錯誤解釋

Question

這是我的錯誤：

08-07 13:50:31.175: E/AndroidRuntime(1033): FATAL EXCEPTION: main 
08-07 13:50:31.175: E/AndroidRuntime(1033): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.database_demo/com.database_demo.LoginActivity}: java.lang.NullPointerException 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.ActivityThread.access$600(ActivityThread.java:140) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.os.Handler.dispatchMessage(Handler.java:99) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.os.Looper.loop(Looper.java:137) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.ActivityThread.main(ActivityThread.java:4898) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at java.lang.reflect.Method.invokeNative(Native Method) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at java.lang.reflect.Method.invoke(Method.java:511) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at dalvik.system.NativeStart.main(Native Method) 
08-07 13:50:31.175: E/AndroidRuntime(1033): Caused by: java.lang.NullPointerException 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at com.database_demo.LoginActivity.onCreate(LoginActivity.java:92) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.Activity.performCreate(Activity.java:5206) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064) 
08-07 13:50:31.175: E/AndroidRuntime(1033):  ... 11 more 

我能辨認出這些錯誤是什麼，他們是因爲使用OnCreate()方法內聯網相關的任務！我是正確的還是可能有更多的理由呢？

清單：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
     package="com.database_demo" 
     android:versionCode="1" 
     android:versionName="1.0"> 
    <uses-sdk android:minSdkVersion="8" /> 
    <uses-permission android:name="android.permission.INTERNET" />  
    <application android:icon="@drawable/icon" android:label="@string/app_name"> 
     <activity android:name=".DashboardActivity" 
        android:label="@string/app_name"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 
       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     <!-- Control Database connection --> 
     </activity> 
     <activity android:name=".Database_demo" 
        android:label="Login"></activity> 
     <!-- DashBoard Activity --> 
     <activity 
      android:label="Dash Board" 
      android:name=".LoginActivity"></activity> 
    </application> 


</manifest> 

Answer 1

您忘記爲Button btnLinkToRegister;

btnLinkToRegister = (Button) findViewById(R.id.btnRegister); 

你必須登記參加的Manifest.xml活動文件

Answer 2

您還沒有更新你的mainfest文件，添加如下因素線AndroidManifest.xml中，它應該工作的罰款。

<activity android:name="com.database_demo.LoginActivity" />