Question

我有一个按下按钮时触发的功能。这是我的ScanDetailActivity课程：

Scan scan;
ScanDataSource datasource;

public void doDelete(View v) {
    Log.i(LOGTAG, "delete clicked");
    datasource.open();
    Log.i(LOGTAG, "going to delete");
    if (datasource.removeFromMyScans(scan)) {
        Log.i(LOGTAG, "Item Deleted");
        setResult(-1);
        finish();
    } else {
        Log.i(LOGTAG, "item not deleted");
    }
}

这适用于if语句。我在函数本身有一些日志信息，这是在我的 ScanDataSource.java档案：

public boolean removeFromMyScans(Scan scan) {
    Log.i(LOGTAG, "removeFromMyScans started");
    String where = ScanDBOpenHelper.COLUMN_BID + "=" + scan.getId();
    int result = database.delete(ScanDBOpenHelper.TABLE_BUYS, where, null);
    return (result == 1);
}

我从未得到“removeFromMyScans started”信息。我查看了有关删除/删除行的其他帖子，我甚至没有达到这一点。我的所有错误消息都表明它在if (datasource.removeFromMyScans(scan)行失败了。我是Android开发的新手，无法弄清楚我哪里出错了。我一直在学习Linda.com视频。

编辑

如果有帮助，以下是错误消息：

I/DATABASE(1985): Table has been created
I/DATABASE(1985): Table buys has column isbn
I/DATABASE(1985): Database opened scans
I/DATABASE(1985): Returned 0 rows in findAll
I/DATABASE(1985): Returned 32160 rows in findAll
I/DATABASE(1985): Database opened scans
I/DATABASE(1985): Returned 1 rows
I/DATABASE(1985): Scan added
I/DATABASE(1985): Returned 1 rows
I/DATABASE(1985): writeToParcel
I/DATABASE(1985): Database closed
I/DATABASE(1985): createFromParcel
I/DATABASE(1985): Parcel constructor
I/DATABASE(1985): delete clicked
D/AndroidRuntime(1985): Shutting down VM
W/dalvikvm(1985): threadid=1: thread exiting with uncaught exception (group=0xb0d3fb20)
E/AndroidRuntime(1985): FATAL EXCEPTION: main
E/AndroidRuntime(1985): Process: com.bookcellaronline.bookscanning, PID: 1985
E/AndroidRuntime(1985): java.lang.IllegalStateException: Could not execute method of the activity
E/AndroidRuntime(1985):     at android.view.View$1.onClick(View.java:3823)
E/AndroidRuntime(1985):     at android.view.View.performClick(View.java:4438)
E/AndroidRuntime(1985):     at android.view.View$PerformClick.run(View.java:18422)
E/AndroidRuntime(1985):     at android.os.Handler.handleCallback(Handler.java:733)
E/AndroidRuntime(1985):     at android.os.Handler.dispatchMessage(Handler.java:95)
E/AndroidRuntime(1985):     at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime(1985):     at android.app.ActivityThread.main(ActivityThread.java:5017)
E/AndroidRuntime(1985):     at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(1985):     at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime(1985):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
E/AndroidRuntime(1985):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
E/AndroidRuntime(1985):     at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(1985): Caused by: java.lang.reflect.InvocationTargetException
E/AndroidRuntime(1985):     at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(1985):     at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime(1985):     at android.view.View$1.onClick(View.java:3818)
E/AndroidRuntime(1985):     ... 11 more
E/AndroidRuntime(1985): Caused by: java.lang.NullPointerException
E/AndroidRuntime(1985):     at com.bookcellaronline.bookscanning.ScanDetailActivity.doDelete(ScanDetailActivity.java:62)
E/AndroidRuntime(1985):     ... 14 more
I/DATABASE(2027): Database opened scans
I/DATABASE(2027): Returned 32160 rows in findAll
I/DATABASE(2027): Database opened scans

ScanDataSource类：

public class ScanDataSource {

    public static final String LOGTAG = "DATABASE";

    SQLiteOpenHelper dbhelper;
    SQLiteDatabase database;

    private static final String[] allColumns = {
            ScanDBOpenHelper.COLUMN_ID, ScanDBOpenHelper.COLUMN_ISBN, ScanDBOpenHelper.COLUMN_TITLE,
            ScanDBOpenHelper.COLUMN_AUTHOR, ScanDBOpenHelper.COLUMN_PRICE, ScanDBOpenHelper.COLUMN_IE,
            ScanDBOpenHelper.COLUMN_LIMIT, ScanDBOpenHelper.COLUMN_NOTE, ScanDBOpenHelper.COLUMN_RANK,
            ScanDBOpenHelper.COLUMN_SUPPLY, ScanDBOpenHelper.COLUMN_BILLING
    };

    public ScanDataSource(Context context) {
        dbhelper = new ScanDBOpenHelper(context);
    }

    public void open() {
        database = dbhelper.getWritableDatabase();
        Log.i(LOGTAG, "Database opened scans");
    }

    public void close() {
        Log.i(LOGTAG, "Database closed");
        dbhelper.close();
    }

    private List<Scan> cursorToScanned(Cursor cursor) {
        List<Scan> scans = new ArrayList<Scan>();
        if (cursor.getCount() > 0) {
            while (cursor.moveToNext()) {
                Scan scan = new Scan();
                scan.setId(cursor.getLong(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_BID)));
                scan.setIsbn(cursor.getString(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_BISBN)));
                scan.setQuantity(cursor.getString(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_QUANTITY)));
                scan.setPrice(cursor.getDouble(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_BPRICE)));
                scan.setTitle(cursor.getString(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_TITLE)));
                scan.setAuthor(cursor.getString(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_AUTHOR)));
                scan.setIePrice(cursor.getDouble(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_IE)));
                scan.setMaxLimit(cursor.getString(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_LIMIT)));
                scan.setSupply(cursor.getString(cursor.getColumnIndex(ScanDBOpenHelper.COLUMN_SUPPLY)));
                scans.add(scan);
            }
        }
        return scans;
    }

    public boolean addToMyScans(Scan scan) {
        ContentValues values = new ContentValues();
        values.put(ScanDBOpenHelper.COLUMN_BISBN, scan.getIsbn());
        values.put(ScanDBOpenHelper.COLUMN_QUANTITY, "1");
        values.put(ScanDBOpenHelper.COLUMN_BPRICE, scan.getPrice());
        long result = database.insert(ScanDBOpenHelper.TABLE_BUYS, null, values);
        scan.setId(result);
        return (result != -1);
    }

    public boolean removeFromMyScans(Scan scan) {
        Log.i(LOGTAG, "removeFromMyScans started");
        String where = ScanDBOpenHelper.COLUMN_BID + "=" + scan.getId();
        int result = database.delete(ScanDBOpenHelper.TABLE_BUYS, where, null);
        return (result == 1);
    }

    public boolean updateMyScans(Scan scan) {
        Log.i(LOGTAG, "update started");
        ContentValues values = new ContentValues();
        values.put(ScanDBOpenHelper.COLUMN_BPRICE, scan.getPrice());
        values.put(ScanDBOpenHelper.COLUMN_QUANTITY, scan.getQuantity());
        String where = ScanDBOpenHelper.COLUMN_BID + "=" + scan.getId();
        int result = database.update(ScanDBOpenHelper.TABLE_BUYS, values, where, null);
        return (result == 1);
    }

    public List<Scan> findMyScans() {
        String query = "SELECT buys_id,quantity, buyer_temp.price, scan_final.* "
                + " FROM buyer_temp inner join scan_final on scan_final.isbn = buyer_temp.isbn";
        Cursor cursor = database.rawQuery(query, null);

        Log.i(LOGTAG, "Returned " + cursor.getCount() + " rows");

        List<Scan> scans = cursorToScanned(cursor);
        return scans;
    }
}

Answer 1

根据日志和您的评论，例外的原因是datasource方法null为doDelete。在代码中搜索您初始化datasource字段的位置以及将其设置为null的位置。您可能会在onCreate方法中对其进行初始化，但在null或onPause中设置为onStop。（这不起作用，因为在活动停止后没有再次调用onCreate但是没有销毁。请查看Activity lifecycle以获取详细信息。）

调用函数删除行

1 个答案: