从recyclerview项目中将选定的RadioButton文本保存在模型类中

Question

From RecyclerView item, I am trying to save the selected RadioButton's text in model class. When I select a RadioButton from 1st item, it's text is saved appropriately. Problem is, RadioButton's text at the same position from 8th item is also auto saved. If I select radio button from 2nd item, text from 9th item is also auto saved, and so on. How to solve this problem?

onBindViewHolder method is given below :

    @Override
    public void onBindViewHolder(@NonNull final ViewHolder holder, final int position) {

    ...

    holder.radioGroup.setTag(position);
    holder.radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {

            int radioButtonID = group.getCheckedRadioButtonId();
            RadioButton radioButton = (RadioButton) group.findViewById(radioButtonID);
            int clickedPos = (Integer) group.getTag();
            models.get(clickedPos).setChecked(radioButtonID);

            if (radioButtonID > 0){
                models.get(clickedPos).setSelectedAns(radioButton.getText().toString());
            }

        }
    });
    holder.radioGroup.check(models.get(position).getChecked());
    Log.d("TAG", "At position " + position + " selected : " + models.get(position).getSelectedAns());

}

Answer 1

The problem is that although the code looks correct on the surface, what's actually happening is that when you call holder.radioGroup.check() , it triggers your onCheckedChanged() event handler just the same as if the user had initiated it.

Since the views are recycled, the view at position 0 is being reused for position 8 in the list. So the call to check() in onBindViewHolder() will call onCheckedChanged() , with the checked radio button from position 0 still checked (ie checkedId and radioGroup. getCheckedRadioButtonId() will return the ID of the radiobutton checked when the view was used at position 0).

The real crux is this

models.get(clickedPos).setChecked(radioButtonID);

Consider the first paragraphs of the answer, and you'll realize that this will (incorrectly) update the model item at position 8 with the radioButtonID that was checked when this view was used at position 0.

One way to solve this is to distinguish between a user-initiated change and a binding-initiated change. You can for example do this by adding a field to the ViewHolder to indicate if the view is currently binding.

class ViewHolder extends RecyclerView.ViewHolder{
    TextView selectedAnswer;
    RadioGroup radioGroup;

    boolean isBinding;

    ViewHolder(View itemView) {
        super(itemView);

        radioGroup = itemView.findViewById(R.id.radioGroup);

        radioGroup.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {
                int position = getAdapterPosition();

                RadioButton radioButton = (RadioButton) group.findViewById(checkedId);

                /* Only update the model when onCheckedChange() was initiated by the user clicking
                   a radio button, not when the adapter is binding the view. In that scenario, we
                   are only interested in passing information FROM the model TO the view. */
                if( !isBinding ) {
                    models.get(position).setChecked(checkedId);
                    models.get(position).setSelectedAns(radioButton != null ? radioButton.getText().toString() : "");
                }

                selectedAnswer.setText(  models.get(position).getSelectedAns() );
            }
        });

        ...
    }
}

@Override
public void onBindViewHolder(@NonNull final ViewHolder holder, final int position) {
    holder.isBinding = true;

    ...

    /* When calling check() here, we invoke onCheckedChanged(), which will
       update the textview that displays the selected answer - so no need to call
           holder.selectedAnswer.setText(  models.get(position).getSelectedAns() )
       from here */
    holder.radioGroup.check(models.get(position).getChecked());

    holder.isBinding = false;
}