尝试执行删除查询时出错

Question

我想在适配器 class 中单击按钮时执行 2 个查询，第一个是来自 table A 的 select 数据并插入到 Table B，另一个是从 table A.

中删除行

适配器

 mdb = new MyDatabaseHelper(v.getContext());
 database = mdb.getReadableDatabase();
 deleteTask = new DeleteTask();
 Cursor cursor = database.rawQuery("SELECT * FROM " + MyDatabaseHelper.TABLE__TASK + " WHERE ID = ? ", new String[]{id+""}, null);
 if (cursor != null && cursor.getCount() > 0) {
        while (cursor.moveToNext()) {
              String allTask = cursor.getString(cursor.getColumnIndex("Title"));
             String name = cursor.getString(cursor.getColumnIndex("Name"));
             String allTime = cursor.getString(cursor.getColumnIndex("Time"));
             String allDate = cursor.getString(cursor.getColumnIndex("Date"));
             insertDataToCompleteTab(id, name, allTask, allTime, allDate); //insert to Completed table
             deleteTask.deleteData(id); // delete the row of data from Task Table
       }
 }

删除任务

  public void deleteData(int id)
    {
        database = mdb.getWritableDatabase();
        database.delete(MyDatabaseHelper.TABLE__TASK, MyDatabaseHelper.ID1 + "=" + id,null);
        database.close();
    }

错误

java.lang.NullPointerException
            at com.example.seng.healthyapp.DeleteTask.deleteData(DeleteTask.java:124)
            at com.example.seng.healthyapp.adapter.AllAdapter.onClick(AllAdapter.java:139)
            at android.view.View.performClick(View.java:4230)

指向 deleteTask 方法的错误。但是我已经完成了初始化，为什么我仍然会出现这样的错误？

Answer 1

这是因为您在删除查询中传递了 null，请像这样更新您的代码并检查

public void deleteData(int id)
    {
        database = mdb.getWritableDatabase();
        database.delete(MyDatabaseHelper.TABLE__TASK, MyDatabaseHelper.ID1 + "=?" , new String[] {id});
        database.close();
    }

Answer 2

它对我有用，试试看...您可以更改此代码以删除所有...

db= myDb.getWritableDatabase();
db.delete(TABLE_NAME, " ID=? " , new String[] {id},null);
db.close();

Answer 3

到处搜索后，我决定删除 deleteTask = new DeleteTask(); 并只使用 deleteData(id) 而不是 deleteTask.deleteData(id);。在适配器中调用方法，但不在适配器中调用其他 class 对象。

尝试执行删除查询时出错

Get error when trying to perform delete query

sqlite

android

insert

delete-row