（1）

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    tools:context=".MainActivity" >

    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="进度条的使用：" />

    <ProgressBar

        android:id="@+id/progressBar1"

        style="?android:attr/progressBarStyleHorizontal"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignLeft="@+id/button1"

        android:layout_alignRight="@+id/button1"

        android:layout_below="@+id/textView1"

        android:layout_marginTop="30dp" />

    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignLeft="@+id/textView1"

        android:layout_below="@+id/progressBar1"

        android:layout_marginLeft="74dp"

        android:layout_marginTop="146dp"

        android:text="下载图片" />

</RelativeLayout>

（2）

package com.example.progressbar;

import android.app.Activity;

import android.os.AsyncTask;

import android.os.Bundle;

import android.view.Menu;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.ProgressBar;

public class MainActivity extends Activity {

	private Button button1;

	private ProgressBar progressBar1;

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		setContentView(R.layout.activity_main);

		button1 = (Button) this.findViewById(R.id.button1);

		progressBar1 = (ProgressBar) this.findViewById(R.id.progressBar1);

		progressBar1.setMax(100);// 设置最大值为100

		button1.setOnClickListener(new OnClickListener() {

			@Override

			public void onClick(View v) {

				new MyTask().execute();

			}

		});

	}

	class MyTask extends AsyncTask<Void, Integer, Void> {

		@Override

		protected void onProgressUpdate(Integer... values) {

			super.onProgressUpdate(values);

			progressBar1.setProgress(values[0]);

		}

		@Override

		protected Void doInBackground(Void... params) {

			int i = 1;

			while (i <= 100) {

				try {

					Thread.sleep(500);

				} catch (Exception e) {

					// TODO: handle exception

				}

				publishProgress(i);

				i++;

			}

			return null;

		}

	}

	@Override

	public boolean onCreateOptionsMenu(Menu menu) {

		// Inflate the menu; this adds items to the action bar if it is present.

		getMenuInflater().inflate(R.menu.main, menu);

		return true;

	}

}

（3）演示效果

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