1. 创建AlertDialog：
View view= LayoutInflater.from(RegActivity.this).inflate(R.layout.layout_error_dialog,null);
AlertDialog dialog=new AlertDialog.Builder(RegActivity.this)
.setView(view)
.create();
2. 添加动画
dialog.getWindow().setWindowAnimations(R.style.mystyle);
dialog.show();
3. style:
<style name="mystyle" parent="@android:style/Animation">
<item name="android:windowEnterAnimation">@anim/dialog_anim_appear</item>
<item name="android:windowExitAnimation">@anim/dialog_anim_disappear</item>
</style>
dialog_anim_appear：
<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
<scale
android:fromXScale="0"
android:toXScale="1"
android:fromYScale="0"
android:toYScale="1"
android:pivotX="50%p"
android:pivotY="50%p"
android:duration="300"
/>
</set>
dialog_anim_disappear：
<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
<translate
android:duration="500"
android:toYDelta="100.0%p" />
<alpha
android:duration="500"
android:fromAlpha="0.5"
android:interpolator="@android:anim/accelerate_interpolator"
android:toAlpha="1.0" />
</set>
