開始新的活動崩潰Android應用程序

Question

我已閱讀了有關此主題的幾個問題，但似乎沒有解決我的問題。當我開始一個新的Android活動時，應用程序崩潰。我懷疑它在我的佈局文件中。自從Android開始包含內容xml文件以來，我就遇到了這個問題。

這是我開始我的新活動：

private void logUserIn(User returnedUser){ 
    userLocalStore.setUserLoggedIn(true); 
    userLocalStore.storeUserData(returnedUser); 
    startActivity(new Intent(this, MainActivity.class)); 
} 

這在MainActivity.class我的OnCreate代碼中發現：我的佈局文件中

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    bJoinLeague = (Button)findViewById(R.id.bJoinLeague); 
    bJoinLeague.setOnClickListener(this); 

    bCreateLeague = (Button)findViewById(R.id.bCreateLeague); 
    bCreateLeague.setOnClickListener(this); 

    bViewLeagues = (Button)findViewById(R.id.bViewLeagues); 
    bViewLeagues.setOnClickListener(this); 

    bLogout = (Button) findViewById(R.id.bLogout); 
    bLogout.setOnClickListener(this); 

    userLocalStore = new UserLocalStore(this); 
} 

我懷疑問題出，但作爲我不熟悉Android開發新手。這裏是我的activity_main.xml中：

<?xml version="1.0" encoding="utf-8"?> 
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:fitsSystemWindows="true" 
tools:context="com.example.myname.myapp.MainActivity"> 

<include layout="@layout/content_main" /> 

</android.support.design.widget.CoordinatorLayout> 

而且我content_main.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:orientation="vertical" 
android:layout_height="match_parent" 
android:padding="10dp" 
android:layout_width="match_parent"> 

<Button 
    android:id="@+id/bCreateLeagues" 
    android:text="Create League" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" /> 

<Button 
    android:id="@+id/bJoinLeague" 
    android:text="Join League" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" /> 

<Button 
    android:id="@+id/bViewLeagues" 
    android:text="View My Leagues" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" /> 

<Button 
    android:id="@+id/bLogout" 
    android:text="Logout" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" /> 

</LinearLayout> 

我也包括在我Manifest.xml文件，這些新的活動，我已經看到了作爲解決方案几個類似的問題。這裏的Manifest.xml

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
package="com.example.myname.myapp"> 

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

<application 
    android:allowBackup="true" 
    android:icon="@mipmap/ic_launcher" 
    android:label="@string/app_name" 
    android:supportsRtl="true" 
    android:theme="@style/AppTheme"> 
    <activity 
     android:name=".MainActivity" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme.NoActionBar"> 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

      <category android:name="android.intent.category.LAUNCHER" /> 
     </intent-filter> 
    </activity> 
    <activity android:name=".Login" /> 
    <activity android:name=".Register" /> 
    <activity 
     android:name=".CreateLeague" 
     android:label="@string/title_activity_create_league" 
     android:theme="@style/AppTheme.NoActionBar" /> 
    <activity 
     android:name=".JoinLeague" 
     android:label="@string/title_activity_join_league" 
     android:theme="@style/AppTheme.NoActionBar" /> 
    <activity 
     android:name=".ViewLeagues" 
     android:label="@string/title_activity_view_leagues" 
     android:theme="@style/AppTheme.NoActionBar"></activity> 
</application> 

</manifest> 

最後，我logcat的

FATAL EXCEPTION: main 
Process: com.example.myname.myapp, PID: 3931 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myname.myapp/com.example.myname.myapp.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference 
at com.example.myname.myapp.MainActivity.onCreate(MainActivity.java:27) 
at android.app.Activity.performCreate(Activity.java:6237) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)  
at android.app.ActivityThread.-wrap11(ActivityThread.java)  
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)  
at android.os.Handler.dispatchMessage(Handler.java:102)  
at android.os.Looper.loop(Looper.java:148)  
at android.app.ActivityThread.main(ActivityThread.java:5417)  
at java.lang.reflect.Method.invoke(Native Method)  
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)  
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)  

正如我前面提到的，我認爲是錯誤的佈局文件。自從Android Studio分離content.xml和activity.xml以來，這已經成爲一個問題。

Answer 1

它看起來是由錯字造成的。

在Java代碼中，你抓住了ID bCreateLeague一個按鈕，但在XML中，按鈕與ID bCreateLeagues（注意「S」末）