Android Eclipse FC java.lang.NullPointerException？

Question

我是Android新手。我跟着一個教程來創建一個使用PHP和MySQL的登錄屏幕......它工作了兩天前..現在當我嘗試運行該應用程序時，它給了我一個強制關閉錯誤和一個Java.lang.NullPointerException .. 。我猜這意味着什麼是不應該是空的？有人能幫助我嗎？

這是我的logcat：

12-03 11:48:06.089: D/AndroidRuntime(13538): Shutting down VM 
12-03 11:48:06.099: W/dalvikvm(13538): threadid=1: thread exiting with uncaught exception (group=0x2aac8560) 
12-03 11:48:06.099: E/AndroidRuntime(13538): FATAL EXCEPTION: main 
12-03 11:48:06.099: E/AndroidRuntime(13538): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.groupone.the.health.effect/com.groupone.the.health.effect.AndroidDashboardDesignActivity}: java.lang.NullPointerException 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1659) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1675) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.ActivityThread.access$1500(ActivityThread.java:121) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:943) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.os.Looper.loop(Looper.java:123) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.ActivityThread.main(ActivityThread.java:3701) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at java.lang.reflect.Method.invokeNative(Native Method) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at java.lang.reflect.Method.invoke(Method.java:507) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:862) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at dalvik.system.NativeStart.main(Native Method) 
12-03 11:48:06.099: E/AndroidRuntime(13538): Caused by: java.lang.NullPointerException 
12-03 11:48:06.099: E/AndroidRuntime(13538): at com.groupone.the.health.effect.AndroidDashboardDesignActivity.onCreate(AndroidDashboardDesignActivity.java:92) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
12-03 11:48:06.099: E/AndroidRuntime(13538): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1623) 
12-03 11:48:06.099: E/AndroidRuntime(13538): ... 11 more 

這裏是我的.AndroidDashboardDesignActivity：

package com.groupone.test; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 

public class AndroidDashboardDesignActivity extends Activity { 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.dashboard_layout); 

     /** 
     * Creating all buttons instances 
     * */ 
     // Dash board News feed button 
     Button btn_newsfeed = (Button) findViewById(R.id.btn_news_feed); 

     // Dash board Friends button 
     Button btn_friends = (Button) findViewById(R.id.btn_friends); 

     // Dash board Messages button 
     Button btn_messages = (Button) findViewById(R.id.btn_messages); 

     // Dash board Places button 
     Button btn_places = (Button) findViewById(R.id.btn_places); 

     // Dash board Events button 
     Button btn_events = (Button) findViewById(R.id.btn_events); 

     // Dash board Photos button 
     Button btn_photos = (Button) findViewById(R.id.btn_photos); 

     /** 
     * Handling all button click events 
     * */ 

     // Listening to News Feed button click 
     btn_newsfeed.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       // Launching News Feed Screen 
       Intent i = new Intent(getApplicationContext(), NewsFeedActivity.class); 
       startActivity(i); 
      } 
     }); 

     // Listening Friends button click 
     btn_friends.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       // Launching News Feed Screen 
       Intent i = new Intent(getApplicationContext(), AndroidFacebookConnectActivity.class); 
       startActivity(i); 
      } 
     }); 

     // Listening Messages button click 
     btn_messages.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       // Launching News Feed Screen 
       Intent i = new Intent(getApplicationContext(), MessagesActivity.class); 
       startActivity(i); 
      } 
     }); 

     // Listening to Places button click 
     btn_places.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       // Launching News Feed Screen 
       Intent i = new Intent(getApplicationContext(), MessagesActivity.class); 
       startActivity(i); 
      } 
     }); 

     // Listening to Events button click 
     btn_events.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       // Launching News Feed Screen 
       Intent i = new Intent(getApplicationContext(), MessagesActivity.class); 
       startActivity(i); 
      } 
     }); 

     // Listening to Photos button click 
     btn_photos.setOnClickListener(new View.OnClickListener() { 

      public void onClick(View view) { 
       // Launching News Feed Screen 
       Intent i = new Intent(getApplicationContext(), PhotosActivity.class); 
       startActivity(i); 
      } 
     }); 
    } 
} 

這是我的佈局：

!-- Your package folder --> 
<com.groupone.the.health.effect.DashboardLayout 
    xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:layout_weight="1" 
    android:background="#3b3b3b" > 
    <!-- News Feed Button --> 
    <Button 
     android:id="@+id/btn_news_feed" 
     style="@style/DashboardButton" 
     android:drawableTop="@drawable/healthbook" 
     android:text="Activities" /> 

    <Button 
     android:id="@+id/btn_messages" 
     style="@style/DashboardButton" 
     android:drawableTop="@drawable/mental" 
     android:text="Mental Input" /> 

    <!-- Events Button --> 
    <Button 
     android:id="@+id/btn_events" 
     style="@style/DashboardButton" 
     android:drawableTop="@drawable/graph" 
     android:text="Results" /> 

    <!-- Photos Button --> 


    <!-- Friends Button --> 
    <Button 
     android:id="@+id/btn_friends" 
     style="@style/DashboardButton" 
     android:drawableTop="@drawable/btn_facebook" 
     android:text="Facebook" /> 

    <!-- Messages Button --> 


    <!-- Places Button --> 
    <Button 
     android:id="@+id/btn_places" 
     style="@style/DashboardButton" 
     android:drawableTop="@drawable/twitter_logo" 
     android:text="Health Tweets" /> 



    <Button 
     android:id="@+id/btnLogout" 
     style="@style/DashboardButton" 
     android:drawableTop="@drawable/logout" 
     android:text="Log Out"/> 



</com.groupone.the.health.effect.DashboardLayout> 

Answer 1

Button btn_photos = (Button) findViewById(R.id.btn_photos); 

此行引起問題，因爲R.id.btn_photos按鈕ID在當前佈局xml中不存在。所以請確保您在Activity中使用正確的佈局setContentView(R.layout.dashboard_layout);