package com.example.android_rogressbar;
import android.os.Handler;
import android.os.Message;
import android.os.StrictMode;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
  private ProgressBar pb_progress_bar;
  private TextView tv_main_text;
  private ImageView iv_main_image;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //根据ID获取控件
    pb_progress_bar = (ProgressBar) findViewById(R.id.pb_progress_bar);
    tv_main_text = (TextView) findViewById(R.id.tv_main_text);
  }
  //下载的方法
  public void download(View view){
    //启动线程
    new MyThread().start();
  }
  Handler handler=new Handler(){
    //接收消息，用于更新UI界面
    @Override
    public void handleMessage(Message msg) {
      super.handleMessage(msg);
      int i=msg.what;
      tv_main_text.setText(i+"");
    }
  };
  class MyThread extends Thread{
    @Override
    public void run() {
      super.run();
      for (int i = 0; i <= 100; i++) {
        pb_progress_bar.setProgress(i);
        //在子线程中发送消息
        handler.sendEmptyMessage(i);
        try {
          Thread.sleep(100);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
      }
    }
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:orientation="vertical"
  xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context="com.example.android_rogressbar.MainActivity">
  <!--style:设置进度条的样式，这里为直线进度条-->
  <ProgressBar
    style="?android:attr/progressBarStyleHorizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/pb_progress_bar"
    />
  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/tv_main_text"
    />
  <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="下载"
    android:onClick="download"
    />
</LinearLayout>