ShutterButton.java

/** 
 ** Copyright (c) 2010 Ushahidi Inc
 ** All rights reserved
 ** Contact: team@ushahidi.com
 ** Website: http://www.ushahidi.com
 ** 
 ** GNU Lesser General Public License Usage
 ** This file may be used under the terms of the GNU Lesser
 ** General Public License version 3 as published by the Free Software
 ** Foundation and appearing in the file LICENSE.LGPL included in the
 ** packaging of this file. Please review the following information to
 ** ensure the GNU Lesser General Public License version 3 requirements
 ** will be met: http://www.gnu.org/licenses/lgpl.html.	
 **	
 **
 ** If you have questions regarding the use of this file, please contact
 ** Ushahidi developers at team@ushahidi.com.
 ** 
 **/

package com.ushahidi.android.app;

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ImageView;

/**
 * A button designed to be used for the on-screen shutter button. It's currently
 * an {@code ImageView} that can call a delegate when the pressed state changes.
 */
public class ShutterButton extends ImageView {
    /**
     * A callback to be invoked when a ShutterButton's pressed state changes.
     */
    public interface OnShutterButtonListener {
        /**
         * Called when a ShutterButton has been pressed.
         * 
         * @param b The ShutterButton that was pressed.
         */
        void onShutterButtonFocus(ShutterButton b, boolean pressed);

        void onShutterButtonClick(ShutterButton b);
    }

    private OnShutterButtonListener mListener;

    private boolean mOldPressed;

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

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

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

    public void setOnShutterButtonListener(OnShutterButtonListener listener) {
        mListener = listener;
    }

    /**
     * Hook into the drawable state changing to get changes to isPressed -- the
     * onPressed listener doesn't always get called when the pressed state
     * changes.
     */
    @Override
    protected void drawableStateChanged() {
        super.drawableStateChanged();
        final boolean pressed = isPressed();
        if (pressed != mOldPressed) {
            if (!pressed) {
                // When pressing the physical camera button the sequence of
                // events is:
                // focus pressed, optional camera pressed, focus released.
                // We want to emulate this sequence of events with the shutter
                // button. When clicking using a trackball button, the view
                // system changes the the drawable state before posting click
                // notification, so the sequence of events is:
                // pressed(true), optional click, pressed(false)
                // When clicking using touch events, the view system changes the
                // drawable state after posting click notification, so the
                // sequence of events is:
                // pressed(true), pressed(false), optional click
                // Since we're emulating the physical camera button, we want to
                // have the same order of events. So we want the optional click
                // callback to be delivered before the pressed(false) callback.
                //
                // To do this, we delay the posting of the pressed(false) event
                // slightly by pushing it on the event queue. This moves it
                // after the optional click notification, so our client always
                // sees events in this sequence:
                // pressed(true), optional click, pressed(false)
                post(new Runnable() {
                    public void run() {
                        callShutterButtonFocus(pressed);
                    }
                });
            } else {
                callShutterButtonFocus(pressed);
            }
            mOldPressed = pressed;
        }
    }

    private void callShutterButtonFocus(boolean pressed) {
        if (mListener != null) {
            mListener.onShutterButtonFocus(this, pressed);
        }
    }

    @Override
    public boolean performClick() {
        boolean result = super.performClick();
        if (mListener != null) {
            mListener.onShutterButtonClick(this);
        }
        return result;
    }
}