android - 列表项从 ListView 中删除，但不从数据库中删除

标签 android mysql database listview

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

enter image description here

现在我想通过单击该列表的按钮来删除固定列表项。我已经能够从 ListView 中删除它。但是当我刷新布局 Activity 时，列表显示在同一位置。

也许它没有从数据库中删除。我在主要 Activity 中创建了数据库。但我从 ListView 适配器 Activity 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;
}

}

在我的 AddCourseActivity(主要 Activity )中，我使用了:

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？

最佳答案

当您从列表中删除时，您只需在数据库表中运行删除查询即可。所以 onClickListener 应该如下所示。 

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();
    }
});

更新

基于问题的更新。我修改了您的适配器并在其中引入了一些新变量。请检查适配器并导入该适配器中所需的包。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;
    }
}

希望有帮助!

关于android - 列表项从 ListView 中删除，但不从数据库中删除，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/49595506/

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