1 package com.android.launcher3.allapps.search; 2 3 import android.content.res.Resources; 4 import android.graphics.Outline; 5 import android.support.v7.widget.RecyclerView; 6 import android.view.View; 7 import android.view.ViewGroup; 8 import android.view.ViewOutlineProvider; 9 10 import com.android.launcher3.BaseRecyclerView; 11 import com.android.launcher3.R; 12 13 /** 14 * Helper class for controlling the header elevation in response to RecyclerView scroll. 15 */ 16 public class HeaderElevationController extends RecyclerView.OnScrollListener { 17 18 private final View mHeader; 19 private final View mHeaderChild; 20 private final float mMaxElevation; 21 private final float mScrollToElevation; 22 23 private int mCurrentY = 0; 24 25 public HeaderElevationController(View header) { 26 mHeader = header; 27 final Resources res = mHeader.getContext().getResources(); 28 mMaxElevation = res.getDimension(R.dimen.all_apps_header_max_elevation); 29 mScrollToElevation = res.getDimension(R.dimen.all_apps_header_scroll_to_elevation); 30 31 // We need to provide a custom outline so the shadow only appears on the bottom edge. 32 // The top, left and right edges are all extended out to match parent's edge, so that 33 // the shadow is clipped by the parent. 34 final ViewOutlineProvider vop = new ViewOutlineProvider() { 35 @Override 36 public void getOutline(View view, Outline outline) { 37 // Set the left and top to be at the parents edge. Since the coordinates are 38 // relative to this view, 39 // (x = -view.getLeft()) for this view => (x = 0) for parent 40 final int left = -view.getLeft(); 41 final int top = -view.getTop(); 42 43 // Since the view is centered align, the spacing on left and right are same. 44 // Add same spacing on the right to reach parent's edge. 45 final int right = view.getWidth() - left; 46 final int bottom = view.getHeight(); 47 final int offset = (int) mMaxElevation; 48 outline.setRect(left - offset, top - offset, right + offset, bottom); 49 } 50 }; 51 mHeader.setOutlineProvider(vop); 52 mHeaderChild = ((ViewGroup) mHeader).getChildAt(0); 53 } 54 55 public void reset() { 56 mCurrentY = 0; 57 onScroll(mCurrentY); 58 } 59 60 @Override 61 public final void onScrolled(RecyclerView recyclerView, int dx, int dy) { 62 mCurrentY = ((BaseRecyclerView) recyclerView).getCurrentScrollY(); 63 onScroll(mCurrentY); 64 } 65 66 private void onScroll(int scrollY) { 67 float elevationPct = Math.min(scrollY, mScrollToElevation) / mScrollToElevation; 68 float newElevation = mMaxElevation * elevationPct; 69 if (Float.compare(mHeader.getElevation(), newElevation) != 0) { 70 mHeader.setElevation(newElevation); 71 72 // To simulate a scrolling effect for the header, we translate the header down, and 73 // its content up by the same amount, so that it gets clipped by the parent, making it 74 // look like the content was scrolled out of the view. 75 int shift = Math.min(mHeader.getHeight(), scrollY); 76 mHeader.setTranslationY(-shift); 77 mHeaderChild.setTranslationY(shift); 78 } 79 } 80 81 } 82
