Android学习笔记之AsyncTask实现文件下载任务
来源：程序员人生 发布时间：2015-01-21 08:43:56 阅读次数：3249次
（1）该文件下载主要演示异步任务下载图片
（2）布局代码以下：1个ImageView用于寄存下载的图片，Button用于开始异步任务下载
<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" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginLeft="141dp"
android:layout_marginTop="135dp" />
<Button
android:id="@+id/button1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignRight="@+id/imageView1"
android:layout_marginBottom="80dp"
android:text="网页下载图片" />
</RelativeLayout>
（3）控制类
package com.example.asynctask_download;
import java.io.IOException;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import android.app.Activity;
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.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
public class MainActivity extends Activity {
private Button button1;
private ImageView imageView1;
private final String IMAGE_PATH = "http://www.baidu.com/img/bd_logo1.png";// 设置网页图片的地址
private ProgressDialog progressDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button1 = (Button) this.findViewById(R.id.button1);
imageView1 = (ImageView) this.findViewById(R.id.imageView1);
/*
* 下载进度条的设置
*/
progressDialog = new ProgressDialog(this);
progressDialog.setTitle("提示");
progressDialog.setCancelable(false);
progressDialog.setMessage("正在下载图片，请耐心等候！");
button1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
/*
* 异步任务、履行下载图片
*/
new MyTask().execute(IMAGE_PATH);
}
});
}
/*
* 异步任务：3个参数、4个步骤onPreExecute()、
* doInBackground()、onProgressUpdate（）、onPostExecute（）、没有参数传传进去的时候可使用void
*/
public class MyTask extends AsyncTask<String, Integer, byte[]> {
/*
* onPreExecute()方法在后台操作开始前运行在UI线程上
*/
@Override
protected void onPreExecute() {
super.onPreExecute();
progressDialog.show();
}
/*
* doInBackground方法运行在后台并处理后台操作
*/
@Override
protected byte[] doInBackground(String... params) {
HttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(params[0]);
byte[] result = null;
try {
HttpResponse httpResponse = httpClient.execute(httpGet);
if (httpResponse.getStatusLine().getStatusCode() == 200) {
result = EntityUtils.toByteArray(httpResponse.getEntity());
}
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
httpClient.getConnectionManager().shutdown();
}
return result;
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
/*
* 1旦后台操作终了，onPostExecute()方法就会在UI线程中运行
*/
@Override
protected void onPostExecute(byte[] result) {
super.onPostExecute(result);
/*
* 将下载的bitmap放置在imagView中去
* result就是下载的图片
*/
Bitmap bitmap = BitmapFactory.decodeByteArray(result, 0,
result.length);
imageView1.setImageBitmap(bitmap);
progressDialog.dismiss();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
结果：
（5）显示带刻度条的文件下载：
package com.example.asynctask_download;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import android.R.integer;
import android.app.Activity;
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.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
public class MainActivity extends Activity {
private Button button1;
private ImageView imageView1;
private final String IMAGE_PATH = "http://img.daimg.com/uploads/allimg/150114/3⑴50114151438.jpg";// 设置网页图片的地址
private ProgressDialog progressDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button1 = (Button) this.findViewById(R.id.button1);
imageView1 = (ImageView) this.findViewById(R.id.imageView1);
/*
* 下载进度条的设置
*/
progressDialog = new ProgressDialog(this);
progressDialog.setTitle("提示");
progressDialog.setCancelable(false);
progressDialog.setMessage("正在下载图片，请耐心等候！");
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
button1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
/*
* 异步任务、履行下载图片
*/
new MyTask().execute(IMAGE_PATH);
}
});
}
/*
* 异步任务：3个参数：第1个地址、第2个、第3个结果 4个步骤：onPreExecute()、
* doInBackground()、onProgressUpdate（）、onPostExecute（）、没有参数传传进去的时候可使用void
*/
public class MyTask extends AsyncTask<String, Integer, byte[]> {
/*
* onPreExecute()方法在后台操作开始前运行在UI线程上
*/
@Override
protected void onPreExecute() {
super.onPreExecute();
progressDialog.show();
}
/*
* doInBackground方法运行在后台并处理后台操作
*/
@Override
protected byte[] doInBackground(String... params) {
HttpClient httpClient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(params[0]); // 第1个参数即是传入的文件地址
byte[] result = null;
InputStream inputStream = null; // 文件流
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
try {
HttpResponse httpResponse = httpClient.execute(httpGet);
long file_length = httpResponse.getEntity().getContentLength();// 文件总长度
int total_length = 0;
byte[] data = new byte[1024];
int len = 0;
if (httpResponse.getStatusLine().getStatusCode() == 200) {
// result =
// EntityUtils.toByteArray(httpResponse.getEntity());
inputStream = httpResponse.getEntity().getContent();
while ((len = inputStream.read(data)) != ⑴) {
total_length += len;
// 产生刻度，进度
int progress_value = (int) ((total_length / (float) file_length) * 100);
publishProgress(progress_value); // 发布刻度单位
outputStream.write(data, 0, len);
}
}
result = outputStream.toByteArray();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
httpClient.getConnectionManager().shutdown();
}
return result;
}
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
progressDialog.setProgress(values[0]);
}
/*
* 1旦后台操作终了，onPostExecute()方法就会在UI线程中运行
*/
@Override
protected void onPostExecute(byte[] result) {
super.onPostExecute(result);
/*
* 将下载的bitmap放置在imagView中去 result就是下载的图片
*/
Bitmap bitmap = BitmapFactory.decodeByteArray(result, 0,
result.length);
imageView1.setImageBitmap(bitmap);
progressDialog.dismiss();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
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