Android属性动画-Property Animation(二) 使用ObjectAnimator完成动画

     上一篇文章中我们分析了属性动画的工作原理，这篇文章开始介绍属性动画的实现，就不会再去分析原理，如果对原理不清楚的朋友可以看一下 Android属性动画-Property Animation(一) 原理分析

       使用属性动画时我们通常使用Animator的两个子类，ValueAnimator和ObjectAnimator。这两个子类如何选择呢？在大多数情况下我们会使用ObjectAnimator,它比较轻量级，使用非常简单，但是它也有一些局限性，就是必须要实现属性的getter和setter方法，因为使用ValueAnimator的时候我们必须实现ValueAnimator.AnimatorUpdateListener接口，并且在onAnimationUpdate()里面手动更新属性值，而ObjectAnimator不用，那么他就必须要通过setter方法自动给属性赋值，getter方法自动获得属性的值。

       因为ObjectAnimator使用的比较多，使用起来又比较简单，我们就先来分析一下ObjectAnimator怎么使用吧

       其实ObjectAnimator是ValueAnimator的一个子类，既然google这样设计，那么它肯定进行了某方面的优化，我们上面已经提到了，使用ObjectAnimator不用再去实现ValueAnimator.AnimatorUpdateListener接口了，因为他会自动去更新属性值。
我们先来看一个简单的例子：

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/** * 作者： 阿拉灯神灯 * 主页：http://blog.youkuaiyun.com/nugongahou110 * 日期：2015.07.02 */ public class MainActivity extends Activity { private Button mButton ; @Override protected void onCreate ( Bundle savedInstanceState ) { super . onCreate ( savedInstanceState ); setContentView ( R . layout . activity_main ); mButton =( Button ) findViewById ( R . id . start_my_anim ); mButton . setOnClickListener ( new OnClickListener () { @Override public void onClick ( View v ) { //新建一个ObjectAnimator实例，使用它的静态方法ofFloat //第一个参数是要执行动画的对象 //第二个参数是要改变属性的名称 //第三个参数是属性的初始值，第四个参数是属性的结束值 ObjectAnimator anim = ObjectAnimator . ofFloat ( mButton , "scaleY" , 1.0f , 3.0f ); // ObjectAnimator anim = ObjectAnimator.ofFloat(mButton, "scaleY", 3.0f); // ObjectAnimator anim = ObjectAnimator.ofFloat(mButton, "scaley", 3.0f); //设置一个TimeInterpolator为弹球效果 anim . setInterpolator ( new BounceInterpolator ()); //设置动画持续时间 anim . setDuration ( 2000 ); //开始动画 anim . start (); } }); } }

 来自CODE的代码片

MainActivity.java

我们看上面代码中的“scaleY”,这是怎么来的呢？不是说ObjectAnimator需要给属性设置setter/getter方法吗？我们也没设置啊，怎么也可以执行？

带着这些疑问我们一步一步去分析一下，首先执行动画的是一个Button，Button是继承自TextView的，TextView是继承自View的。我们到View中去看一看。

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public void setScaleX ( float scaleX ) { ensureTransformationInfo (); final TransformationInfo info = mTransformationInfo ; if ( info . mScaleX != scaleX ) { invalidateViewProperty ( true , false ); info . mScaleX = scaleX ; info . mMatrixDirty = true ; invalidateViewProperty ( false , true ); if ( mDisplayList != null ) { mDisplayList . setScaleX ( scaleX ); } if (( mPrivateFlags2 & PFLAG2_VIEW_QUICK_REJECTED ) == PFLAG2_VIEW_QUICK_REJECTED ) { // View was rejected last time it was drawn by its parent; this may have changed invalidateParentIfNeeded (); } } } public float getScaleX () { return mTransformationInfo != null ? mTransformationInfo . mScaleX : 1 ; }

 来自CODE的代码片

View.java

果然，在View中已经写好了scaleY的setter和getter方法，不用我们自己去写了。除此之外，View中还已经写好了setAlpha()、setX()、setScaleX()、setTranslationX()等setter方法和对应的getter方法，我们可以拿来就用，其实这些不就是View Animation中的淡入淡出，平移，放大缩小等动画吗！

       Note：如果将第24行注释掉，执行第25行。我们发现后面只有一个参数3.0f，属性的初始值没有了，照样可以执行！ObjectAnimator可以自动调用getter方法，获得当前属性的值，这就是为什么一定要有getter方法！如果将24、25行都注释掉，执行第26行，那就该报错了，因为View中没有一个"scaley"这个属性，只有"scaleY"。大小写非常重要！具体命名规则见下例

但是作为属性动画，号称是可以改变任意一个属性的，那么我们就来自定义一个属性，看看属性动画的威力！

首先我们自定义一个布局，它继承自View，目的就是画出一个数字在屏幕上

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public class TempView extends View { //新建一个画笔 private Paint paint = new Paint (); //这个就是在屏幕上显示的数字 private int mCurnum = 0 ; public TempView ( Context context , AttributeSet attrs , int defStyle ) { super ( context , attrs , defStyle ); } public TempView ( Context context , AttributeSet attrs ) { super ( context , attrs ); } public TempView ( Context context ) { super ( context ); } //setter方法，这个方法必须要有，而且命名规则不能错！ //我们在启动动画的时候，传进去了一个字符串表示要计算的属性 //ObjectAnimator anim = ObjectAnimator.ofInt(mView,"curnum",100); //就是"curnum"！ 那么根据命名规则，我们就要写一个setCurnum()方法,系统会自动找到这个setter方法 //如果我们传入的字符串为"aladengshendeng"，那么我们就要写一个setAladengshendeng()方法 //明白了吧，只要将首字母大写后的字符串加在set的后面，这个setter方法的命名才是正确的！！ public void setCurnum ( int currnum ){ mCurnum = currnum ; //这个invalidate方法一定要有！！它会重新调用onDraw()方法。这个是通知系统我的属性已经改变！你要将我重画！ invalidate (); } //getter方法，这个方法必须要有，命名规则同setter方法 public float getCurnum (){ return mCurnum ; } @Override protected void onDraw ( Canvas canvas ) { // super.onDraw(canvas); paint . setStrokeWidth ( 8 ); paint . setTextSize ( 100 ); canvas . drawText ( String . valueOf ( mCurnum ), 100 , 100 , paint ); } }

 来自CODE的代码片

TempView.java

布局文件

<a target=_blank id="L1" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L1" rel="#L1" style="color: rgb(102, 102, 102); text-decoration: none;"> 1</a> <a target=_blank id="L2" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L2" rel="#L2" style="color: rgb(102, 102, 102); text-decoration: none;"> 2</a> <a target=_blank id="L3" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L3" rel="#L3" style="color: rgb(102, 102, 102); text-decoration: none;"> 3</a> <a target=_blank id="L4" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L4" rel="#L4" style="color: rgb(102, 102, 102); text-decoration: none;"> 4</a> <a target=_blank id="L5" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L5" rel="#L5" style="color: rgb(102, 102, 102); text-decoration: none;"> 5</a> <a target=_blank id="L6" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L6" rel="#L6" style="color: rgb(102, 102, 102); text-decoration: none;"> 6</a> <a target=_blank id="L7" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L7" rel="#L7" style="color: rgb(102, 102, 102); text-decoration: none;"> 7</a> <a target=_blank id="L8" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L8" rel="#L8" style="color: rgb(102, 102, 102); text-decoration: none;"> 8</a> <a target=_blank id="L9" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L9" rel="#L9" style="color: rgb(102, 102, 102); text-decoration: none;"> 9</a> <a target=_blank id="L10" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L10" rel="#L10" style="color: rgb(102, 102, 102); text-decoration: none;"> 10</a> <a target=_blank id="L11" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L11" rel="#L11" style="color: rgb(102, 102, 102); text-decoration: none;"> 11</a> <a target=_blank id="L12" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L12" rel="#L12" style="color: rgb(102, 102, 102); text-decoration: none;"> 12</a> <a target=_blank id="L13" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L13" rel="#L13" style="color: rgb(102, 102, 102); text-decoration: none;"> 13</a> <a target=_blank id="L14" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L14" rel="#L14" style="color: rgb(102, 102, 102); text-decoration: none;"> 14</a> <a target=_blank id="L15" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L15" rel="#L15" style="color: rgb(102, 102, 102); text-decoration: none;"> 15</a> <a target=_blank id="L16" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L16" rel="#L16" style="color: rgb(102, 102, 102); text-decoration: none;"> 16</a> <a target=_blank id="L17" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L17" rel="#L17" style="color: rgb(102, 102, 102); text-decoration: none;"> 17</a> <a target=_blank id="L18" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L18" rel="#L18" style="color: rgb(102, 102, 102); text-decoration: none;"> 18</a> <a target=_blank id="L19" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L19" rel="#L19" style="color: rgb(102, 102, 102); text-decoration: none;"> 19</a> <a target=_blank id="L20" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L20" rel="#L20" style="color: rgb(102, 102, 102); text-decoration: none;"> 20</a> <a target=_blank id="L21" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L21" rel="#L21" style="color: rgb(102, 102, 102); text-decoration: none;"> 21</a> <a target=_blank id="L22" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L22" rel="#L22" style="color: rgb(102, 102, 102); text-decoration: none;"> 22</a> <a target=_blank id="L23" href="http://blog.youkuaiyun.com/nugongahou110/article/details/46722595#L23" rel="#L23" style="color: rgb(102, 102, 102); text-decoration: none;"> 23</a>

<RelativeLayout xmlns:android= "http://schemas.android.com/apk/res/android" xmlns:tools= "http://schemas.android.com/tools" android:layout_width= "match_parent" android:layout_height= "match_parent" > <com.example.objectanimationdemo1.TempView android:id= "@+id/mView" android:layout_width= "wrap_content" android:layout_height= "wrap_content" /> <Button android:id= "@+id/bt_start_animation" android:layout_width= "wrap_content" android:layout_height= "wrap_content" android:layout_alignParentBottom= "true" android:layout_alignParentRight= "true" android:text= "start!" /> </RelativeLayout>

 来自CODE的代码片

main_activity.xml

最后是MainActivity

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public class MainActivity extends Activity { private TempView mView ; private Button startAnimation ; @Override protected void onCreate ( Bundle savedInstanceState ) { super . onCreate ( savedInstanceState ); setContentView ( R . layout . activity_main ); mView =( TempView ) findViewById ( R . id . mView ); startAnimation =( Button ) findViewById ( R . id . bt_start_animation ); startAnimation . setOnClickListener ( new OnClickListener () { @Override public void onClick ( View v ) { //新建一个ObjectAnimator实例，调用静态方法ofInt() //第一个参数是要执行动画的对象，即我们自定义的TempView //第二个参数是我们想要改变的属性名，TempView中要有相应的setter/getter方法 //第三个参数是我们给定curnum的结束值，至于为什么没有开始值，以及需不需要有开始值，请参看上面的例子 ObjectAnimator anim = ObjectAnimator . ofInt ( mView , "curnum" , 100 ); //设置动画的持续时间 anim . setDuration ( 5000 ); //设置一个TimeInterpolator为减速 anim . setInterpolator ( new DecelerateInterpolator ()); //开始动画 anim . start (); } }); } }

 来自CODE的代码片

MainActivity.java

最后的效果：

怎么样，属性动画很厉害吧。这可是View Animation做不了的！

 ObjectAnimator我们就分析完了，下一篇我们来分析ValueAnimator Android属性动画-Property Animation(三) 使用ValueAnimator完成动画 



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