使用游标从数据库中检索数据。

我试图从数据库中读取数据，使用HashMap但每次我在仿真器中运行程序时都会触发。我试着用** BasicNameValuePair *来检索数据，但是这也没有解决。这里是我读取数据的代码。使用游标从数据库中检索数据。

DatabaseHandler databaseHandler = new DatabaseHandler(
     getApplicationContext()); 
HashMap<String, String> user = new HashMap<String, String>(); 
user = databaseHandler.userDetails(); 

email = user.get("email").toString(); 
password = user.get("password").toString();

这里是我为userDetails（）方法

public HashMap<String, String> userDetails() { 

     HashMap<String, String> user = new HashMap<String, String>(); 
     String query = "SELECT * FROM login"; 
     SQLiteDatabase db = this.getReadableDatabase(); 
     Cursor cursor = db.rawQuery(query, null); 
     // move to first row 
     cursor.moveToFirst(); 

     if (cursor.getCount() > 0) { 
      user.put("email", cursor.getString(1)); 
      user.put("password", cursor.getString(2)); 
     } 
     cursor.close(); 
     db.close(); 
     return user; 

    }

logcat的是显示错误

07-16 17:13:23.272: E/AndroidRuntime(1396):  at com.ved_main.mainpage.VerifyMainActivity.onCreate(VerifyMainActivity.java:56) 
07-16 17:54:10.332: E/AndroidRuntime(1501): FATAL EXCEPTION: main 
07-16 17:54:10.332: E/AndroidRuntime(1501): Process: com.ved_main.mainpage, PID: 1501 
07-16 17:54:10.332: E/AndroidRuntime(1501): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ved_main.mainpage/com.ved_main.mainpage.VerifyMainActivity}: java.lang.NullPointerException 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.ActivityThread.access$800(ActivityThread.java:135) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.os.Handler.dispatchMessage(Handler.java:102) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.os.Looper.loop(Looper.java:136) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.ActivityThread.main(ActivityThread.java:5017) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at java.lang.reflect.Method.invoke(Method.java:515) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at dalvik.system.NativeStart.main(Native Method) 
07-16 17:54:10.332: E/AndroidRuntime(1501): Caused by: java.lang.NullPointerException 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at com.ved_main.mainpage.VerifyMainActivity.onCreate(VerifyMainActivity.java:54) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.Activity.performCreate(Activity.java:5231) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159) 
07-16 17:54:10.332: E/AndroidRuntime(1501):  ... 11 more

来源

2014-07-16 vishu

'VerifyMainActivity.java：54'请发送由上述活动的第54行组成的代码块。 – 0x5f3759df

第54行是相同的'email = user.get（“email”）。toString（）;'我写上面 – vishu

你必须检查用户在从它获取“email”值之前是否为空。 – joao2fast4u

表没有任何行，所以在user没有email进入目的。

来源

2014-07-17 07:33:52

使用游标从数据库中检索数据。

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