占位符 可以帮助我们设置一些不同项目中 不同属性的值
比如最近遇到有的项目中需要取消多屏模式 有的项目需要多屏模式
那么我们可以这么设置

  <activity
            android:name=".MainActivity"
            android:alwaysRetainTaskState="true"
            android:excludeFromRecents="true"
            android:exported="true"
            android:launchMode="singleTop"
            android:resizeableActivity="${resizeable}"
            android:screenOrientation="landscape"
            android:windowSoftInputMode="adjustPan">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

在gradle中 
  productFlavors {

         s202h {
             dimension "program"
             buildConfigField("String", "CHANNEL_ID", "\"000302\"")
             buildConfigField("String", "APP_ID","\"\"")
             manifestPlaceholders.put("resizeable","true")
         }
         s302ica {
             dimension "program"
             buildConfigField("String", "CHANNEL_ID", "\"000302\"")
             buildConfigField("String", "APP_ID","\"c7d8cc46cf755998719d0c353297c4cfe803ccf5\"")
             buildConfigField("String", "APP_ID_USER","\"c7d8cc46cf755998719d0c353297c4cfe803ccf5\"")
             manifestPlaceholders.put("resizeable","false")
         }
}