該效果通常以background的形式呈現(xiàn)，在XML中可以引用以下兩個系統(tǒng)自帶屬性：

android:background="?android:attr/selectableItemBackground" 有邊界波紋
android:background="?android:attr/··" 超出邊界波紋。該波紋由父布局繪制及限制邊界(API 21提供)
以selectableItemBackground為例看下系統(tǒng)屬性的實現(xiàn)原理，發(fā)現(xiàn)該屬性的定義最終指向<item name="selectableItemBackground">@drawable/item_background_material</item>,
查看該Drawable文件內(nèi)容為：

<ripple xmlns:android="http://schemas.android.com/apk/res/android"
    android:color="?attr/colorControlHighlight">
    <item android:id="@id/mask">
        <color android:color="@color/white" />
    </item>
</ripple>

selectableItemBackgroundBorderless所對應Drawable內(nèi)容為：

<ripple xmlns:android="http://schemas.android.com/apk/res/android" android:color="?attr/colorControlHighlight" />

ripple類型的xml會創(chuàng)建RippleDrawable

    private Drawable inflateFromTag(@NonNull String name) {
        switch (name) {
            case "selector":
                return new StateListDrawable();
            case "animated-selector":
                return new AnimatedStateListDrawable();
            case "level-list":
                return new LevelListDrawable();
            case "layer-list":
                return new LayerDrawable();
            case "transition":
                return new TransitionDrawable();
            case "ripple":
                return new RippleDrawable();
            case "adaptive-icon":
                return new AdaptiveIconDrawable();
            case "color":
                return new ColorDrawable();
            case "shape":
                return new GradientDrawable();
            case "vector":
                return new VectorDrawable();
            case "animated-vector":
                return new AnimatedVectorDrawable();
            case "scale":
                return new ScaleDrawable();
            case "clip":
                return new ClipDrawable();
            case "rotate":
                return new RotateDrawable();
            case "animated-rotate":
                return new AnimatedRotateDrawable();
            case "animation-list":
                return new AnimationDrawable();
            case "inset":
                return new InsetDrawable();
            case "bitmap":
                return new BitmapDrawable();
            case "nine-patch":
                return new NinePatchDrawable();
            default:
                return null;
        }
    }

作者：七號大蒜
鏈接：http://www.itdecent.cn/p/665c9d85c21d
來源：簡書
簡書著作權歸作者所有，任何形式的轉載都請聯(lián)系作者獲得授權并注明出處。