我正在创建一个在片段中显示 ListView 的演示 Android 应用程序。每个 List 项都有一个文本和一个删除按钮，这些项存储在 SQLite 数据库中。单击删除按钮时，我无法理解如何从数据库中删除相应的项目。网上找了各种方法，一直想不通如何获取DB中row item的_ID值（设置为autoincrement），以便删除该item。
自定义适配器类
public class CustomListAdapter extends ArrayAdapter<DataModel> implements View.OnClickListener{
private ArrayList<DataModel> dataSet;
Context mContext;
private TaskHelper_tab1 mHelper;
public CustomListAdapter(@NonNull Context context, int resource, @NonNull ArrayList<DataModel> data) {
super(context, resource, data);
this.dataSet = data;
this.mContext=context;
}
private static class ViewHolder {
TextView txtName;
Button btn;
}
@Override
public void onClick(View v) {
int position=(Integer) v.getTag();
Object object= getItem(position);
DataModel dataModel=(DataModel)object;
switch (v.getId())
{
case R.id.task_delete:
Snackbar.make(v, "Release date " +dataModel.getName(), Snackbar.LENGTH_LONG)
.setAction("No action", null).show();
break;
}
}
private int lastPosition = -1;
@SuppressLint("NewApi")
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
// Get the data item for this position
final DataModel dataModel = getItem(position);
// Check if an existing view is being reused, otherwise inflate the view
final ViewHolder viewHolder; // view lookup cache stored in tag
final View result;
if (convertView == null) {
viewHolder = new ViewHolder();
LayoutInflater inflater = LayoutInflater.from(getContext());
convertView = inflater.inflate(R.layout.task_list_long_term_item, parent, false);
viewHolder.txtName = (TextView) convertView.findViewById(R.id.task_title);
viewHolder.btn = (Button) convertView.findViewById(R.id.task_delete);
result=convertView;
convertView.setTag(viewHolder);
viewHolder.btn.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
int id2 = (int) getItemId(position);
Toast.makeText(mContext,id2 + " Button clicked" + position,Toast.LENGTH_SHORT).show();
deleteTask(id2);
notifyDataSetChanged();
}
});
} else {
viewHolder = (ViewHolder) convertView.getTag();
result=convertView;
}
lastPosition = position;
viewHolder.txtName.setText(dataModel.getName());
return convertView;
}
public void deleteTask(int position){
mHelper = new TaskHelper_tab1(getContext());
SQLiteDatabase db = mHelper.getWritableDatabase();
db.execSQL("DELETE FROM " + Task_tab1.TaskEntry.TABLE + " WHERE " + Task_tab1.TaskEntry._ID + "= '" + position + "'");
db.close();
}
}
片段代码
public class fragment_tab1 extends Fragment{
//for db tasks
EditText editText = null;
private TaskHelper_tab1 mHelper;
FloatingActionButton fab_tab1;
private PopDialog.PopDialogListener listener; //listener to pass the text to parent activity
private TextView textViewDescr;
private CustomListAdapter mAdapter;
private View view;
private ListView list_calllog;
private ArrayList<DataModel> callLog;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
mHelper = new TaskHelper_tab1(getContext());
list_calllog = (ListView) getActivity().findViewById(R.id.list);
updateUI(); //this works -- keep this to initially populate the UI on opening app
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
if(view==null)
{
view=inflater.inflate(R.layout.fragment_tab1, container,false);
}
else
{
ViewGroup parent = (ViewGroup) view.getParent();
parent.removeView(view);
}
callLog= new ArrayList<>();
callLog.add(new DataModel("Apple Pie", null)); //maybe add button here
callLog.add(new DataModel("Banana Bread",null ));
CustomListAdapter adapter=new CustomListAdapter(getActivity(),R.layout.task_list_long_term_item,callLog);
list_calllog=(ListView)view.findViewById(R.id.list);
list_calllog.setAdapter(adapter);
fab_tab1 = (FloatingActionButton) view.findViewById(R.id.fab_tab1);
fab_tab1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View tab1) {
AlertDialog.Builder alert = new AlertDialog.Builder(getContext());
LayoutInflater inflater = getActivity().getLayoutInflater();
View view = inflater.inflate(R.layout.pop_dialog_layout, null);
alert.setTitle("info")
.setMessage("dialog box message")
.setView(view)
.setPositiveButton("ok", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
String edittext_descr = editText.getText().toString();
applyTexts(edittext_descr);
Toast toast = Toast.makeText(getContext(), "adadadaa", Toast.LENGTH_LONG);
toast.setGravity(Gravity.CENTER_VERTICAL, 0, 0);
toast.show();
}
}
);
alert.show();
editText = view.findViewById(R.id.edit_text);
}
});
return view;
}
@Override
public void applyTexts(String edittext_descr) {
String task = String.valueOf(edittext_descr);
SQLiteDatabase db = mHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(Task_tab1.TaskEntry.COL_TASK_TITLE, task);
db.insertWithOnConflict(Task_tab1.TaskEntry.TABLE, null, values, SQLiteDatabase.CONFLICT_REPLACE);
db.close();
updateUI();
}
private void updateUI() {
ArrayList<DataModel> taskList = new ArrayList<>();
SQLiteDatabase db = mHelper.getReadableDatabase();
Cursor cursor = db.query(Task_tab1.TaskEntry.TABLE,
new String[] {Task_tab1.TaskEntry._ID, Task_tab1.TaskEntry.COL_TASK_TITLE}, null, null, null, null, null);
while(cursor.moveToNext()){
int index = cursor.getColumnIndex(Task_tab1.TaskEntry.COL_TASK_TITLE);
//add new task
String str = cursor.getString(index);
DataModel dm = new DataModel(str,null );
taskList.add(dm);
}
if(mAdapter == null){
mAdapter = new CustomListAdapter(getActivity(), R.layout.task_list_long_term_item, taskList );
list_calllog.setAdapter(mAdapter);
} else {
mAdapter.clear();
mAdapter.addAll(taskList);
mAdapter.notifyDataSetChanged();
}
cursor.close();
db.close();
}
}