爲什麼我的Android應用程序無法看到數據庫文件？

Question

我正在創建一個Android應用程序，我想進行註冊。我已經將C.R.U.D的文件寫入數據庫。當我開始我的應用程序，並嘗試添加某人，我可以看到彈出與消息：

"Unfortunately , the application has been stopped". 

這裏是我的數據庫控制器代碼：

package com.example.lingwista.lingwista; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

public class DB_Controller extends SQLiteOpenHelper { 
public DB_Controller(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) { 
    super(context, "LINGWISTA.db", factory, version); 
} 

@Override 
public void onCreate(SQLiteDatabase db) { 
    db.execSQL("CREATE TABLE USERS(ID INTEGER PRIMARY KEY AUTOINCREMENT, USERNAME TEXT UNIQUE, PASSWORD TEXT);"); 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    db.execSQL("DROP TABLE IF EXISTS USERS;"); 
} 

public void insert_user(String userName, String password){ 
    ContentValues contentValues = new ContentValues(); 
    contentValues.put("USERNAME",userName); 
    contentValues.put("PASSWORD",password); 
    this.getWritableDatabase().insertOrThrow("USERS", "", contentValues); 
} 


public boolean search_user(String userName){ 
    Cursor cursor = this.getReadableDatabase().rawQuery("SELECT USERNAME FROM USERS",null); 
    while (cursor.moveToNext()){ 
     if(cursor.getString(1).equals(userName)){ 
      return true; 
     } 
    } 
    return false; 
} 

public boolean search_password(String password){ 
    Cursor cursor = this.getReadableDatabase().rawQuery("SELECT PASSWORD FROM USERS",null); 
    while (cursor.moveToNext()){ 
     if(cursor.getString(1).equals(password)){ 
      return true; 
     } 
    } 
    return false; 
} 

}

這是java我使用控制器的文件：

package com.example.lingwista.lingwista; 

import android.content.Context; 
import android.content.Intent; 
import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.widget.EditText; 
import android.widget.Toast; 

public class Rejestracja extends AppCompatActivity { 
DB_Controller controller; 
EditText username; 
EditText password1; 
EditText password2; 
String login; 
String haslo1; 
String haslo2; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_rejestracja); 
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 
    username = (EditText)findViewById(R.id.editText3); 
    password1 = (EditText)findViewById(R.id.editText4); 
    password2 = (EditText)findViewById(R.id.editText5); 
    controller = new DB_Controller(this, "", null, 1); 
} 

public void goToMenu(View view) { 
    login = username.getText().toString(); 
    haslo1 = password1.getText().toString(); 
    haslo2 = password2.getText().toString(); 

    boolean u; 

    String message; 
    Context context = getApplicationContext(); 
    int duration = Toast.LENGTH_SHORT; 

    if(haslo1.equals(haslo2)){ 
     u = controller.search_user(login); 

     if(u==true){ 
      message = "Istnieje już użytkownik który korzysta z tego adresu email"; 
      Toast toast = Toast.makeText(context,message, duration); 
      toast.show(); 
     } 
     else{ 
      controller.insert_user(login,haslo1); 
      Intent intent = new Intent(".Menu"); 
      startActivity(intent); 
     } 


    }else{ 
     message = "Błąd hasła. Proszę upewnić się ze oba pola zawierają to samo hasło"; 
     Toast toast = Toast.makeText(context,message, duration); 
     toast.show(); 
    } 
    if(login.equals("") || haslo1.equals("") || haslo2.equals("")){ 
     message = "Wszystkie pola muszą być wypełnione !"; 
     Toast toast = Toast.makeText(context,message, duration); 
     toast.show(); 
    } 
} 

@Override 
public void onPause(){ 
    super.onPause(); 
    finish(); 
} 

public void back(View view) { 
    Intent intent =new Intent(".MainMenuActivity"); 
    startActivity(intent); 
} 

public void exitApp(View view) { 
    System.exit(0); 
} 
} 

這是我的content.xml：

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
app:layout_behavior="@string/appbar_scrolling_view_behavior" 
tools:context="com.example.lingwista.lingwista.Rejestracja" 
tools:showIn="@layout/activity_rejestracja"> 

<ImageView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/imageView2" 
    android:layout_alignParentTop="true" 
    android:src="@drawable/lingwista" 
    android:layout_centerHorizontal="true" /> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:textAppearance="?android:attr/textAppearanceLarge" 
    android:text="Rejestracja" 
    android:id="@+id/textView3" 
    android:layout_below="@+id/imageView2" 
    android:layout_centerHorizontal="true" 
    android:textColor="#00FF00" 
    android:layout_marginTop="30dp" 
    android:textSize="38dp" /> 

<EditText 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:inputType="textEmailAddress" 
    android:ems="10" 
    android:id="@+id/editText3" 
    android:layout_below="@+id/textView3" 
    android:layout_marginTop="10dp" 
    android:layout_centerHorizontal="true" 
    android:autoText="false" 
    android:hint="Adres email" 
    android:backgroundTint="#0000ff" /> 

<EditText 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:inputType="textPassword" 
    android:ems="10" 
    android:id="@+id/editText4" 
    android:layout_below="@+id/editText3" 
    android:layout_marginTop="5dp" 
    android:layout_centerHorizontal="true" 
    android:hint="Hasło" 
    android:backgroundTint="#0000ff" /> 

<EditText 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:inputType="textPassword" 
    android:ems="10" 
    android:id="@+id/editText5" 
    android:layout_below="@+id/editText4" 
    android:layout_alignRight="@+id/editText4" 
    android:layout_marginTop="5dp" 
    android:layout_alignEnd="@+id/editText4" 
    android:hint="Powtorz hasło" 
    android:backgroundTint="#0000ff" /> 

<Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="Zarejestruj" 
    android:id="@+id/button12" 
    android:layout_marginTop="52dp" 
    android:layout_below="@+id/editText5" 
    android:layout_centerHorizontal="true" 
    android:textColor="#ffffff" 
    android:textSize="20dp" 
    android:background="#0000ff" 
    android:onClick="goToMenu"/> 
</RelativeLayout> 

這是錯誤日誌：

01-16 02:55:10.539 18767-18791/com.example.lingwista.lingwista E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab855e50 
01-16 02:55:13.104 18767-18767/com.example.lingwista.lingwista E/CursorWindow: Failed to read row 0, column 1 from a CursorWindow which has 1 rows, 1 columns. 
01-16 02:55:13.104 18767-18767/com.example.lingwista.lingwista D/AndroidRuntime: Shutting down VM 
01-16 02:55:13.104 18767-18767/com.example.lingwista.lingwista E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.example.lingwista.lingwista, PID: 18767 
java.lang.IllegalStateException: Could not execute method for android:onClick 
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:275) 
at android.view.View.performClick(View.java:5198) 
at android.view.View$PerformClick.run(View.java:21147) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
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$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
Caused by: java.lang.reflect.InvocationTargetException 
at java.lang.reflect.Method.invoke(Native Method) 
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:270) 
at android.view.View.performClick(View.java:5198) 
at android.view.View$PerformClick.run(View.java:21147) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
Caused by: java.lang.IllegalStateException: Couldn't read row 0, col 1 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it. 
at android.database.CursorWindow.nativeGetString(Native Method) 
at android.database.CursorWindow.getString(CursorWindow.java:438) 
at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:51) 
at com.example.lingwista.lingwista.DB_Controller.search_user(DB_Controller.java:35) 
at com.example.lingwista.lingwista.Rejestracja.goToMenu(Rejestracja.java:47) 
at java.lang.reflect.Method.invoke(Native Method) 
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:270) 
at android.view.View.performClick(View.java:5198) 
at android.view.View$PerformClick.run(View.java:21147) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
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) 
01-16 02:55:19.507 18767-18767/? I/Process: Sending signal. PID: 18767 SIG: 9 

Answer 1

的錯誤是明顯的：

Caused by: java.lang.IllegalStateException: Couldn't read row 0, col 1 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it. 
at android.database.CursorWindow.nativeGetString(Native Method) 
at android.database.CursorWindow.getString(CursorWindow.java:438) 
at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:51) 
at com.example.lingwista.lingwista.DB_Controller.search_user(DB_Controller.java:35) 

這裏是一個的崩潰違規代碼：

public boolean search_user(String userName){ 
    Cursor cursor = this.getReadableDatabase().rawQuery("SELECT USERNAME FROM USERS",null); 
    while (cursor.moveToNext()){ 
     if(cursor.getString(1).equals(userName)){ 
      return true; 
     } 
    } 
    return false; 
} 

列有從零開始的索引，你只需要在你的一列查詢。因此它應該是cursor.getString(0)

Cursor.getString(int columnIndex) documentation：

返回請求的列作爲一個字符串的值。

結果以及在列值爲空或列類型不是字符串類型時此方法是否引發異常是實現定義的。

參數

columnIndex - 目標列的基於零的索引。

返回

該列作爲字符串的值。

另請注意，即使您使用了正確的列，也可以獲得空引用。你可能想是這樣的：

if (!cursor.isNull(0) && cursor.getString(0).equals(userName)) {