使用SQLite數據庫，並將其強制關閉用於創建數據庫

Question

類：

import android.app.Activity; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 

public class sqlite extends Activity { 
    public void sqlitetry(final SQLiteDatabase sqLiteDB) { 
     String createSql = "CREATE TABLE" + 
       "(_id integer primary key autoincrement, " + 
       "name text not null);"; 
     sqLiteDB.execSQL(createSql); 
    } 

    public void sqlinit() { 
     SQLiteDatabase db = openOrCreateDatabase("MyDatabase",MODE_PRIVATE,null); 
     db.execSQL("CREATE TABLE id note exist MyTable(username Varchar, password Varchar PRIMARY KEY);"); 
     Cursor c = db.rawQuery("Select * from MyTable", null); 
     c.moveToFirst(); 
     while(c.isAfterLast() == false) { 

     }  
    } 
} 

當我將此代碼添加到我的登錄和註冊確認的班級並啓動活動，它強制關閉：

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

    sqlite as = new sqlite(); 
    SQLiteDatabase sqLiteDB = null; 
    as.sqlitetry(sqLiteDB); 
    as.sqlinit(); 

在我的設備上安裝apk後，這顯示在logcat中：

07-18 09:51:39.875: D/AndroidRuntime(25677): Shutting down VM 
07-18 09:51:39.875: W/dalvikvm(25677): threadid=1: thread exiting with uncaught exception (group=0x40018578) 
07-18 09:51:39.882: E/AndroidRuntime(25677): FATAL EXCEPTION: main 
07-18 09:51:39.882: E/AndroidRuntime(25677): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.login1/com.example.login1.Login}: java.lang.NullPointerException 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.os.Handler.dispatchMessage(Handler.java:99) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.os.Looper.loop(Looper.java:130) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.ActivityThread.main(ActivityThread.java:3687) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at java.lang.reflect.Method.invokeNative(Native Method) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at java.lang.reflect.Method.invoke(Method.java:507) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at dalvik.system.NativeStart.main(Native Method) 
07-18 09:51:39.882: E/AndroidRuntime(25677): Caused by: java.lang.NullPointerException 
07-18 09:51:39.882: E/AndroidRuntime(25677): at com.example.login1.sqlite.sqlitetry(sqlite.java:12) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at com.example.login1.Login.onCreate(Login.java:25) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 
07-18 09:51:39.882: E/AndroidRuntime(25677): ... 11 more 

我需要把用戶在數據庫中註冊後的信息並將其提取出來以便用戶登錄，但強制關閉，我不知道該怎麼辦。誰能幫我？

Answer 1

您的sqlite類擴展了Activity。你也不用在sqlite的

onCreate方法然後你有這個

sqlite as = new sqlite(); 

你需要使用startActivity(new Intent(myintent))開始活動。

建議你學習活動。

http://developer.android.com/guide/components/activities.html

還你，如果它只是一個輔助類，這

sqlite as = new sqlite(); //sqlite class extends activity 
SQLiteDatabase sqLiteDB = null; // null value 
as.sqlitetry(sqLiteDB); 
as.sqlinit(); 

你的sqlite不需要延伸Activity。

還要檢查這個教程

http://www.androidhive.info/2011/11/android-sqlite-database-tutorial/

退房教程@的Youtube特拉維斯

http://www.youtube.com/watch?v=gEg9OdufXmM（系列112到119我猜）

Answer 2

基礎上logcat的，你可以看到這行報告實際的錯誤：

07-18 09:51:39.882: E/AndroidRuntime(25677): Caused by: java.lang.NullPointerException 

下面那行，你會看到2行是執行代碼的生成實際的錯誤堆棧：

07-18 09:51:39.882: E/AndroidRuntime(25677): at com.example.login1.sqlite.sqlitetry(sqlite.java:12) 
07-18 09:51:39.882: E/AndroidRuntime(25677): at com.example.login1.Login.onCreate(Login.java:25) 

在此基礎上，你的問題只是監守空值sqLiteDB的：

SQLiteDatabase sqLiteDB = null; 
as.sqlitetry(sqLiteDB);