Question

所以，我试着编写一个程序，我可以创建任务，在listview中显示他们的名字和日期，只需在listview中单击它们后编辑它们

我在填充方面遇到了一些问题。我需要将SimpleCursorAdapter用于此程序（作为我大学的作业）

这是我的填充函数，它位于我的MainActivity

中

 private void populate(){
    Cursor cursor = myDb.getAllRows();
    String[] backDB = new String[] {DBAdapter.COLUMN_NAME, DBAdapter.COLUMN_DATE};
    int[] toView = new int[] {R.id.textViewName, R.id.textViewDate};
    SimpleCursorAdapter myCursor;
    myCursor = new SimpleCursorAdapter(getBaseContext(), R.layout.row_layout, cursor, backDB,toView, 0);
    ListView myList = (ListView) findViewById(R.id.listViewTasks);
    myList.setAdapter(myCursor);
}

我在想它可能与sql数据库有关，尤其是getAllRows函数，因为在logcat中我可以看到该行存在问题：

 myCursor = new SimpleCursorAdapter(getBaseContext(), R.layout.row_layout, cursor, backDB,toView, 0);

所以，这是我的getAllRows函数

 public Cursor getAllRows() {
    String query = "SELECT * FROM " + TABLE_NAME;
    Cursor c = db.rawQuery(query, null);
    c.moveToFirst();
    return c;
}

我的程序崩溃并且一直崩溃。

Answer 1

猜测您的问题是由于您没有名为 _id 的列，在这种情况下，日志将包含以下内容： -

06-07 10:53:53.957 1178-1178/so50635292.so50635292 E/AndroidRuntime: FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{so50635292.so50635292/so50635292.so50635292.MainActivity}: java.lang.IllegalArgumentException: column '_id' does not exist
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
        at android.app.ActivityThread.access$600(ActivityThread.java:130)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4745)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.IllegalArgumentException: column '_id' does not exist
        at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:302)
        at android.widget.CursorAdapter.init(CursorAdapter.java:168)
        at android.widget.CursorAdapter.<init>(CursorAdapter.java:145)
        at android.widget.ResourceCursorAdapter.<init>(ResourceCursorAdapter.java:91)
        at android.widget.SimpleCursorAdapter.<init>(SimpleCursorAdapter.java:104)
        at so50635292.so50635292.MainActivity.populate(MainActivity.java:31)
        at so50635292.so50635292.MainActivity.onCreate(MainActivity.java:23)
        at android.app.Activity.performCreate(Activity.java:5008)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
        at android.app.ActivityThread.access$600(ActivityThread.java:130) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:137) 
        at android.app.ActivityThread.main(ActivityThread.java:4745) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:511) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
        at dalvik.system.NativeStart.main(Native Method)

相关部分为 java.lang.IllegalArgumentException: column '_id' does not exist

游标适配器需要此列，它也应该是rowid的别名。该行的别名是一个定义为?? INTEGER PRIMARY KEY的列，可选的后续AUTOINCREMENT关键字也可以编码。但是，通常它不应该因为编码AUTO INCREMENT而存在开销。

要解决此问题，您可以将列添加到表中，在DBAdapter的onCreate方法中创建sql，然后删除App的数据或卸载App，然后重新运行App。

您也可以通过更改

查询数据时创建别名

 String query = "SELECT * FROM " + TABLE_NAME;

到

String query = "SELECT rowid AS _id,* FROM " + TABLE_NAME;

请注意，以下假设您尚未编写WITHOUT ROWID

使用SimpleCursorAdapter从SQL DB填充ListView时出错

1 个答案: