public class MainActivity extends AppCompatActivity {

    private int p=0;//当前进度

    private ProgressBar pb_main_download;//进度条

    private TextView tv_main_desc;//显示文本的控件

    private MyHandler myHandler=new MyHandler();//新写的Handler类

    public class MyHandler extends Handler{

        @Override

        public void handleMessage(Message msg) {

            super.handleMessage(msg);

            int code=msg.what;//接受处理码

            switch (code){

                case 1:

                    p++;

                    pb_main_download.setProgress(p);//给进度条的当前进度赋值

                    tv_main_desc.setText(p+"%");//显示当前进度为多少

                    break;

            }

        }

    }

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        //根据ID找到进度条

        pb_main_download=findViewById(R.id.pb_main_download);

        //根据ID找到显示文本的控件

        tv_main_desc=findViewById(R.id.tv_main_desc);

    }

    //点击Download按钮所调用的方法

    public void download(View view) {

        if(0==p){//如果当前进度为0

            new myThread().start();//开启线程

        }

    }

    public class myThread extends Thread{

        @Override

        public void run() {

            super.run();

            while(true){

                try {

                    Thread.sleep(100);//使线程休眠0.1秒

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

                if(p==100){//当前进度等于总进度时退出循环

                    p=0;

                    break;

                }

                Message msg=new Message();

                msg.what=1;

                myHandler.sendMessage(msg);//发送处理码

            }

        }

    }

}