android-使用AsyncTask做下载进度条

效果：

代码：

package com.example.android_asynctask_download2;

import android.support.v7.app.ActionBarActivity;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends ActionBarActivity {
	private Button button;
	private ImageView imageView;
	private ProgressDialog dialog;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		button = (Button) this.findViewById(R.id.button1);
		imageView = (ImageView) this.findViewById(R.id.imageView1);
		dialog = new ProgressDialog(MainActivity.this);
		dialog.setCancelable(false);// 让dialog不能失去焦点，一直在最上层显示
		button.setOnClickListener(new View.OnClickListener() {
			@Override
			public void onClick(View v) {
				// 执行异步任务的操作
				new MyAsynTask().execute(
						"http://c.hiphotos.baidu.com/zhidao/pic/item/730e0cf3d7ca7bcb48f80cb9bc096b63f724a8a1.jpg");
			}
		});
	}

	/**
	 * 使用异步任务的规则： 1、生命一个集成AsyncTask标注三个参数的类型 2、第一个参数标识要执行的任务通常是网络的路径
	 * 3、第二个参数表示进度的刻度 4、第三个参数表示任务执行的结果
	 */
	public class MyAsynTask extends AsyncTask {

		// 表示任务执行之前的操作
		@Override
		protected void onPreExecute() {
			super.onPreExecute();
			dialog.setTitle("进度条");
			dialog.setMessage("正在加载图片,请稍后...");
			dialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
			dialog.show();
		}

		// 主要完成耗时操作
		@Override
		protected Bitmap doInBackground(String... params) {
			Bitmap bitmap = null;
			InputStream inputStream = null; 
			try {
				URL url = new URL(params[0]);
				HttpURLConnection connection = (HttpURLConnection) url.openConnection();
				connection.setConnectTimeout(3000);
				connection.setRequestMethod("GET");
				connection.setDoInput(true);
				ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
				if (connection.getResponseCode() == 200) {
					int file_length = connection.getContentLength();
					inputStream = connection.getInputStream();
					int len = 0;
					byte[] data = new byte[1024];
					int total_length = 0;
					while ((len = inputStream.read(data)) != -1) {
						total_length += len;
						outputStream.write(data, 0, len);
						int value = (int) ((total_length / (float) file_length) * 100);
						publishProgress(value);// 通过publishProgress将进度传递到onProgressUpdate中对进度更新
					}
					bitmap = BitmapFactory.decodeByteArray(outputStream.toByteArray(), 0, outputStream.size());
				}
			} catch (Exception e) {
				e.printStackTrace();
			}finally
			{
				if(inputStream!=null)
					try {
						inputStream.close();
					} catch (IOException e) {
						e.printStackTrace();
					}
			}
			return bitmap;
		}

		// 更新进度条操作
		@Override
		protected void onProgressUpdate(Integer... values) {
			super.onProgressUpdate(values);
			dialog.setProgress(values[0]);
		}

		// 主要更新UI操作
		@Override
		protected void onPostExecute(Bitmap result) {
			super.onPostExecute(result);
			imageView.setImageBitmap(result);
			dialog.dismiss();
		}

	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
}