Android：Static 選項菜單提供 null 指針

Question

我正在嘗試與此處的問題相同。

Static 選項菜單

但是，按照第一個答案的第二個選項給了我一個 null 指針異常。 基本上它不起作用。 我錯過了什么。 下面是我的代碼文件。

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()
    {

    }
}

幫助.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: com.android.internal.view.IInputMethodClient$Stub$Proxy@475c3990

Answer 1

嘗試這樣的事情：

 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();      
     }