java.lang.runtimeexception：無法啓動活動componentinfo {}：java.lang.nullpointexception

Question

我創建了一個類和活動，只需要用戶填寫表單並將其存儲在數據庫中，但我收到空指針異常。我查了不少類似的帖子，但似乎沒有解決我的問題。請讓我知道我在這裏做錯了什麼。

非常感謝您的時間和考慮。

這裏是我的活動：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
tools:context=".Splash" 
><!-- android:background="@drawable/erc"--> 

<EditText 
    android:id="@+id/prayerRequestEditText" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentLeft="true" 
    android:layout_alignParentTop="true" 
    android:layout_marginLeft="30dp" 
    android:layout_marginTop="10dp" 
    android:ems="10" 
    android:hint="@string/prayer_request" 
    android:inputType="textMultiLine" > 
    <requestFocus /> 
</EditText> 

<EditText 
    android:id="@+id/prayForEditText" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/prayerRequestEditText" 
    android:layout_below="@+id/prayerRequestEditText" 
    android:layout_marginTop="30dp" 
    android:ems="10" 
    android:hint="@string/pray_for" /> 

<TextView 
    android:id="@+id/confidentialTextView" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/prayForEditText" 
    android:layout_below="@+id/prayForEditText" 
    android:layout_marginTop="30dp" 
    android:text="@string/confidential" 
    android:textAppearance="?android:attr/textAppearanceSmall" /> 

<Switch 
    android:id="@+id/confidentialSwitch" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignBottom="@+id/confidentialTextView" 
    android:layout_alignRight="@+id/prayForEditText" 
    android:textOff="@string/no" 
    android:textOn="@string/yes" /> 

<TextView 
    android:id="@+id/anonymousTextView" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignRight="@+id/confidentialTextView" 
    android:layout_below="@+id/confidentialTextView" 
    android:layout_marginTop="30dp" 
    android:text="@string/anonymous" 
    android:textAppearance="?android:attr/textAppearanceSmall" /> 

<Switch 
    android:id="@+id/anonymousSwitch" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignBaseline="@+id/anonymousTextView" 
    android:layout_alignBottom="@+id/anonymousTextView" 
    android:layout_alignRight="@+id/confidentialSwitch" 
    android:textOff="@string/no" 
    android:textOn="@string/yes" /> 

<Button 
    android:id="@+id/sendRequestButton" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@+id/anonymousTextView" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="30dp" 
    android:onClick="sendRequest" 
    android:text="@string/send_request" /> 

這裏是我的類：

package com.eastridgetoday.prayerrequest; 
    import android.app.Activity; 
    import android.content.ContentValues; 
    import android.database.sqlite.SQLiteDatabase; 
    import android.os.Bundle; 
    import android.view.View; 
    import android.widget.EditText; 

    public class PrayerRequest extends Activity{ 
SQLiteDatabase db; 
DbHelper dbHelper; 

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState);   
     setContentView(R.layout.activity_prayerrequest); 
     dbHelper = new DbHelper(this); 
     db = dbHelper.getWritableDatabase();   
     } 

public void sendRequest(View view){ 
    String prayers_request, pray_for, confidential, anonymous; 

    EditText prayers_requestET = (EditText) view.findViewById(R.id.prayerRequestEditText); 
    EditText pray_forET = (EditText) view.findViewById(R.id.prayForEditText); 
    EditText confidentialET = (EditText) view.findViewById(R.id.confidentialSwitch); 
    EditText anonymousET = (EditText) view.findViewById(R.id.anonymousSwitch); 

    prayers_request = prayers_requestET.getText().toString(); 
    pray_for = pray_forET.getText().toString(); 
    confidential = confidentialET.getText().toString(); 
    anonymous = anonymousET.getText().toString(); 

    ContentValues cv = new ContentValues(); 
    cv.put(DbHelper.PRAYER_REQUEST, prayers_request); 
    cv.put(DbHelper.PRAY_FOR, pray_for); 
    cv.put(DbHelper.CONFIDENTIAL, confidential); 
    cv.put(DbHelper.ANONYMOUS, anonymous); 

    db.insert(DbHelper.TABLE_NAME, null, cv); 
} 

}

我飛濺活動作爲我的發射活動，並祈禱申請表應該在飛濺顯示3秒後彈出。 這裏是我的清單：

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

<uses-sdk 
    android:minSdkVersion="14" 
    android:targetSdkVersion="17" /> 

<application 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
     android:name="com.eastridgetoday.prayerrequest.Splash" 
     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="com.eastridgetoday.prayerrequest.PrayerRequest" 
     android:label="@string/app_name" > 

    </activity> 
</application> 

這裏是我的控制檯：

[2013-05-31 12:04:07 - EastridgePrayerRequest] ------------------------------ 
[2013-05-31 12:04:07 - EastridgePrayerRequest] Android Launch! 
[2013-05-31 12:04:07 - EastridgePrayerRequest] adb is running normally. 
[2013-05-31 12:04:07 - EastridgePrayerRequest] Performing  com.eastridgetoday.prayerrequest.Splash activity launch 
[2013-05-31 12:04:07 - EastridgePrayerRequest] Automatic Target Mode: using existing emulator 'emulator-5554' running compatible AVD 'AVD_for_Nexus_S_by_Google' 
[2013-05-31 12:04:07 - EastridgePrayerRequest] Uploading EastridgePrayerRequest.apk onto device 'emulator-5554' 
[2013-05-31 12:04:20 - EastridgePrayerRequest] Installing EastridgePrayerRequest.apk... 
[2013-05-31 12:04:39 - EastridgePrayerRequest] Success! 
[2013-05-31 12:04:39 - EastridgePrayerRequest] Starting activity  com.eastridgetoday.prayerrequest.Splash on device emulator-5554 
[2013-05-31 12:04:43 - EastridgePrayerRequest] ActivityManager: Starting: Intent {  act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER]  cmp=com.eastridgetoday.prayerrequest/.Splash } 

這裏是我的日誌：

05-31 01:16:45.353: E/Trace(3070): error opening trace file: No such file or directory (2) 
    05-31 01:16:52.834: E/AndroidRuntime(3070): FATAL EXCEPTION: main 
    05-31 01:16:52.834: E/AndroidRuntime(3070): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.eastridgetoday.prayerrequest/com.eastridgetoday.prayerrequest.PrayerRequest}: java.lang.NullPointerException 
    05-31 01:16:52.834: E/AndroidRuntime(3070): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
    05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
    05-31 01:16:52.834: E/AndroidRuntime(3070): at android.app.ActivityThread.access$600(ActivityThread.java:141) 
    05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.os.Handler.dispatchMessage(Handler.java:99) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.os.Looper.loop(Looper.java:137) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at java.lang.reflect.Method.invoke(Method.java:511) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at dalvik.system.NativeStart.main(Native Method) 
05-31 01:16:52.834: E/AndroidRuntime(3070): Caused by: java.lang.NullPointerException 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at com.eastridgetoday.prayerrequest.DbHelper.onCreate(DbHelper.java:35) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at com.eastridgetoday.prayerrequest.PrayerRequest.onCreate(PrayerRequest.java:20) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.app.Activity.performCreate(Activity.java:5104) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
05-31 01:16:52.834: E/AndroidRuntime(3070):  ... 11 more 

這裏是我的DbHelper類：

package com.eastridgetoday.prayerrequest; 
    import android.content.Context; 
    import android.database.sqlite.SQLiteDatabase; 
    import android.database.sqlite.SQLiteOpenHelper; 

    public class DbHelper extends SQLiteOpenHelper { 

SQLiteDatabase db; 

public static final String DATABASE_NAME = "prayersdb"; 
public static final String TABLE_NAME = "prayers_table"; 
public static final String P_ID = "_id"; 
public static final String PRAYER_REQUEST = "prayers"; 
public static final String PRAY_FOR = "pray_for"; 
public static final String CONFIDENTIAL = "confidential"; 
public static final String ANONYMOUS = "anonymous"; 
public static final int VERSION = 1; 

public final String createTable = 
     "create table if not exists " + TABLE_NAME + " (" 
     + P_ID + " integer primary key autoincrement " 
     + PRAYER_REQUEST + " text " 
     + PRAY_FOR + " text " 
     + CONFIDENTIAL +" text " 
     + ANONYMOUS + " text);"; 

public DbHelper (Context context){ 
    super(context, DATABASE_NAME, null, VERSION); 

} 

@Override 
public void onCreate(SQLiteDatabase arg0) { 
    db.execSQL(createTable); 

} 

@Override 
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) { 
    db.execSQL("drop table " + TABLE_NAME); 

} 

}

Answer 1

的問題是在DbHelper類：

@Override 
public void onCreate(SQLiteDatabase arg0) { 
    db.execSQL(createTable); 
} 

db爲空，則必須對其進行初始化。