nullpointerexception 및 데이터베이스가 생성되지 않습니다.

Question

나는 내 머리를 쾅쾅 대고 있습니다. 나는 이것을 알아낼 수 없다. 내가하고 싶은 일은 활동이 생성 될 때 listview에 내 SQLite 데이터베이스의 항목이 채워지는 것입니다.

어쩌면 나는 작은 것을 놓치고 있는데, 나는이 시점에서 전혀 모른다. 그리고 좌절감을 넘어서기도한다. 나는 그것이 파일 탐색기에 존재하지 않기 때문에 데이터베이스가 생성되지 않는다는 것을 안다.

package com.dd.gfit; 

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

public class DatabaseHandler extends SQLiteOpenHelper { 

    private SQLiteDatabase db; 

    // database strings 
    public static final String DATABASE_NAME = "gfit.db"; 
    public static final int DATABASE_VERSION = 1; 

    // table strings 
    public static final String TABLE_ROUTINES = "routines"; 

    // key strings 
    public static final String KEY_ROUTINES_ID = "id"; 
    public static final String KEY_ROUTINES_NAME = "name"; 

    public DatabaseHandler(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 

     // create routines table 
     db.execSQL("CREATE TABLE IF NOT EXISTS " + TABLE_ROUTINES + " (" 
        + KEY_ROUTINES_ID + " INTEGER PRIMARY KEY AUTO_INCREMENT," 
        + KEY_ROUTINES_NAME + " VARCHAR" 
        + ")"); 

     // insert test data into routines table 
     db.execSQL("INSERT INTO " + TABLE_ROUTINES + " (" + KEY_ROUTINES_NAME + ") VALUES ('Test Routine 1')"); 
     db.execSQL("INSERT INTO " + TABLE_ROUTINES + " (" + KEY_ROUTINES_NAME + ") VALUES ('Test Routine 2')"); 
     db.execSQL("INSERT INTO " + TABLE_ROUTINES + " (" + KEY_ROUTINES_NAME + ") VALUES ('Test Routine 3')"); 
     db.execSQL("INSERT INTO " + TABLE_ROUTINES + " (" + KEY_ROUTINES_NAME + ") VALUES ('Test Routine 4')"); 
     db.execSQL("INSERT INTO " + TABLE_ROUTINES + " (" + KEY_ROUTINES_NAME + ") VALUES ('Test Routine 5')"); 

    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     // do database upgrades here 
    } 

    public Cursor fetchRoutines() { 
     Cursor cursor = db.query(TABLE_ROUTINES, new String[] {KEY_ROUTINES_ID, KEY_ROUTINES_NAME}, null, null, null, null, null); 

     if (cursor != null) { 
      cursor.moveToFirst(); 
     } 

     return cursor; 
    } 

} 

여기

RoutinesActivity.java이다 : 여기서

는 DatabaseHandler.java이다

package com.dd.gfit; 

import android.os.Bundle; 
import android.app.Activity; 
import android.database.Cursor; 
import android.support.v4.app.NavUtils; 
import android.view.Menu; 
import android.view.MenuInflater; 
import android.view.MenuItem; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.SimpleCursorAdapter; 

public class RoutinesActivity extends Activity { 

    private DatabaseHandler db = new DatabaseHandler(this); 
    private Cursor cursor = db.fetchRoutines(); 

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

     // Show the Up button in the action bar. 
     getActionBar().setDisplayHomeAsUpEnabled(true); 

     // open the database and show the routines 
     db.getWritableDatabase(); 
     displayRoutines(); 
    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     MenuInflater inflater = getMenuInflater(); 
     inflater.inflate(R.menu.activity_routines, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     switch (item.getItemId()) { 
     case android.R.id.home: 
      NavUtils.navigateUpFromSameTask(this); 
      return true; 
     } 
     return super.onOptionsItemSelected(item); 
    } 

    private void displayRoutines() { 

     ListAdapter adapter = new SimpleCursorAdapter(
      this, 
      R.layout.listitem_routine, cursor, 
      new String[] { db.KEY_ROUTINES_NAME }, 
      new int[] { R.id.listitem_routine_name }); 

     ListView routineList = (ListView)findViewById(R.id.list_routines); 
     routineList.setAdapter(adapter); 
    } 

} 

여기

activity_routines.xml이다

: 여기

<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" 
    tools:context=".RoutinesActivity" > 

    <ListView 
     android:id="@+id/list_routines" 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent"   
     android:layout_margin="10dp" > 

    </ListView> 

</RelativeLayout> 

가있다 listitem_routine.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="horizontal" 
    android:gravity="center_vertical" > 

    <TextView 
     android:id="@+id/listitem_routine_name" 
     android:layout_width="0dip" 
     android:layout_height="wrap_content" 
     android:layout_weight="1" 
     android:text="@string/lorem_routine_item" 
     android:textAppearance="?android:attr/textAppearanceMedium" /> 

    <ImageView 
     android:id="@+id/button_routine_edit" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:src="@drawable/ic_action_edit" 
     android:contentDescription="@string/ic_action_edit" /> 

    <ImageView 
     android:id="@+id/button_routine_delete" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:src="@drawable/ic_action_delete" 
     android:contentDescription="@string/ic_action_delete" /> 

</LinearLayout> 

무엇이 잘못 되었나요? 또한 일단이 작업을하면 listitem_routine.xml에서 볼 수있는 것처럼 각 목록보기 항목 내에 버튼이 있습니다. 어떻게 든 KEY_ROUTINES_ID를 버튼에 전달하여 각 항목을 즉시 편집 할 수 있습니다. 누구나 사용할 수있는 자습서가 있습니까 아니면 스 니펫 만 알고 있습니까?

편집 : 다음 줄에

12-24 02:52:24.429: D/dalvikvm(783): GC_FOR_ALLOC freed 49K, 7% free 2564K/2732K, paused 68ms, total 69ms 
12-24 02:52:24.449: I/dalvikvm-heap(783): Grow heap (frag case) to 3.616MB for 1048592-byte allocation 
12-24 02:52:24.559: D/dalvikvm(783): GC_FOR_ALLOC freed 2K, 5% free 3585K/3760K, paused 110ms, total 110ms 
12-24 02:52:24.659: D/dalvikvm(783): GC_CONCURRENT freed <1K, 5% free 3585K/3760K, paused 5ms+3ms, total 102ms 
12-24 02:52:24.839: D/dalvikvm(783): GC_FOR_ALLOC freed <1K, 5% free 3585K/3760K, paused 51ms, total 51ms 
12-24 02:52:24.869: I/dalvikvm-heap(783): Grow heap (frag case) to 5.863MB for 2359312-byte allocation 
12-24 02:52:24.989: D/dalvikvm(783): GC_CONCURRENT freed 0K, 3% free 5889K/6068K, paused 24ms+33ms, total 115ms 
12-24 02:52:25.319: D/gralloc_goldfish(783): Emulator without GPU emulation detected. 
12-24 02:52:31.950: E/Trace(827): error opening trace file: No such file or directory (2) 
12-24 02:52:32.660: D/dalvikvm(827): GC_FOR_ALLOC freed 52K, 7% free 2564K/2736K, paused 25ms, total 28ms 
12-24 02:52:32.670: I/dalvikvm-heap(827): Grow heap (frag case) to 3.616MB for 1048592-byte allocation 
12-24 02:52:32.710: D/dalvikvm(827): GC_FOR_ALLOC freed 2K, 5% free 3585K/3764K, paused 40ms, total 40ms 
12-24 02:52:32.760: D/dalvikvm(827): GC_CONCURRENT freed <1K, 5% free 3585K/3764K, paused 5ms+3ms, total 50ms 
12-24 02:52:32.840: D/dalvikvm(827): GC_FOR_ALLOC freed <1K, 5% free 3585K/3764K, paused 19ms, total 19ms 
12-24 02:52:32.860: I/dalvikvm-heap(827): Grow heap (frag case) to 5.863MB for 2359312-byte allocation 
12-24 02:52:33.000: D/dalvikvm(827): GC_CONCURRENT freed 0K, 4% free 5889K/6072K, paused 77ms+13ms, total 140ms 
12-24 02:52:33.250: D/gralloc_goldfish(827): Emulator without GPU emulation detected. 
12-24 02:52:36.120: D/AndroidRuntime(827): Shutting down VM 
12-24 02:52:36.140: W/dalvikvm(827): threadid=1: thread exiting with uncaught exception (group=0x40a70930) 
12-24 02:52:36.190: E/AndroidRuntime(827): FATAL EXCEPTION: main 
12-24 02:52:36.190: E/AndroidRuntime(827): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.dd.gfit/com.dd.gfit.RoutinesActivity}: java.lang.NullPointerException 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.ActivityThread.access$600(ActivityThread.java:141) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.os.Looper.loop(Looper.java:137) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.ActivityThread.main(ActivityThread.java:5039) 
12-24 02:52:36.190: E/AndroidRuntime(827): at java.lang.reflect.Method.invokeNative(Native Method) 
12-24 02:52:36.190: E/AndroidRuntime(827): at java.lang.reflect.Method.invoke(Method.java:511) 
12-24 02:52:36.190: E/AndroidRuntime(827): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
12-24 02:52:36.190: E/AndroidRuntime(827): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
12-24 02:52:36.190: E/AndroidRuntime(827): at dalvik.system.NativeStart.main(Native Method) 
12-24 02:52:36.190: E/AndroidRuntime(827): Caused by: java.lang.NullPointerException 
12-24 02:52:36.190: E/AndroidRuntime(827): at com.dd.gfit.DatabaseHandler.fetchRoutines(DatabaseHandler.java:51) 
12-24 02:52:36.190: E/AndroidRuntime(827): at com.dd.gfit.RoutinesActivity.<init>(RoutinesActivity.java:17) 
12-24 02:52:36.190: E/AndroidRuntime(827): at java.lang.Class.newInstanceImpl(Native Method) 
12-24 02:52:36.190: E/AndroidRuntime(827): at java.lang.Class.newInstance(Class.java:1319) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.Instrumentation.newActivity(Instrumentation.java:1054) 
12-24 02:52:36.190: E/AndroidRuntime(827): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097) 
12-24 02:52:36.190: E/AndroidRuntime(827): ... 11 more 

Answer 1

private DatabaseHandler db = new DatabaseHandler(this); 
private Cursor cursor = db.fetchRoutines(); 

아직 onCreate()를 호출하지 않았기 때문에이 작업을 호출 할 수 없습니다) (다음

private DatabaseHandler db; 


    @Override 
     protected void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setContentView(R.layout.activity_routines); 
    db = new DatabaseHandler(this); 

     } 

은 또한에서 onCreate에 다음 줄을 이동 마십시오. db.fetchRoutines();는 db에서 무언가를 호출합니다. 하지만 db 객체를 만들었습니다. 객체가 아직 구성되지 않았으므로 'this'를 사용할 수 없습니다.

private DatabaseHandler db = null; 
    private Cursor cursor = null; 
@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_routines); 

     // Show the Up button in the action bar. 
     getActionBar().setDisplayHomeAsUpEnabled(true); 

     // open the database and show the routines 
     db = new DatabaseHandler(this); 
     db.getWritableDatabase(); 

     cursor = db.fetchRoutines(); 
     displayRoutines(); 
    } 

이 방법

db = new DatabaseHandler(this); 

는 개체를 만들 수있는 곳입니다.

db.getWritableDatabase(); 

은 db를 얻는 곳으로,이 행 다음에 db 조작 만 사용할 수 있습니다.

Answer 2

this 키워드가 충돌하는 이유입니다 : 여기

로그입니다. 개체 생성 전에 'this'키워드를 사용하고 있습니다.

private DatabaseHandler db = new DatabaseHandler(this); 

는

private Cursor cursor = db.fetchRoutines(); 

Answer 3

DatabaseHandler에는 db 값을 할당하지 마십시오. 따라서 에서 db.query()으로 전화하면 충돌이 발생합니다.

db 멤버 변수를 설정해야 나중에 사용할 수 있습니다. DatabaseHandler.onCreate() 끝에 다음 줄을 추가하십시오.

this.db = db;