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Ⅶ. Animate View State Changes / 视图状态动画

介绍

所谓视图状态动画，就是 View 在状态改变时执行的动画效果。和之前我们通过 selector 选择器给 Button 设置不同状态下的背景效果是一样一样的。

咱先看一下实现的一种效果图(点击时Z轴抬高):

点击时Z轴抬高

使用

因为视图状态动画是在 View 不同的状态下产生的动画效果，所以我们先来看一下 View 都有哪些状态：

State 说明
android:constantSize If true, the drawable's reported internal size will remain constant as the state changes; the size is the maximum of all of the states.
android:state_activated State value for StateListDrawable, set when a view or its parent has been "activated" meaning the user has currently marked it as being of interest.
android:state_active State value for StateListDrawable.
android:state_checkable State identifier indicating that the object may display a check mark.
android:state_checked State identifier indicating that the object is currently checked.
android:state_enabled State value for StateListDrawable, set when a view is enabled.
android:state_first State value for StateListDrawable.
android:state_focused State value for StateListDrawable, set when a view has input focus.
android:state_last State value for StateListDrawable.
android:state_middle State value for StateListDrawable.
android:state_pressed State value for StateListDrawable, set when the user is pressing down in a view.
android:state_selected State value for StateListDrawable, set when a view (or one of its parents) is currently selected.
android:state_single State value for StateListDrawable.
android:state_window_focused State value for StateListDrawable, set when a view's window has input focus.
android:variablePadding If true, allows the drawable's padding to change based on the current state that is selected.
android:visible Indicates whether the drawable should be initially visible.

小提示(关于在 selector 中设置不同状态的 item 时匹配原则的一个细节): 如果有多个item，那么程序将自动从上到下进行匹配，最先匹配的将得到应用。（不是通过最佳匹配） 如果一个item没有任何的状态说明，那么它将可以被任何一个状态匹配。

View 状态改变的动画主要是两个类：

  1. StateListAnimator 是个动画, 在 res/anim (或者 res/animator)中
  2. AnimatedStateListDrawable 是个 Drawable, 在 res/drawable 中。

ps:这里的 StateListAnimator 大多教程都说放在 res/anim 目录下，放在此目录下能够正常使用，但在 AS3.0.1 中会有警示 <selector> XML file should be in either "animator" or "drawable", not "anim" 。
我尝试放到 res/animator 后不再有警示，并且完全不影响使用。所以这里建议大家以后都放到此目录下。

StateListAnimator

xml文件：你可以改成任意一种objectAnimator动画。 这里使用的是translationZ

<!-- animate the translationZ property of a view when pressed -->
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true">
    <set>
      <objectAnimator android:propertyName="translationZ"
        android:duration="@android:integer/config_shortAnimTime"
        android:valueTo="2dp"
        android:valueType="floatType"/>
        <!-- you could have other objectAnimator elements
             here for "x" and "y", or other properties -->
    </set>
  </item>
  
  <item android:state_enabled="true"
    android:state_pressed="false"
    android:state_focused="true">
    <set>
      <objectAnimator android:propertyName="translationZ"
        android:duration="100"
        android:valueTo="0"
        android:valueType="floatType"/>
    </set>
  </item>
</selector>

代码中加载：

//加载动画
StateListAnimator stateLAnim = AnimatorInflater.loadStateListAnimator(this,R.anim.elevation);   
//设置动画
tv_elevation.setStateListAnimator(stateLAnim);

xml 中使用：

使用 android:stateListAnimator 属性将此动画分配给您的视图。

AnimatedStateListDrawable

xml布局：这个效果有点意思（ps:但没卵用啊，目前我是没有发现那种场景可以使用）
当你是 pressed 状态的时候 animation-list 正着走一遍，drawable 使用最后一个。
当你是 default 状态时 animation-list 反着走一遍，drawable 使用第一个。

res/drawable/myanimstatedrawable

<?xml version="1.0" encoding="utf-8"?>
<animated-selector 
    xmlns:android="http://schemas.android.com/apk/res/android" >

    <!-- provide a different drawable for each state -->
    <item
        android:id="@+id/pressed"
        android:drawable="@drawable/btn_pressed"
        android:state_pressed="true"/>
    <!-- <item
        android:id="@+id/focused"
        android:drawable="@drawable/btn_focused"
        android:state_focused="true"/> -->
    <item
        android:id="@id/default1"
        android:drawable="@drawable/btn_default"/>

    <!-- specify a transition -->
    <transition
        android:fromId="@+id/default1"
        android:toId="@+id/pressed" >
        <animation-list>
            <item
                android:drawable="@drawable/con_time_tk"
                android:duration="500"/>
            <item
                android:drawable="@drawable/btn_default"
                android:duration="500"/>
            <item
                android:drawable="@drawable/btn_focused"
                android:duration="500"/>
            <item
                android:drawable="@drawable/btn_pressed"
                android:duration="500"/>
            <item
                android:drawable="@drawable/con_time_xm"
                android:duration="500"/>
            <item
                android:drawable="@drawable/con_time_tk"
                android:duration="500"/>
        </animation-list>
    </transition>
</animated-selector>

xml文件作为控件的背景使用。

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