Spinner - focus to first item

问题:

I use dropdown spinner with cursor adapter. It contains e.g 1 - 100 items. I select e.g. item 50. Item is selected. Next time when I open spinner first visible row is item 50. How can I achieve that when I open spinner it will focus to first item/first visible item will be item 1?

I mean like autoscroll up in the list, so first visible item in dropdown is 1st one and not selected one.

回答1:

You can make the Spinner do what you want by extending it and overriding the two methods that are responsible for setup/showing the list of values:

public class CustomSpinnerSelection extends Spinner {

    private boolean mToggleFlag = true;

    public CustomSpinnerSelection(Context context, AttributeSet attrs,
            int defStyle, int mode) {
        super(context, attrs, defStyle, mode);
    }

    public CustomSpinnerSelection(Context context, AttributeSet attrs,
            int defStyle) {
        super(context, attrs, defStyle);
    }

    public CustomSpinnerSelection(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomSpinnerSelection(Context context, int mode) {
        super(context, mode);
    }

    public CustomSpinnerSelection(Context context) {
        super(context);
    }

    @Override
    public int getSelectedItemPosition() {
        // this toggle is required because this method will get called in other
        // places too, the most important being called for the
        // OnItemSelectedListener
        if (!mToggleFlag) {
            return 0; // get us to the first element
        }
        return super.getSelectedItemPosition();
    }

    @Override
    public boolean performClick() {
        // this method shows the list of elements from which to select one.
        // we have to make the getSelectedItemPosition to return 0 so you can
        // fool the Spinner and let it think that the selected item is the first
        // element
        mToggleFlag = false;
        boolean result = super.performClick();
        mToggleFlag = true;
        return result;
    }

}

It should work just fine for what you want to do.

回答2:

You can set the selection of a Spinner to the first item like this:

yourspinner.setSelection(0);

You might want to do this in the onStart() method.

回答3:

This short of code will do the work for you.

    int prevSelection=0;
    spSunFrom = (Spinner) findViewById(R.id.spTimeFromSun);
    spSunFrom.setOnTouchListener(new OnTouchListener() {

        public boolean onTouch(View v, MotionEvent event) {
            // TODO Auto-generated method stub
            prevSelection = spSunFrom.getSelectedItemPosition();
            spSunFrom.setSelection(0);
            return false;
        }
    });
    spSunFrom.setOnItemSelectedListener(new OnItemSelectedListener() {

        @Override
        public void onItemSelected(AdapterView<?> arg0, View arg1,
                int arg2, long arg3) {
            if(arg2==0)
                spSunFrom.setSelection(prevSelection);
            prevSelection = arg2;

        }

        @Override
        public void onNothingSelected(AdapterView<?> arg0) {
            spSunFrom.setSelection(prevSelection);
        }
    });