启动闪屏可以使用第三方库flutter_native_splash，但是启动界面中的黑色大状态栏太碍眼了

解决碍眼：
1、修改主题：
    <style name="LaunchTheme" parent="@android:style/Theme.Translucent.NoTitleBar">
        <!-- Show a splash screen on the activity. Automatically removed when
             Flutter draws its first frame -->
        <item name="android:windowBackground">@drawable/launch_background</item>

    </style>

2、修改launch_background.xml文件（v21也要改）
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<!--    <item>-->
<!--        <bitmap android:gravity="fill" android:src="@drawable/background"/>-->
<!--    </item>-->
    <item>
        <bitmap
            android:gravity="fill"
            android:scaleType="fitXY"
            android:src="@drawable/splash"
            />
    </item>
</layer-list>

3、修改MainActivity

class MainActivity : FlutterActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState);
        statusBarHide(this);
    }

    /**
     * 设置Activity的statusBar隐藏
     * @param activity
     */
    fun statusBarHide(activity: Activity) {
        // 代表 5.0 及以上
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            val decorView: View = activity.window.decorView
            val option: Int = View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
            decorView.setSystemUiVisibility(option)
            activity.window.statusBarColor = Color.parseColor("#A5D7F9");
            val actionBar = activity.actionBar
            actionBar.let {
                it?.let {
                    it.hide();
                }
            }
            return
        }

        // versionCode > 4.4  and versionCode < 5.0
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT && Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
            activity.window.addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS)
        }
    }


}

4、修改main.dart文件
void main() {
  setOverlayStyle();
  runApp(const MyApp());

}

//沉浸式状态栏
void setOverlayStyle(){
  //沉浸式状态栏
  if(Platform.isAndroid) {
    SystemChrome.setSystemUIOverlayStyle(
        SystemUiOverlayStyle(statusBarColor: Colors.transparent));
  }
}