从微调框删除DropDownViewResource-Java Android Studio

Question

I have a spinner that I create like this:

        operatorSpinner = new Spinner(this);
        operatorSpinnerArrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_dropdown_item, operatorSpinnerArray);
        operatorSpinnerArrayAdapter.setDropDownViewResource(R.layout.spinner_item);
        operatorSpinner.setAdapter(operatorSpinnerArrayAdapter);

The layout, spinner_item is this:

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/text1"
    android:layout_width="28dip"
    android:layout_height="28dip"
    android:gravity="center"
    android:background="@drawable/circle"
    android:textColor="#a4a3a3" />

My reason for applying this layout is to add a circle to the background of each item in the Spinner's dropdown list. However, I only want the circle background applied under certain conditions, so I need a way to programmatically remove either the DropDownViewResource or the layout background within that resource.

I tried this:

operatorSpinnerArrayAdapter.setDropDownViewResource(0);

but it resulted in the app crashing when that code executes. I found a way to achieve what I want by replacing the adapter with a new adapter like this:

operatorSpinnerArrayAdapter = new ArrayAdapter<String>(context, android.R.layout.simple_spinner_dropdown_item, operatorSpinnerArray);
                    operatorSpinner.setAdapter(operatorSpinnerArrayAdapter);

However, my 'feeling' is that creating a new adapter every time I want to change its background is not the best approach. This is my first app I'm trying to develop so I'm not experienced, but I suspect this approach may eat up resources if repeated many times. Can anybody suggest a better approach or confirm/falsify my concerns? Thanks

Answer 1

I recommend you to make a custom adapter by which you can play with whatever the customization you want.

Take a look at http://theopentutorials.com/tutorials/android/listview/android-custom-listview-with-image-and-text-using-baseadapter/

Don't extend your custom adapter to Array adapter but BaseAdapter.Yo need to pass a RowItem like

class RowItem{
     ...
     boolean isConditionSatisfied;
     ...
}

and in you adapter override the getView() as

public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder = null;

    LayoutInflater mInflater = (LayoutInflater) 
        context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
    if (convertView == null) {
        convertView = mInflater.inflate(R.layout.list_item, null);
        holder = new ViewHolder();
        holder.txtDesc = (TextView) convertView.findViewById(R.id.desc);
        holder.txtTitle = (TextView) convertView.findViewById(R.id.title);
        holder.imageView = (ImageView) convertView.findViewById(R.id.icon);
        convertView.setTag(holder);
    }
    else {
        holder = (ViewHolder) convertView.getTag();
    }

    RowItem rowItem = (RowItem) getItem(position);

    holder.txtDesc.setText(rowItem.getDesc());
    holder.txtTitle.setText(rowItem.getTitle());
    holder.imageView.setImageResource(rowItem.getImageId());

    if(isConditionSatisfied){
       convertView.setBackground(R.drawable.your_drawable);
    }

    return convertView;
}