問題來源
最近用了下RecyclerView,很好用，每個item我設定的是CardView包含一個TextView,

<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_margin="8dp"
 

    android:id="@+id/cv_item"
    card_view:cardCornerRadius="4dp">

    <TextView
        android:id="@+id/text_view"
        android:padding="20dp"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</android.support.v7.widget.CardView>

這樣就可以顯示cardview了，問題是給item新增一個selector

解決
1 類似Button直接在drawable下新建個card_selector.xml佈局，然後設定CardView背景：

android:background="@drawable/card_selector"

然，，沒有什麼用。。

給CardView添加個前景：

android:foreground="?android:attr/selectableItemBackground"

這樣就可以了，在5.0以上的裝置上有點選有波紋效果，5.0以下無波紋，只有前景色變化

3 自定義CardView前景

Android-L CardView Visual Touch Feedback

• 設定CardView自定義的前景：

android:foreground="@drawable/card_foreground"

• 5.0之後

  drawable-v21/card_foreground.xml

<ripple xmlns:android="http://schemas.android.com/apk/res/android" 
        android:color="#20000000"
        android:drawable="@drawable/card_foreground_selector" />

drawable-v21/card_foreground_selector.xml

<ripple xmlns:android="http://schemas.android.com/apk/res/android" 
        android:color="#20000000"
        android:drawable="@drawable/card_foreground_selector" />
drawable-v21/card_foreground_selector.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true">
        <shape android:shape="rectangle">
            <solid android:color="#18ffc400"/>
        </shape>
    </item>
    <item android:state_focused="true" android:state_enabled="true">
        <shape android:shape="rectangle">
            <solid android:color="#0f000000"/>
        </shape>
    </item>
</selector>

• 5.0之前
  drawable/card_foreground.xml

<inset xmlns:android="http://schemas.android.com/apk/res/android" 
    android:drawable="@drawable/card_foreground_selector"
    android:insetLeft="2dp"
    android:insetRight="2dp"
    android:insetTop="4dp"
    android:insetBottom="4dp"/>

drawable/card_foreground_selector.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true">
        <shape android:shape="rectangle">
            <solid android:color="#1838f508"/>
            <corners android:radius="@dimen/card_radius" />
        </shape>
    </item>
    <item android:state_focused="true" android:state_enabled="true">
        <shape android:shape="rectangle">
            <solid android:color="#0f000000"/>
            <corners android:radius="@dimen/card_radius" />
        </shape>
    </item>
</selector>

效果：

• 直接設定selector也是可以的：

android:foreground="@drawable/card_foreground_selector"