0

我正把头从桌子上撞下来。我似乎无法弄清楚这一点。我要做的就是在创建活动时使用我的 SQLite 数据库中的项目填充列表视图。

也许我错过了一些小东西，我现在不知道并且非常沮丧。我知道数据库没有被创建，因为它不存在于文件资源管理器中。

这是DatabaseHandler.java：

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;
    }

}

这是 RoutinesActivity.java：

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);
    }

}

这是activity_routines.xml：

<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>

这是 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>

这里有什么问题？此外，一旦我开始工作，每个列表视图项中都有按钮，您可以通过 listitem_routine.xml 看到。我想以某种方式将 KEY_ROUTINES_ID 传递到按钮中，以便可以即时编辑每个项目。有没有我可以使用任何人都知道的教程，或者只是一个片段？

编辑：

这是日志：

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
4

3 回答 3

1

this以下行中的关键字是您崩溃的原因。您在创建对象之前使用了“this”关键字。

 private DatabaseHandler db = new DatabaseHandler(this);

请执行下列操作

private DatabaseHandler db;   


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

        }

还将以下行移至 onCreate()

private Cursor cursor = db.fetchRoutines();
于 2012-12-24T02:56:00.793 回答
1 
private DatabaseHandler db = new DatabaseHandler(this);
private Cursor cursor = db.fetchRoutines();

你不能调用它，因为它还没有调用onCreate()。db.fetchRoutines();将从您的数据库中调用某些内容。但是您已经创建了 db 对象。'this' 不能使用，因为该对象尚未构造。

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();
    }

这种方法

db = new DatabaseHandler(this);

是您创建对象的地方。

 db.getWritableDatabase();

是您获取数据库的地方，您只能在此行之后使用数据库操作。

于 2012-12-24T02:57:33.583 回答
1

在DatabaseHandler中，您永远不会分配 的值db。因此，当您调用db.query()时fetchRoutines()，它会崩溃。

您需要设置您的db成员变量，以便您以后可以使用它。将以下行添加到 的末尾DatabaseHandler.onCreate()：

this.db = db;
于 2012-12-24T03:18:03.323 回答