Java tutorial
/* * Copyright (C) 2015 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.support.design.widget; import android.content.Context; import android.graphics.Rect; import android.support.design.widget.CoordinatorLayout.Behavior; import android.support.v4.view.GravityCompat; import android.support.v4.view.ViewCompat; import android.support.v4.view.WindowInsetsCompat; import android.util.AttributeSet; import android.view.Gravity; import android.view.View; import android.view.ViewGroup; import java.util.List; /** * The {@link Behavior} for a scrolling view that is positioned vertically below another view. * See {@link HeaderBehavior}. */ abstract class HeaderScrollingViewBehavior extends ViewOffsetBehavior<View> { final Rect mTempRect1 = new Rect(); final Rect mTempRect2 = new Rect(); private int mVerticalLayoutGap = 0; private int mOverlayTop; public HeaderScrollingViewBehavior() { } public HeaderScrollingViewBehavior(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean onMeasureChild(CoordinatorLayout parent, View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed) { final int childLpHeight = child.getLayoutParams().height; if (childLpHeight == ViewGroup.LayoutParams.MATCH_PARENT || childLpHeight == ViewGroup.LayoutParams.WRAP_CONTENT) { // If the menu's height is set to match_parent/wrap_content then measure it // with the maximum visible height final List<View> dependencies = parent.getDependencies(child); final View header = findFirstDependency(dependencies); if (header != null) { if (ViewCompat.getFitsSystemWindows(header) && !ViewCompat.getFitsSystemWindows(child)) { // If the header is fitting system windows then we need to also, // otherwise we'll get CoL's compatible measuring ViewCompat.setFitsSystemWindows(child, true); if (ViewCompat.getFitsSystemWindows(child)) { // If the set succeeded, trigger a new layout and return true child.requestLayout(); return true; } } int availableHeight = View.MeasureSpec.getSize(parentHeightMeasureSpec); if (availableHeight == 0) { // If the measure spec doesn't specify a size, use the current height availableHeight = parent.getHeight(); } final int height = availableHeight - header.getMeasuredHeight() + getScrollRange(header); final int heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height, childLpHeight == ViewGroup.LayoutParams.MATCH_PARENT ? View.MeasureSpec.EXACTLY : View.MeasureSpec.AT_MOST); // Now measure the scrolling view with the correct height parent.onMeasureChild(child, parentWidthMeasureSpec, widthUsed, heightMeasureSpec, heightUsed); return true; } } return false; } @Override protected void layoutChild(final CoordinatorLayout parent, final View child, final int layoutDirection) { final List<View> dependencies = parent.getDependencies(child); final View header = findFirstDependency(dependencies); if (header != null) { final CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams(); final Rect available = mTempRect1; available.set(parent.getPaddingLeft() + lp.leftMargin, header.getBottom() + lp.topMargin, parent.getWidth() - parent.getPaddingRight() - lp.rightMargin, parent.getHeight() + header.getBottom() - parent.getPaddingBottom() - lp.bottomMargin); final WindowInsetsCompat parentInsets = parent.getLastWindowInsets(); if (parentInsets != null && ViewCompat.getFitsSystemWindows(parent) && !ViewCompat.getFitsSystemWindows(child)) { // If we're set to handle insets but this child isn't, then it has been measured as // if there are no insets. We need to lay it out to match horizontally. // Top and bottom and already handled in the logic above available.left += parentInsets.getSystemWindowInsetLeft(); available.right -= parentInsets.getSystemWindowInsetRight(); } final Rect out = mTempRect2; GravityCompat.apply(resolveGravity(lp.gravity), child.getMeasuredWidth(), child.getMeasuredHeight(), available, out, layoutDirection); final int overlap = getOverlapPixelsForOffset(header); child.layout(out.left, out.top - overlap, out.right, out.bottom - overlap); mVerticalLayoutGap = out.top - header.getBottom(); } else { // If we don't have a dependency, let super handle it super.layoutChild(parent, child, layoutDirection); mVerticalLayoutGap = 0; } } float getOverlapRatioForOffset(final View header) { return 1f; } final int getOverlapPixelsForOffset(final View header) { return mOverlayTop == 0 ? 0 : MathUtils.constrain((int) (getOverlapRatioForOffset(header) * mOverlayTop), 0, mOverlayTop); } private static int resolveGravity(int gravity) { return gravity == Gravity.NO_GRAVITY ? GravityCompat.START | Gravity.TOP : gravity; } abstract View findFirstDependency(List<View> views); int getScrollRange(View v) { return v.getMeasuredHeight(); } /** * The gap between the top of the scrolling view and the bottom of the header layout in pixels. */ final int getVerticalLayoutGap() { return mVerticalLayoutGap; } /** * Set the distance that this view should overlap any {@link AppBarLayout}. * * @param overlayTop the distance in px */ public final void setOverlayTop(int overlayTop) { mOverlayTop = overlayTop; } /** * Returns the distance that this view should overlap any {@link AppBarLayout}. */ public final int getOverlayTop() { return mOverlayTop; } }