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我通过长按 ListView 项编写了一个带有 SQLite ADD 和 DELETE 功能的简单 APP。但是执行DELETE时有错误。

Logcat（已解决）

04-17 21:19:42.433: E/AndroidRuntime(4067): FATAL EXCEPTION: main
04-17 21:19:42.433: E/AndroidRuntime(4067): java.lang.NullPointerException
04-17 21:19:42.433: E/AndroidRuntime(4067):     at tw.danny.idcc_hw2.savedHeadlinesFragment$1.onItemLongClick(savedHeadlinesFragment.java:91)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at android.widget.AbsListView.performLongPress(AbsListView.java:2921)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at android.widget.AbsListView$CheckForLongPress.run(AbsListView.java:2871)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at android.os.Handler.handleCallback(Handler.java:615)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at android.os.Looper.loop(Looper.java:137)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at android.app.ActivityThread.main(ActivityThread.java:4745)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at java.lang.reflect.Method.invokeNative(Native Method)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at java.lang.reflect.Method.invoke(Method.java:511)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-17 21:19:42.433: E/AndroidRuntime(4067):     at dalvik.system.NativeStart.main(Native Method)

我的 APP 是使用 ListView 片段显示数据（标题）和 longClick 项目将其添加到数据库中。在activity2中，以相同的布局显示数据库中的所有数据（标题）。从现在开始，所有功能都运行良好。当我想在activity2中使用与activity1中的ADD相同的操作来实现DELETE时，问题就出现了。

onItemLongClick 监听器（用于删除的活动 2）

@Override
public void onActivityCreated(Bundle savedState) {
    super.onActivityCreated(savedState);

    getListView().setOnItemLongClickListener(new OnItemLongClickListener() {

        @Override
        public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                int position, long arg3) {

            //Long press to delete article from db
            int rnumber =  dbHlp.DELETEColumData(RSSData.Headlines.get(position));

            if(rnumber==1)
                Toast.makeText(getActivity(), "Deleted.", Toast.LENGTH_LONG).show();
            else if(rnumber==0)
                Toast.makeText(getActivity(), "Delete Error!", Toast.LENGTH_LONG).show();

            return true;
        }
    });
}

onItemLongClick 侦听器（用于添加的活动 1）

@Override
public void onActivityCreated(Bundle savedState) {
    super.onActivityCreated(savedState);

    getListView().setOnItemLongClickListener(new OnItemLongClickListener() {

        @Override
        public boolean onItemLongClick(AdapterView<?> arg0, View arg1,
                int position, long arg3) {
            //Long press to add article to db
            long rowID =  dbHlp.ADDColumData(RSSData.Headlines.get(position), RSSData.Articles.get(position));


            Toast.makeText(getActivity(), "Add to list. id:"+rowID, Toast.LENGTH_LONG).show();

            return true;
        }
    });
}

SQLiteOpenHelper 中的函数

public class RSSDBHlp extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "ReadLater";
private static final int DATABASE_VERSION = 1;
private static final String TABLE_NAME = "article";
private static final String TABLE_CREATE = 
                "CREATE TABLE " + TABLE_NAME + " ( " +
                " id integer primary key autoincrement, " +
                " title TEXT NOT NULL, " +
                " detail TEXT );";

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

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(TABLE_CREATE);
}

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


public long ADDColumData(String Title,String Detail) {
    SQLiteDatabase db = getWritableDatabase();      
    ContentValues values =new ContentValues();
    values.put("title", Title);
    values.put("detail", Detail);
    long rowID =db.insert(TABLE_NAME, null, values);

    db.close();
    return rowID;
}

public int DELETEColumData(String Title) {
    SQLiteDatabase db = getWritableDatabase();
    Log.d("MSG","DELETE:"+Title);
    String whereClause = "title='" + Title + "'";
    int rnumber = db.delete(TABLE_NAME, whereClause, null);

    //0:error 1:all row delete

    db.close();
    return rnumber;
}

有什么问题，我只在 ADD 函数上复制和修改一些代码，效果很好。

删除返回

 Returns
the number of rows affected if a whereClause is passed in, 0 otherwise. To remove all rows and get a count pass "1" as the whereClause.
4

2 回答 2

0

空指针异常

您尚未初始化变量dbHlp。所以它的投掷NullPointerException。

dbHlp在第一次使用之前进行初始化。IE，

dbHlp = new RSSDBHlp();

从 sqllite 中删除行返回 0

修改语句

String whereClause = "title='" + Title + "'";
int rnumber = db.delete(TABLE_NAME, whereClause, null);

如下

int rnumber = db.delete(TABLE_NAME, "title=?", new String[] {Title});
于 2013-04-17T13:38:50.947 回答
0

它看起来像是一个调试的东西，与在你面前的调试器相比，在没有工作的情况下查看代码有时并不容易。

我最好的猜测是，假设您 100% 确定 dbHlp 变量已被初始化，那么 RSSData.Headlines 或 RSSData 为空。我将开始朝这个方向进行调试，但是很难通过所提供的信息来提供 100% 有用的答案。

问候

于 2013-04-17T13:59:26.513 回答