Question

我有一个自定义ListView适配器。在ListView中，我设置了一个删除按钮。

现在我想通过点击该列表的按钮删除固定列表项。我已经能够从ListView中删除它。但是当我刷新布局活动时，列表显示在同一个地方。

也许它没有从数据库中删除。我在主要活动中创建了数据库。但是我从ListView适配器活动中删除了列表项。

这是我的ListView适配器：

import static com.example.shubho.digitalattendancesheet.Constant.FIRST_COLUMN;
import static com.example.shubho.digitalattendancesheet.Constant.SECOND_COLUMN;

public class ListViewAdapter extends BaseAdapter
{
public ArrayList<HashMap> list;
Activity activity;


public ListViewAdapter(Activity activity, ArrayList<HashMap> list) {
    super();
    this.activity = activity;
    this.list = list;
}

@Override
public int getCount() {
    // TODO Auto-generated method stub
    return list.size();
}

@Override
public Object getItem(int position) {
    // TODO Auto-generated method stub
    return list.get(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return 0;
}

private class ViewHolder {
    TextView txtFirst;
    TextView txtSecond;
}

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    // TODO Auto-generated method stub

    // TODO Auto-generated method stub
    final ViewHolder holder;
    LayoutInflater inflater =  activity.getLayoutInflater();


    if (convertView == null)
    {
        convertView = inflater.inflate(R.layout.course_display_row, null);
        holder = new ViewHolder();
        holder.txtFirst = (TextView) convertView.findViewById(R.id.t_code);
        holder.txtSecond = (TextView) convertView.findViewById(R.id.t_title);
        ImageButton delete = (ImageButton) convertView.findViewById(R.id.t_delete);

        convertView.setTag(holder);
        delete.setOnClickListener( new View.OnClickListener() {
                                    @Override
                                    public void onClick(View v) {
                                        list.remove(position);
                                        notifyDataSetChanged();



                                    }
                                }
        );
    }
    else
    {
        holder = (ViewHolder) convertView.getTag();
    }

    HashMap map = list.get(position);
    holder.txtFirst.setText((CharSequence) map.get(FIRST_COLUMN));
    holder.txtSecond.setText((CharSequence) map.get(SECOND_COLUMN));

    return convertView;
}

}

在我使用的AddCourseActivity（主要活动）中：

public class AddCourseActivity extends AppCompatActivity implements View.OnClickListener{

EditText editCourseCode,editCourseTitle;
Button btnAdd,btnEdit,btnSearch,btnShowAll;
ImageButton btnDelete;

SQLiteDatabase db;
ListView listview;
int i;

ArrayList<String> ar =null;
ArrayList<String> ar1 =null;
ArrayList<String> SampleArrayList = new ArrayList<>();

private ArrayList<HashMap> list;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_add_course);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayShowTitleEnabled(false);


    editCourseCode = (EditText)findViewById(R.id.courseCode);
    editCourseTitle = (EditText)findViewById(R.id.courseTitle);
    btnAdd = (Button)findViewById(R.id.add);
    btnShowAll = (Button)findViewById(R.id.show);
    btnEdit = (Button)findViewById(R.id.update);


    db = openOrCreateDatabase("CourseDB", Context.MODE_PRIVATE,null);
    db.execSQL("CREATE TABLE IF NOT EXISTS course(courseCode VARCHAR, courseTitle VARCHAR)");


    btnAdd.setOnClickListener(this);
    btnEdit.setOnClickListener(this);
    btnShowAll.setOnClickListener(this);
}
public void onClick(View view){
    if (view == btnAdd){
        String str = editCourseCode.getText().toString().trim();
        String str1 = editCourseTitle.getText().toString().trim();
        if(str.length()>0 && str1.length()>0){
            db.execSQL("insert into course values('" + str + "','" + str1 + "')");
            Snackbar.make(view, "Inserted", Snackbar.LENGTH_SHORT).show();
            editCourseCode.setText("");
            editCourseTitle.setText("");
        } else {
            Snackbar.make(view, "Not Inserted", Snackbar.LENGTH_SHORT).show();
        }
    }
    else if(view == btnShowAll){
        try {

            final ListView lview = (ListView) findViewById(R.id.list);
            populateList();
            final ListViewAdapter adapter = new ListViewAdapter(this, list);
            lview.setAdapter(adapter);


        } catch (Exception e) {
            Snackbar.make(view, "No record found", Snackbar.LENGTH_SHORT).show();
        }
    }
    else if(view==btnEdit){
        if(editCourseCode.getText().toString().trim().length()==0 && editCourseTitle.getText().toString().trim().length()==0){
            Snackbar.make(view, "Not Updated", Snackbar.LENGTH_SHORT).show();
            return;
        }
        else {
            if (editCourseCode.getText().toString().trim().length() != 0) {
                db.execSQL("UPDATE course set courseTitle='"+editCourseTitle.getText()+"' WHERE " + " courseCode ='"+editCourseCode.getText()+"'");
            }
            else if (editCourseTitle.getText().toString().trim().length() != 0) {
                db.execSQL("UPDATE course set courseCode='"+editCourseCode.getText()+"' WHERE " + " courseTitle ='"+editCourseTitle.getText()+"'");
            }
            Snackbar.make(view, "Updated", Snackbar.LENGTH_SHORT).show();
        }
    }
}
private void populateList() {
    // TODO Auto-generated method stub

    ar = new ArrayList();
    ar1 = new ArrayList();
    Cursor c = db.rawQuery("Select * from course", null);
    c.moveToFirst();

    do {
        ar.add(c.getString(c.getColumnIndex("courseCode")));
        ar1.add(c.getString(c.getColumnIndex("courseTitle")));
    } while (c.moveToNext());


    list = new ArrayList<HashMap>();
    for ( i = 0; i < ar.size(); i++) {

        HashMap temp = new HashMap();
        temp.put(FIRST_COLUMN, ar.get(i));
        temp.put(SECOND_COLUMN, ar1.get(i));
        list.add(temp);
    }

}







@Override
public boolean onCreateOptionsMenu(Menu menu) {

    getMenuInflater().inflate(R.menu.menu_add_course, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle item selection
    switch (item.getItemId()) {
        case R.id.action_profile:
            onBackPressed();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}




}

如何从数据库中删除固定列表项？

Answer 1

在OnClick中删除按钮，创建工作线程并执行数据库查询以删除该项。您需要唯一地标识列表中的项目，所以基本上您需要在项目上使用某种ID（我认为您已经拥有）

您可以使用AsyncTask，Handlers或Threads来执行此操作。不要在主线程上执行数据库查询，否则你的应用程序会滞后。

旁注。停止使用notifyDataSetChanged，而是使用notifyItemRemoved。

Answer 2

当您从列表中删除时，您还必须在数据库表中运行删除查询。所以onClickListener应该是这样的。

ImageButton delete = (ImageButton) convertView.findViewById(R.id.t_delete);
convertView.setTag(holder);
delete.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        // Delete from database as well
        db.rawQuery("delete from course where courseCode = '" + list.get(position).get(FIRST_COLUMN) + "'", null);

        // Now delete from list and update your ListView
        list.remove(position);
        notifyDataSetChanged();
    }
});

<强>更新

根据问题的更新。我修改了你的适配器并在其中引入了一些新的变量。请检查适配器并导入此适配器中所需的包。然后修改启动适配器的位置。

public class ListViewAdapter extends BaseAdapter {
    private ArrayList<HashMap> list;
    private Context context;
    private SQLiteDatabase db;

    public ListViewAdapter(Context context, ArrayList<HashMap> list) {
        super();
        this.context = context;
        this.list = list;
    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    private class ViewHolder {
        TextView txtFirst;
        TextView txtSecond;
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        final ViewHolder holder;

        if (convertView == null) {
            convertView = LayoutInflater.from(parent.getContext()).inflate(R.layout.course_display_row, null);
            holder = new ViewHolder();
            holder.txtFirst = (TextView) convertView.findViewById(R.id.t_code);
            holder.txtSecond = (TextView) convertView.findViewById(R.id.t_title);
            ImageButton delete = (ImageButton) convertView.findViewById(R.id.t_delete);

            convertView.setTag(holder);
            delete.setOnClickListener
                    (new View.OnClickListener() {
                         @Override
                         public void onClick(View v) {
                             db = context.openOrCreateDatabase("CourseDB", Activity.MODE_PRIVATE, null);
                             db.execSQL("DELETE from course where courseCode = '" + list.get(position).get(FIRST_COLUMN) + "'");
                             db.close();

                             list.remove(position);
                             notifyDataSetChanged();
                         }
                     }
                    );
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        HashMap map = list.get(position);
        holder.txtFirst.setText((CharSequence) map.get(FIRST_COLUMN));
        holder.txtSecond.setText((CharSequence) map.get(SECOND_COLUMN));

        return convertView;
    }
}

希望有所帮助！

Answer 3

在适配器类中创建Interface

interface OnDeleteListener {
    onDeleteCourse(String code, int position)
}

将此构造函数添加到适配器类

private OnDeleteListenre mListener;    

public ListViewAdapter(List<HashMap> items, OnDeleteListener listener) {
    mListener = listener
    ...
}

在适配器类

中添加此方法

public void refresh(int position) {
    // remove the item from the list
    list.remove(position)
    // refresh listview
    notifyDataSetChanged();
}

更改delete按钮实现，如下所示

delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // get the course code from the list according to position
                ...
                ...
                // pass this code and item position here
                mListener.onDelete(## PASS COURSE CODE HERE ##, position);
            }
        });

让Activity班级implement OnDeleteListener和

 @Override
public void onDeleteCourse(String code, int postion) {
   // Delete the course from the database here
   ...
   ... 
   // notify the adapter 
   adapter.refresh(position)
}

初始化适配器

adapter = ListViewAdapter(list, this)

列表项从ListView中删除，但不从数据库中删除

3 个答案: