Android CoordinatorLayout + AppBarLayout(向上滚动隐藏指定的View)

在新的Android Support Library里面,新增了CoordinatorLayout, AppBarLayout等.

实现的效果: 向下滚动RecylerView,Tab会被隐藏,向上滚动RecylerView,Tab恢复出现.这么做的好处在于,用户能有更多的空间位置去看列表里面的内容.

实现步骤:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <android.support.v7.widget.Toolbar
            android:id="@+id/third_activity_toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"/>

        <android.support.design.widget.TabLayout
            android:id="@+id/tab_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:layout_scrollFlags="scroll|enterAlways"
            app:tabIndicatorColor="@color/medium_blue"
            app:tabSelectedTextColor="@color/medium_blue"
            app:tabTextAppearance="@style/TabText"
            app:tabTextColor="@color/gray_text"/>

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"/>

</android.support.design.widget.CoordinatorLayout>    

1) 首先需要用CoordinatorLayout包住AppBarLayout;

2) 顶部区域的View都放在AppBarLayout里面;

3) AppBarLayout外面,CoordinatorLayout里面,放一个带有可滚动的View.如上的例子,放的是ViewPager,而ViewPager里面是放了RecylerView的,即是可以滚动的View.

4) 在AppBarLayout里面的View,通过app:layout_scrollFlags属性来控制,滚动时候的表现.其中有4种Flag的类型.

• scroll: this flag should be set for all views that want to scroll off the screen - for views that do not use this flag, they’ll remain pinned to the top of the screen
• enterAlways: this flag ensures that any downward scroll will cause this view to become visible, enabling the ‘quick return’ pattern
• enterAlwaysCollapsed: When your view has declared a minHeight and you use this flag, your View will only enter at its minimum height (i.e., ‘collapsed’), only re-expanding to its full height when the scrolling view has reached it’s top.
• exitUntilCollapsed: this flag causes the view to scroll off until it is ‘collapsed’ (its minHeight) before exiting

上面的例子种用的是 scroll 和 enterAlways.

Scroll 表示向下滚动时,这个View会被滚出屏幕范围直到隐藏.

enterAlways 表示向上滚动时,这个View会随着滚动手势出现,直到恢复原来的位置.

5) 在可以滚动的View上设置属性 app:layout_behavior.

该属性的值实际上是一个完整的class名字,而上面例子中的 @string/appbar_scrolling_view_behavior 是Android Support Library 定义后的值,可以被直接使用.

这个Behavior的class是真正控制滚动时候View的滚动行为.我们也可以继承Behavior这个class去实现特有的滚动行为.

6) 代码部分,只需要实现RecylerView的逻辑就可以了.