Android可折叠标题栏的使用

AppBarLayout使用

官方文档

1.AppBarLayout is a vertical LinearLayout which implements many of the features of material designs app bar concept, namely scrolling gestures.
2.Children should provide their desired scrolling behavior through setScrollFlags(int) and the associated layout xml attribute:app:layout_scrollFlags.
3.This view depends heavily on being used as a direct child within a CoordinatorLayout. If you use AppBarLayout within a different ViewGroup, most of it's functionality will not work.
3.AppBarLayout also requires a separate scrolling sibling in order to know when to scroll. The binding is done through the AppBarLayout.ScrollingViewBehavior behavior class, meaning that you should set your scrolling view's behavior to be an instance of AppBarLayout.ScrollingViewBehavior. A string resource containing the full class name is available.

AppBarLayout是一种支持响应滚动手势的app bar布局（比如工具栏滚出或滚入屏幕），严重依赖CoordinatorLayout,并且作为CoordinatorLayout的直接子View来使用.AppBarLayout的子布局有5种滚动标识,通过配置属性app:layout_scrollFlags来使用：

（1） scroll:The view will be scroll in direct relation to scroll events. This flag needs to be set for any of the other flags to take effect. If any sibling views before this one do not have this flag, then this value has no effect.

将此布局和滚动事件关联。这个标识要设置在其他标识之前，没有这个标识则布局不会滚动且其他标识设置无效。

（2）enterAlways: When entering (scrolling on screen) the view will scroll on any downwards scroll event, regardless of whether the scrolling view is also scrolling. This is commonly referred to as the 'quick return' pattern.

任何向下滚动操作都会使此布局可见。这个标识通常被称为“快速返回”模式。

（3）exitUntilCollapsed：When exiting (scrolling off screen) the view will be scrolled until it is 'collapsed'. The collapsed height is defined by the view's minimum height.

View要往上逐渐“消逝”时，会一直往上滑动，直到剩下的的高度达到它的最小高度后，再响应ScrollView的内部滑动事件。

（4）enterAlwaysCollapsed：An additional flag for 'enterAlways' which modifies the returning view to only initially scroll back to it's collapsed height. Once the scrolling view has reached the end of it's scroll range, the remainder of this view will be scrolled into view. The collapsed height is defined by the view's minimum height.

跟enterAlways一起使用，它是指，View在往下“出现”的时候，首先是enterAlways效果，当View的高度达到最小高度时，View就暂时不去往下滚动，直到ScrollView滑动到顶部不再滑动时，View再继续往下滑动，直到滑到View的顶部结束。

（5）snap：Upon a scroll ending, if the view is only partially visible then it will be snapped and scrolled to it's closest edge. For example, if the view only has it's bottom 25% displayed, it will be scrolled off screen completely. Conversely, if it's bottom 75% is visible then it will be scrolled fully into view.

当你停止滑到屏幕时，控件自动恢复原样或者自动滑到底。

CollapsingToolbarLayout使用

官方文档

CollapsingToolbarLayout is a wrapper for Toolbar which implements a collapsing app bar. It is designed to be used as a direct child of a AppBarLayout.CollapsingToolbarLayout contains the following features:

CollapsingToolbarLayout的子布局有3种折叠模式（Toolbar中设置的app:layout_collapseMode）
(1) parallax:子View可以选择在当前的布局当时是否以“视差”的方式来跟随滚动。（PS:其实就是让这个View的滚动的速度比其他正常滚动的View速度稍微慢一点）。
(2)pin:(官网原文:The view will pin in place until it reaches the bottom of the CollapsingToolbarLayout.) 将子View位置固定(Pinned position children)：子View可以选择是否在全局空间上固定位置，这对于Toolbar来说非常有用，因为当布局在移动时，可以将Toolbar固定位置而不受移动的影响。
(3)none：这个是默认属性，布局将正常显示，没有折叠的行为。
layout_collapseParallaxMultiplier属性:
视差滚动子系数,取值的范围是0~1。假如把ImageView这个属性设置成0.7，那么当这个图片有70%被收缩时，松开手指不点击屏幕，该图片会自动收缩。