AsyncTask的使用

MainActivity 

package com.example.threadlean;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.ProgressBar;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

public class MainActivity extends AppCompatActivity {
    private TextView show;
    private ProgressBar progressBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        show = findViewById(R.id.show);
        progressBar = findViewById(R.id.pro);
    }

    public void download(View view) throws MalformedURLException {
        DownTask task = new DownTask(this, progressBar);
        task.execute(new URL("http://www.crazyit.org/index.php"));
    }

    //1.输入参数类型
    //2.进度类型
    //3.完成后返回值类型
    class DownTask extends AsyncTask {
        private ProgressBar progressBar;
        //定义记录已经读取的行数
        int hasRead = 0;
        Context mContext;

        public DownTask(Context context, ProgressBar progressBar) {
            this.mContext = context;
            this.progressBar = progressBar;
        }

        //线程将要完成的任务
        @Override
        protected String doInBackground(URL... urls) {
            StringBuilder sb = new StringBuilder();
            try {
                URLConnection urlConnection = urls[0].openConnection();
                BufferedReader br = new BufferedReader(new InputStreamReader(urlConnection.getInputStream(), "utf-8"));
                String line = null;
                while ((line = br.readLine()) != null) {
                    sb.append(line + "\n");
                    hasRead++;
                    //返回进度
                    publishProgress(hasRead);
                }
                return sb.toString();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }

        //线程完成后调用返回doInBackground的结果
        @Override
        protected void onPostExecute(String s) {
            show.setText(s);
            progressBar.setVisibility(View.INVISIBLE);
        }

        //doInBackground之前执行
        @Override
        protected void onPreExecute() {
            progressBar.setVisibility(View.VISIBLE);
            progressBar.setProgress(0);
            progressBar.setMax(120);
        }

        //当doInBackground()->publishProgress()执行后触发
        @Override
        protected void onProgressUpdate(Integer... values) {
            show.setText("读取" + values[0] + "行");
            progressBar.setProgress(values[0]);
        }
    }
}

activity_main.xml