Spinner:如何知道项目选择是通过编程方式更改还是通过用户操作通过UI更改

Question

我有运行OnItemSelectedListenerspinner事件的代码.所以,当我在方法中时:

public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {
    // I want to do something here if it's a user who changed the the selected item
}

...我如何知道项目选择是通过编程方式完成还是通过用户操作通过UI完成？

Answer 1

我不知道这可以从方法中区分出来.实际上,这是一个很多人面临的问题,onItemSelected当启动微调器时会被解雇.目前似乎唯一的解决方法是使用外部变量.

private Boolean isUserAction = false;

...

public void onItemSelected( ... ) {

    if( isUserAction ) {
       // code for user initiated selection
    } else {
       // code for programmatic selection
       // also triggers on init (hence the default false)
    }

    // reset variable, so that it will always be true unless tampered with
    isUserAction = true;
}

public void myButtonClick( ... ) {
    isUserAction = false;
    mySpinner.setSelectedItem ( ... );
}

Answer 2

我制作了一个新的Spinner类来封装上面提到的原则.但即便如此,你必须确保调用正确的方法而不是setSelection

在要点中也是如此

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.AdapterView;

/**
 * Used this to differentiate between user selected and prorammatically selected
 * Call {@link Spinner#programmaticallySetPosition} to use this feature.
 * Created by vedant on 6/1/15.
 */
public class Spinner extends android.widget.Spinner implements AdapterView.OnItemSelectedListener {

    OnItemSelectedListener mListener;

    /**
     * used to ascertain whether the user selected an item on spinner (and not programmatically)
     */
    private boolean mUserActionOnSpinner = true;

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

        if (mListener != null) {

            mListener.onItemSelected(parent, view, position, id, mUserActionOnSpinner);
        }
        // reset variable, so that it will always be true unless tampered with
        mUserActionOnSpinner = true;
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {
        if (mListener != null)
            mListener.onNothingSelected(parent);
    }

    public interface OnItemSelectedListener {
        /**
         * <p>Callback method to be invoked when an item in this view has been
         * selected. This callback is invoked only when the newly selected
         * position is different from the previously selected position or if
         * there was no selected item.</p>
         *
         * Impelmenters can call getItemAtPosition(position) if they need to access the
         * data associated with the selected item.
         *
         * @param parent The AdapterView where the selection happened
         * @param view The view within the AdapterView that was clicked
         * @param position The position of the view in the adapter
         * @param id The row id of the item that is selected
         */
        void onItemSelected(AdapterView<?> parent, View view, int position, long id, boolean userSelected);

        /**
         * Callback method to be invoked when the selection disappears from this
         * view. The selection can disappear for instance when touch is activated
         * or when the adapter becomes empty.
         *
         * @param parent The AdapterView that now contains no selected item.
         */
        void onNothingSelected(AdapterView<?> parent);
    }

    public void programmaticallySetPosition(int pos, boolean animate) {
        mUserActionOnSpinner = false;
        setSelection(pos, animate);
    }

    public void setOnItemSelectedListener (OnItemSelectedListener listener) {
        mListener = listener;
    }

    public Spinner(Context context) {
        super(context);
        super.setOnItemSelectedListener(this);
    }

    public Spinner(Context context, int mode) {
        super(context, mode);
        super.setOnItemSelectedListener(this);
    }

    public Spinner(Context context, AttributeSet attrs) {
        super(context, attrs);
        super.setOnItemSelectedListener(this);
    }

    public Spinner(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        super.setOnItemSelectedListener(this);
    }

    public Spinner(Context context, AttributeSet attrs, int defStyle, int mode) {
        super(context, attrs, defStyle, mode);
        super.setOnItemSelectedListener(this);
    }
}

Answer 3

您可以使用Spinner的setOnTouchListener()方法相当简单地获得所需的结果：

// Instance variables
boolean spinnerTouched = false;
Spinner spinner;

// onCreate() / onCreateView() / etc. method..
spinner = ...;
spinner.setOnTouchListener(new View.OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {

        if (event.getAction() == MotionEvent.ACTION_DOWN) {
            spinnerTouched = true; // User DID touched the spinner!
        }

        return false;
    }
});
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {

        if (spinnerTouched) {
            // Do something
        }
        else {
            // Do something else
        }

    }

    @Override
    public void onNothingSelected(AdapterView<?> parentView) {
    }
});

// Your method that you use the change the spinner selection programmatically...
private void changeSpinnerSelectionProgrammatically(int pos) {
    stateSpinnerTouched = false; // User DIDN'T touch the spinner
    boolean useAnimation = false;
    spinner.setSelection(pos, useAnimation); // Calls onItemSelected()
}