设置状态栏透明

方法一：通过修改主题来设置状态栏变透明，需要在values、values-v19、values-v21目录下分别创建相应的主题。

//values
<style name="TranslucentTheme" parent="AppTheme">
</style>

//values-v19
<style name="TranslucentTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <item name="android:windowTranslucentStatus">true</item>
        <item name="android:windowTranslucentNavigation">false</item>
</style>

//values-v21
<style name="TranslucentTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <item name="android:windowTranslucentStatus">true</item>
        <item name="android:windowTranslucentNavigation">false</item>
        <item name="android:statusBarColor">@android:color/transparent</item>
</style>

   <style name="Theme.AppCompat.Light.NoActionBar">
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
    </style>

 方法二： 通过代码设置

    private void setStatusBarTransparent() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {//5.0及以上
            View decorView = getWindow().getDecorView();
            int option = View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                    | View.SYSTEM_UI_FLAG_LAYOUT_STABLE;
            decorView.setSystemUiVisibility(option);
            getWindow().setStatusBarColor(Color.TRANSPARENT);
        } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {//4.4到5.0
            WindowManager.LayoutParams localLayoutParams = getWindow().getAttributes();
            localLayoutParams.flags = (WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS | localLayoutParams.flags);
        }
    }

参考: 

Android 状态栏着色实践