CrossFadeSlidingPaneLayout.java

package net.xpece.material.navigationdrawer.list;

import android.annotation.TargetApi;
import android.content.Context;
import android.os.Build;
import android.support.v4.widget.SlidingPaneLayout;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

import com.nineoldandroids.view.ViewHelper;

/**
 * @author https://github.com/chiuki/sliding-pane-layout
 * @author http://blog.sqisland.com/2015/01/partial-slidingpanelayout.html
 */
public class CrossFadeSlidingPaneLayout extends SlidingPaneLayout {
    private View partialView = null;
    private View fullView = null;

    // helper flag pre honeycomb - visibility and click response handling
    private boolean mWasOpened = false;

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

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

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

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();

        if (getChildCount() < 1) {
            return;
        }

        View panel = getChildAt(0);
        if (!(panel instanceof ViewGroup)) {
            return;
        }

        ViewGroup viewGroup = (ViewGroup) panel;
        if (viewGroup.getChildCount() != 2) {
            return;
        }
        fullView = viewGroup.getChildAt(0);
        partialView = viewGroup.getChildAt(1);

        super.setPanelSlideListener(crossFadeListener);
    }

    @Override
    public void setPanelSlideListener(final PanelSlideListener listener) {
        if (listener == null) {
            super.setPanelSlideListener(crossFadeListener);
            return;
        }

        super.setPanelSlideListener(new PanelSlideListener() {
            @Override
            public void onPanelSlide(View panel, float slideOffset) {
                crossFadeListener.onPanelSlide(panel, slideOffset);
                listener.onPanelSlide(panel, slideOffset);
            }

            @Override
            public void onPanelOpened(View panel) {
                crossFadeListener.onPanelOpened(panel);
                listener.onPanelOpened(panel);
            }

            @Override
            public void onPanelClosed(View panel) {
                crossFadeListener.onPanelClosed(panel);
                listener.onPanelClosed(panel);
            }
        });
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);

        // this has to be done on each layout (changed means views were added or removed)
        if (partialView != null) {
            updateVisibility(isOpen());
        }
    }

    private SimplePanelSlideListener crossFadeListener = new SimplePanelSlideListener() {
        @Override
        public void onPanelSlide(View panel, float slideOffset) {
            super.onPanelSlide(panel, slideOffset);
            if (partialView == null || fullView == null) {
                return;
            }

            updateVisibility(slideOffset);

            setAlpha(partialView, 1 - slideOffset); // only top view should fade
//      setAlpha(fullView, slideOffset); // full view should be opaque anyway
            // this could save some overdraw
        }
    };

    private void updateVisibility(float slideOffset) {
        if (Build.VERSION.SDK_INT < 11) {
            updateVisibilityBase(slideOffset);
        } else {
            updateVisibilityHoneycomb(slideOffset == 1);
        }
    }

    private void updateVisibility(boolean visible) {
        if (Build.VERSION.SDK_INT < 11) {
            updateVisibilityBase(visible);
        } else {
            updateVisibilityHoneycomb(visible);
        }
    }

    private void updateVisibilityBase(float slideOffset) {
        if (slideOffset == 1 && !mWasOpened) {
            updateVisibilityBase(true);
            mWasOpened = true;
        } else if (slideOffset < 1 && mWasOpened) {
            updateVisibilityBase(false);
            mWasOpened = false;
        }
    }

    /**
     * Pre-Honeycomb the views have to be physically repositioned otherwise they still listen
     * on original places for touch.
     * Curiously this happened here even when visibility was set to gone.
     *
     * @param visible
     */
    private void updateVisibilityBase(boolean visible) {
        if (visible) {
            partialView.layout(-partialView.getWidth(), 0, 0, partialView.getHeight());
        } else {
            partialView.layout(0, 0, partialView.getWidth(), partialView.getHeight());
        }
    }

    private void updateVisibilityHoneycomb(boolean visible) {
        partialView.setVisibility(visible ? View.GONE : VISIBLE);
    }

    @TargetApi(11)
    private static void setAlpha(View view, float alpha) {
        if (Build.VERSION.SDK_INT >= 11) {
            view.setAlpha(alpha);
        } else {
            ViewHelper.setAlpha(view, alpha);
        }
    }
}