activity_logined.xml ui页面

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ProgressBar
        android:id="@+id/pb"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
        android:max="100"
        android:min="0"/>
</LinearLayout>

public class LoginedActivity extends AppCompatActivity {
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_logined);
        MyTask myTask = new MyTask();
        myTask.execute();//执行异步任务
    }

    /* 使用AsyncTask模拟下载事件进度条*/
    class MyTask extends AsyncTask<Void, Integer, String> {
        ProgressBar progressBar;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected String doInBackground(Void... voids) {//仅此方法加载在子线程中
            progressBar = findViewById(R.id.pb);
            for (int i = 0; i < 100; i++) {
                try {
                    Thread.sleep(100);
                    onProgressUpdate(i + 1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            return "加载成功";
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
            progressBar.setProgress(values[0]);
        }

        @Override
        protected void onPostExecute(String s) { //耗时操作结束回调方法
            super.onPostExecute(s);
            progressBar.setVisibility(View.GONE);
            Toast.makeText(LoginedActivity.this, s, Toast.LENGTH_SHORT).show();
        }
    }


}

AsyncTask封装了handler与Thread，更新ui页面只能在主线程中
使用handler与Thread方式较为麻烦，此处仅演示一次消息传送过程

public class MainActivity extends AppCompatActivity {
    Button btn;
    
    Handler handler=new Handler(){
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            if(msg.what==101){
                String message= (String) msg.obj;//类型强制转换
                btn.setText(message);
            }
        }
    };
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn=findViewById(R.id.btn);

        /*线程更改ui的使用 通过Handler*/
        new Thread(){
            @Override
            public void run() {
                super.run();
                try {
                    Thread.sleep(10000);
                    Message message=new Message();
                    message.what=101;
                    message.obj="我是消息";
                    handler.sendMessage(message);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();