android 创建子线程来执行耗时操作 友好提示加载中，然后显示UI

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:layout_gravity="center"
        android:orientation="horizontal"
        android:id="@+id/ll_loading">
        <com.google.android.material.progressindicator.CircularProgressIndicator
            android:id="@+id/chat_item_progress"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:indeterminate="true"
            android:visibility="visible"
            app:indicatorColor="@array/custom_progress_colors"
            app:indicatorSize="@dimen/space_25" />
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/load_waiting"/>
    </LinearLayout>

</FrameLayout>

class threadClass extends Thread {

    @Override
    public void run() {
        super.run();
        try{
            ....
        }catch(Exception ex){
            ...
　　　　 }
        handler.sendEmptyMessage(0);
    } 
}

Handler handler = new Handler(Looper.myLooper()) {
    @Override
    public void dispatchMessage(@NonNull Message msg) {
        super.dispatchMessage(msg);
        //更新ui
    }
}

new threadClass().start();