.closeDb(); 

      this.resetLabels(); 
     } 
     if(arg0.getId() == (R.id.ButtonContinue)) 
     { 
      this.finish(); 
     } 
    } 

    private void resetLabels() 
    { 
     //Get and set existing values from the database. 
     AppDatabase db = new AppDatabase(this.getApplicationContext()); 
     Log.v("Hello","Hostname from app:" +db.getHostname()); 

     TextView hostname_current = (TextView)findViewById(R.id.lbl_hostname_current); 
     hostname_current.setText("(Current: "+db.getHostname()+")"); 
     ((EditText)findViewById(R.id.editText_hostname)).setText(db.getHostname()); 

     TextView registration_current = (TextView)findViewById(R.id.lbl_registration_current); 
     registration_current.setText("(Current: "+db.getRegistrationUrl()+")"); 
     ((EditText)findViewById(R.id.editText_registration)).setText(db.getRegistrationUrl()); 

     TextView chat_current = (TextView)findViewById(R.id.lbl_chat_current); 
     //chat_current.setText("(Current: "+db.getRegistrationUrl()+")"); 
     //((EditText)findViewById(R.id.editText_chat)).setText(db.getRegistrationUrl()); 

     TextView ssid_current = (TextView)findViewById(R.id.lbl_ssid_current); 
     ssid_current.setText("(Current: "+db.getSsid()+")"); 
     ((EditText)findViewById(R.id.editText_ssid)).setText(db.getSsid()); 

     db.closeDb(); 
    } 
}

AcmMenu.java

package com.connectionmanager.app; 

import android.app.Activity; 
import android.content.Context; 
import android.content.Intent; 
import android.util.Log; 
import android.view.Menu; 
import android.view.MenuInflater; 
import android.view.MenuItem; 

public class AcmMenu extends Activity{ 

    private Menu acmMenu; 
    private static Context classContext; 

    public AcmMenu(Menu menu, Context cont) 
    { 
     classContext = cont; 
     acmMenu = menu; 
    } 

    public void inflate() 
    { 
     if (classContext == null) 
     { 
      Log.v("Hello","Context null"); 
     } 
     else 
     { 
      MenuInflater inflater = new MenuInflater(classContext); 
      inflater.inflate(R.menu.acm_menu, acmMenu); 
     } 

    } 

    public void onSelectedItem(MenuItem item, Context con) 
    { 
     Log.v("Hello","Starting activity"); 
     Intent gotoHelpScreen = new Intent(con, Help.class); 

     try 
     { 
      startActivity(new Intent(con, NewUserAccount.class)); 
     } 
     catch (Exception e) 
     { 
      e.printStackTrace(); 
      Log.v("Hello","Exception: " + e.toString()); 
     } 


     /*/ Handle item selection 
     switch (item.getItemId()) 
     { 
     case R.id.menu_wifi: 
      toggleWifi(); 
      return true; 
     case R.id.menu_account: 
      gotoAccounts(); 
      return true; 
     case R.id.menu_help: 
      showHelp(); 
      return true; 
     default: 
      return super.onOptionsItemSelected(item); 
     }*/ 
    } 

    private void toggleWifi() 
    { 

    } 

    private void gotoAccounts() 
    { 

    } 

    private void showHelp() 
    { 

    } 
}

Help.java

package com.connectionmanager.app; 

import android.app.Activity; 
import android.os.Bundle; 

public class Help extends Activity { 

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

    } 

}

清單文件

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
     package="com.connectionmanager.app" 
     android:versionCode="1" 
     android:versionName="1.0"> 

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> 
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" /> 
<uses-permission android:name="android.permission.INTERNET" /> 

    <application android:icon="@drawable/icon" android:label="@string/app_name" android:debuggable="true"> 
     <activity android:name=".CMapp" 
        android:label="@string/app_name"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 
       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity android:name=".NewUserAccount" /> 
     <activity android:name=".FoundSavedUser" /> 
     <activity android:name=".AppSetup" /> 
     <activity android:name=".Help" /> 
    </application> 
</manifest>

堆棧跟蹤

05-27 12:07:03.930: WARN/Server(7134): Addition of the standard header "cache-control" is not allowed. Please use the equivalent property in the Restlet API. 
05-27 12:07:03.930: WARN/Server(7134): Addition of the standard header "expires" is not allowed. Please use the equivalent property in the Restlet API. 
05-27 12:07:03.961: WARN/System.err(8135): java.lang.NullPointerException 
05-27 12:07:03.961: WARN/System.err(8135):  at android.app.Activity.startActivityForResult(Activity.java:2890) 
05-27 12:07:03.961: WARN/System.err(8135):  at android.app.Activity.startActivity(Activity.java:2996) 
05-27 12:07:03.961: WARN/System.err(8135):  at com.connectionmanager.app.AcmMenu.onSelectedItem(AcmMenu.java:43) 
05-27 12:07:03.961: WARN/System.err(8135):  at com.connectionmanager.app.AppSetup.onOptionsItemSelected(AppSetup.java:61) 
05-27 12:07:03.961: WARN/System.err(8135):  at android.app.Activity.onMenuItemSelected(Activity.java:2234) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:747) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:160) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:886) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.view.menu.IconMenuView.invokeItem(IconMenuView.java:545) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.view.menu.IconMenuItemView.performClick(IconMenuItemView.java:122) 
05-27 12:07:03.970: WARN/System.err(8135):  at android.view.View$PerformClick.run(View.java:8867) 
05-27 12:07:03.970: WARN/System.err(8135):  at android.os.Handler.handleCallback(Handler.java:587) 
05-27 12:07:03.970: WARN/System.err(8135):  at android.os.Handler.dispatchMessage(Handler.java:92) 
05-27 12:07:03.970: WARN/System.err(8135):  at android.os.Looper.loop(Looper.java:143) 
05-27 12:07:03.970: WARN/System.err(8135):  at android.app.ActivityThread.main(ActivityThread.java:5068) 
05-27 12:07:03.970: WARN/System.err(8135):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-27 12:07:03.970: WARN/System.err(8135):  at java.lang.reflect.Method.invoke(Method.java:521) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858) 
05-27 12:07:03.970: WARN/System.err(8135):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
05-27 12:07:03.970: WARN/System.err(8135):  at dalvik.system.NativeStart.main(Native Method) 
05-27 12:07:03.980: VERBOSE/WindowManager(1292): Remove Window{4757e618 AtchDlg:com.connectionmanager.app/com.connectionmanager.app.AppSetup paused=false}: mSurface=Surface(name=AtchDlg:com.connectionmanager.app/com.connectionmanager.app.AppSetup, identity=1792) mExiting=false isAnimating=false app-animation=null inPendingTransaction=false mDisplayFrozen=false 
05-27 12:07:03.990: ERROR/WindowManager(1292): return in removeWindowLocked 
05-27 12:07:04.000: DEBUG/InputManagerService(1292): Window already focused, ignoring focus gain of: [email protected]

來源

2011-05-25 skaneria

什麼是logcat的錯誤消息？ – Haphazard 2011-05-25 17:06:12

這就是我得到的LogCat：05-25 19：34：53.096：VERBOSE/Hello（303）：Exception：java.lang.NullPointerException。 – skaneria 2011-05-25 19:35:16

行號是什麼？在什麼文件中？它指向哪條線？ – Haphazard 2011-05-25 19:37:07

嘗試是這樣的：

public void onSelectedItem(MenuItem item, Context con){ 
     Intent intent = new Intent(); 
     intent.setClass(con, NewUserAccount.class); 
     intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 
     con.startActivity(intent); 
     this.finish();  
    }

來源

2011-08-14 15:21:07 ktBegemot

Android：給出空指針的靜態選項菜單

回答

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