安卓下载网络图片显示进度

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
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"
android:orientation="vertical"
>

<Button
android:id="@+id/download"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="DownLoadIMG"/>
<TextView
android:id="@+id/textview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="下载进度为"/>

<ProgressBar
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/progressBar" />

<ImageView
android:id="@+id/img"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />

</LinearLayout>

package com.baidu.downloadyellowimg;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

private Button mdownload;
private ProgressBar progressBar;
private ImageView mimageView;
private TextView textView;
private String imageUrl="这里放图片URL";
private Bitmap bitmap;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mdownload = (Button) findViewById(R.id.download);
progressBar = (ProgressBar) findViewById(R.id.progressBar);
mimageView = (ImageView) findViewById(R.id.img);
textView= (TextView) findViewById(R.id.textview);
mdownload.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Toast.makeText(getApplicationContext(), "开始下载文件", Toast.LENGTH_SHORT).show();
new DownLoadTask().execute(imageUrl);
}
});
}

class DownLoadTask extends AsyncTask<String,Integer,String>{

private long time;

@Override
protected void onPreExecute() {
super.onPreExecute();
time=0;
progressBar.setMax(100);
progressBar.setProgress(0);
textView.setText("开始下载");
mdownload.setEnabled(false);
//            这个方法是清理ImageView  释放内存
mimageView.setImageDrawable(new Drawable() {
@Override
public void draw(Canvas canvas) {

}

@Override
public void setAlpha(int i) {

}

@Override
public void setColorFilter(ColorFilter colorFilter) {

}

@Override
public int getOpacity() {
return 0;
}
});
if (bitmap!=null){
bitmap.recycle();
bitmap=null;
System.gc();
}
}

@Override
protected String doInBackground(String... urls) {
String imagePath=null;
URL url;
InputStream inputStream = null;
FileOutputStream fileOutputStream = null;
try {
//获取URL
url=new URL(urls[0]);
//开启连接
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
//设置超时的时间，5000毫秒即5秒
httpURLConnection.setConnectTimeout(5000);
//设置获取图片的方式为GET
httpURLConnection.setRequestMethod("GET");
//响应码为200，则访问成功
if (httpURLConnection.getResponseCode() == 200) {
//获取连接的输入流，这个输入流就是图片的输入流
inputStream = httpURLConnection.getInputStream();
//构建一个file对象用于存储图片
//这里我使用了一个生成目录的工具类，不清楚有没有可以直接生成文件目录的方法
String fileName=Util.getDefaultStoragePath(MainActivity.this)+File.separator+ System.currentTimeMillis()+".jpg";
File file = new File(fileName);
//获取输出流
fileOutputStream = new FileOutputStream(file);
//图片总共的长度
int total=httpURLConnection.getContentLength();
Log.e("xxxx","total:"+total);
//当前下载的长度
int length;
int length_count=0;
byte[] buffer = new byte[1024];
//将输入流写入到我们定义好的文件中
while ((length = inputStream.read(buffer)) != -1) {
fileOutputStream.write(buffer, 0, length);
length_count=length_count+length;
Log.e("xxxx","length_count:"+length_count);
int progress= (int)((float)length_count/total*100);
publishProgress(progress);
}
//将缓冲刷入文件
fileOutputStream.flush();
imagePath=file.getAbsolutePath();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//在最后，将各种流关闭
try {
if (inputStream != null) {
inputStream.close();
}
if (fileOutputStream != null) {
fileOutputStream.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
return imagePath;
}

@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
mdownload.setEnabled(true);
if (s==null){
textView.setText("下載失败");
return;
}
bitmap= BitmapFactory.decodeFile(s);
mimageView.setImageBitmap(bitmap);
textView.setText("下載完成");
//            下载完成置为100
progressBar.setProgress(100);
}

@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
//            保持两次更新时差500ms
if ((System.currentTimeMillis()-time)>500){
progressBar.setProgress(values[0]);
textView.setText("已下载 "+ values[0]+"%");
time=System.currentTimeMillis();
}
}
}

}