WP_图片管理机制/异步读取网络图片

首页 > 代码库 > WP_图片管理机制/异步读取网络图片

WP_图片管理机制/异步读取网络图片

2024-07-17 20:48:50 222人阅读

项目有这样的需求,

要求窗口加载一揽子图片,为了不让UI阻塞太久,采用异步读取后绑定显示的方案.

图片的下载应该采用并发的过程(等待网络响应会很耗时,一张一张的下载,等待时间太长)

图片的下载不能占用过多的线程数,应有个阀值(图片不是核心业务,不能占用那么多资源)

在图片加载的过程中,如果用户有操作,比如窗口跳转,则未加载完成的图片加载的过程应取消(为了替用户节省流量).

需求就是这么多了,如何实现呢?

思路是这样的,由于需要异步,且需要等待,首先想到使用队列,先让队列排列起来,再定量迭代读取.

因为要涉及异步的取消,想到了用WebClient对象的异步功能, 当然,所以发起异步请求之后的对象我都需要记录,

所以还需要一个list容器.

外部接口是两个参数,url,图片的网址,一个回调,定义了图片下载完成后的操作.

内部的核心流程,

1.将一个图片任务从队列中取出,

2.异步发生此请求,

3.将发起请求的对象放进容器,以备撤销时使用.

撤销的核心流程是.

1.让处理线程停止

2.取消队列中的任务,

3.让等待响应的任务取消.

using System;

using System.Windows;

using System.Windows.Media.Imaging;

using Proj.Interface;

namespace Proj.Common

    /// <summary>

    /// 把网络数据包装为图片源

    /// </summary>

    public class HttpPicGet : IRevocable

        public event GetPicCallback OnImageLoadCompleted;

        public event Action ProcessCompleted;

        /// <summary>

        /// 当前正在处理的URL

        /// </summary>

        public string Url;

        HttpResourceGet m_httpGet;

        public HttpPicGet()

            m_httpGet = new HttpResourceGet();

            m_httpGet.OnDataStreamGenerated += (stream =>

                Deployment.Current.Dispatcher.BeginInvoke(() =>

                    BitmapSource bi = new BitmapImage();

                    bi.SetSource(stream);

                    if (OnImageLoadCompleted != null)

                        OnImageLoadCompleted(bi);

});

});

            m_httpGet.ProcessCompleted += (() =>

                //Deployment.Current.Dispatcher.BeginInvoke(() =>

                // {

                     if (ProcessCompleted != null)

                         ProcessCompleted();

                 //});

});

        public void BeginLoadPic(string url)

            Url = url;

            m_httpGet.BeginGetData(url);

        public void RevokeAsync()

            m_httpGet.RevokeAsync();

using System;

using System.IO;

using System.Net;

using System.Windows.Media.Imaging;

using Proj.Interface;

namespace Proj.Common

    /// <summary>

    /// 从网络读取流的回调

    /// </summary>

    public delegate void GetDataStreamCallback(Stream stream);

    /// <summary>

    /// 生成了图片源之后的回调

    /// </summary>

    public delegate void GetPicCallback(BitmapSource bimage);

    /// <summary>

    /// 获取网络数据

    /// </summary>

    public class HttpResourceGet : IRevocable

        public event GetDataStreamCallback OnDataStreamGenerated;

        public event Action ProcessCompleted;

        WebClient m_client;

        public HttpResourceGet()

            m_client = new WebClient();

            m_client.OpenReadCompleted += ((send, ev) =>

do

                    if (ev.Error != null || ev.Cancelled)

                        break;

                    if (OnDataStreamGenerated != null)

                        OnDataStreamGenerated(ev.Result);

                        //ev.Result.Close();

                } while (false);

                if (ProcessCompleted != null)

                    ProcessCompleted();

});

        public void BeginGetData(string url)

            if (url.Contains("?"))

                url += "&rand=" + Guid.NewGuid();//加Guid保证调试时无缓存

            else

                url += "?rand=" + Guid.NewGuid();//加Guid保证调试时无缓存

            m_client.OpenReadAsync(new Uri(url));

        public void RevokeAsync()

            m_client.CancelAsync();

using System.ComponentModel;

using System.Windows.Media.Imaging;

namespace Proj.Common

    public class MyImage : INotifyPropertyChanged

        public event PropertyChangedEventHandler PropertyChanged;

        string m_url;

        BitmapSource m_source;

        public string URL

            get { return m_url; }

set

                if (m_url != value)

                    m_url = value;

                    OnPropertyChanged(new PropertyChangedEventArgs("URL"));

        public BitmapSource Source

            get { return m_source; }

set

                if (m_source != value)

                    m_source = value;

                    OnPropertyChanged(new PropertyChangedEventArgs("Source"));

        protected virtual void OnPropertyChanged(PropertyChangedEventArgs args)

            if (PropertyChanged != null)

                PropertyChanged(this, args);

using System.Collections.Generic;

using System.ComponentModel;

using System.Threading;

using Proj.Interface;

namespace Proj.Common

    /// <summary>

    /// 容器,用来处理多条任务

    /// </summary>

    public class RevocableContainer

        private class QueueItem

            public GetPicCallback action;

            public string url;

        const int Threshold =3;

        AutoResetEvent m_event;

        int m_count;

        bool m_isThreadProcessing;

        Queue<QueueItem> m_queue;

        List<IRevocable> m_list;

        object m_lock;

        public RevocableContainer()

            m_event = new AutoResetEvent(false);

            m_queue = new Queue<QueueItem>();

            m_list = new List<IRevocable>();

            m_lock = new object();

            m_count = Threshold;

            m_isThreadProcessing = false;

        void HttpRequestThread()

            while (true)

                if (m_count == 0)

                    m_event.WaitOne();

                QueueItem item = null;

                //out from queue

                lock (m_queue)

                    if (!m_isThreadProcessing)

                        break;

                    if (m_queue.Count == 0)

                        break;

                    item = m_queue.Dequeue();

                    Interlocked.Decrement(ref  m_count);

                //do request

                HttpPicGet pic = new HttpPicGet();

                pic.OnImageLoadCompleted += (img =>

                    item.action(img);

});

                pic.ProcessCompleted += (() =>

                    lock (m_list)

                        m_list.Remove(pic);

                    if (m_count == 0)

                        m_event.Set();

                    Interlocked.Increment(ref m_count);

});

                pic.BeginLoadPic(item.url);

                //into list

                lock (m_list)

                    m_list.Add(pic);

                Thread.Sleep(1);

        public void EnQueue(string url, GetPicCallback action)

            QueueItem item = new QueueItem() { action = action, url = url };

            BackgroundWorker worker = null;

            lock (m_queue)

                m_queue.Enqueue(item);

                if (!m_isThreadProcessing)

                    m_isThreadProcessing = true;

                    worker = new BackgroundWorker();

            if (worker != null)

                worker.DoWork += ((send, ev) => HttpRequestThread());

                worker.RunWorkerCompleted += ((send, ev) =>

                    lock (m_queue)

                        m_isThreadProcessing = false;

});

                worker.RunWorkerAsync();

        /// <summary>

        /// 取消全部，并返回未完成的(正在进行的及未开始的)

        /// </summary>

        public List<string> CancelAll()

            List<string> unFinishedUrls=new List<string>();

            lock (m_queue)

                m_isThreadProcessing = false;

                if (m_queue.Count > 0)

                    foreach (var queueItem in m_queue)

                        unFinishedUrls.Add(queueItem.url);

                m_queue.Clear();

            lock (m_list)

                foreach (IRevocable item in m_list)

                    HttpPicGet picGet = (HttpPicGet)item;

                    unFinishedUrls.Add(picGet.Url);

                    item.RevokeAsync();

            return unFinishedUrls;

界面层：

using System;

using System.Collections.Generic;

using System.Linq;

using System.Windows;

using Proj.Common;

using Microsoft.Phone.Controls;

namespace Proj

    public partial class PageImgTest : PhoneApplicationPage

        RevocableContainer m_container = new RevocableContainer();

        List<string> _unFinishUrls = new List<string>();

        List<string> sources = new List<string>()

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526395.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526396.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526397.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526398.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526399.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526400.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526401.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526402.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526403.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526404.jpg",

                //"http://gb.cri.cn/mmsource/images/2008/05/26/ei080526405.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526406.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526407.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526408.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526409.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526410.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526411.jpg",

                "http://gb.cri.cn/mmsource/images/2008/05/26/ei080526412.jpg"

};

        // Constructor

        public PageImgTest()

            InitializeComponent();

        private void DoClick(object sender, RoutedEventArgs e)

            if (_unFinishUrls.Count > 0)

                StartLoad(_unFinishUrls);

            else

                StartLoad(sources);

        private void RevokeClick(object sender, RoutedEventArgs e)

            _unFinishUrls = m_container.CancelAll();

            MessageBox.Show("未完成数：" + _unFinishUrls.Count);

        private void BtnRetry_OnClick(object sender, RoutedEventArgs e)

            if (!_isInit || lbContent.Items.Count == 0) return;

            //将未完成的图片继续加载

            StartLoad(_unFinishUrls);

        private bool _isInit = false;

        /// <summary>

        /// 加载/继续加载未完成的

        /// </summary>

        void StartLoad(List<string> argImgUrls)

            if (argImgUrls == null || argImgUrls.Count == 0) return;

            List<MyImage> imgs = new List<MyImage>();

            //MyImage[] imgs = new MyImage[sources.Count];

            //for (int i = 0; i < argImgUrls.Count; ++i)

//{

            //    MyImage imgItem = new MyImage();

            //    imgs.Add(imgItem);

            //    //imgs[i] = new MyImage();

            //    //MyImage imgItem = imgs[i];

            //    imgItem.URL = sources[i] + "?rand=" + Guid.NewGuid().ToString();//加Guid保证调试时无缓存

            //    m_container.EnQueue(imgItem.URL, (bitsource => imgItem.Source = bitsource));

//}

            if (!_isInit)

                for (int i = 0; i < argImgUrls.Count; ++i)

                    MyImage imgItem = new MyImage();

                    imgs.Add(imgItem);

                    imgItem.URL = sources[i];

                    m_container.EnQueue(imgItem.URL, (bitsource => imgItem.Source = bitsource));

                lbContent.DataContext = imgs;

            else

                for (int i = 0; i < argImgUrls.Count; ++i)

                    MyImage imgItem = new MyImage();

                    imgs.Add(imgItem);

                    imgItem.URL = argImgUrls[i];

                    m_container.EnQueue(imgItem.URL, (bitsource => imgItem.Source = bitsource));

                for (int i = 0; i < lbContent.Items.Count; i++)

                    MyImage myImg = (MyImage)lbContent.Items[i];

                    var item = (from c in argImgUrls where c == myImg.URL select c).FirstOrDefault();

                    if (!string.IsNullOrEmpty(item))//匹配上

                        m_container.EnQueue(item, (bitsource => myImg.Source = bitsource));

            if (!_isInit && imgs.Count > 0)

                _isInit = true;

                UpdateLayout();

<phone:PhoneApplicationPage

    x:Class="Proj.PageImgTest"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"

    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

    FontFamily="{StaticResource PhoneFontFamilyNormal}"

    FontSize="{StaticResource PhoneFontSizeNormal}"

    Foreground="{StaticResource PhoneForegroundBrush}"

    SupportedOrientations="Portrait" Orientation="Portrait"

    mc:Ignorable="d"

    shell:SystemTray.IsVisible="True">

    <!--LayoutRoot is the root grid where all page content is placed-->

    <Grid x:Name="LayoutRoot" Background="Transparent">

        <Grid.RowDefinitions>

            <RowDefinition Height="Auto"/>

            <RowDefinition Height="*"/>

        </Grid.RowDefinitions>

        <ListBox Height="670" x:Name="lbContent" Grid.Row="0" ItemsSource="{Binding}">

            <ListBox.ItemTemplate>

                <DataTemplate>

                    <StackPanel Orientation="Horizontal">

                        <Image Height="100" Width="100" Source="{Binding Source, Mode=OneWay}" />

                        <TextBlock Text="{Binding URL}" />

                    </StackPanel>

                </DataTemplate>

            </ListBox.ItemTemplate>

        </ListBox>

        <!--ContentPanel - place additional content here-->

        <Grid x:Name="ContentPanel" Grid.Row="1" VerticalAlignment="Bottom" Margin="12,0,12,0">

            <StackPanel Orientation="Horizontal">

                <Button x:Name="btnDo" Width="100" Height="100" Content="DO" Click="DoClick" />

                <Button x:Name="btnRevoke" Width="100" Height="100" Content="Revoke" Click="RevokeClick"  />

                <Button x:Name="btnRetry" Width="120" Height="100" Content="Retry" Click="BtnRetry_OnClick" />

            </StackPanel>

        </Grid>

    </Grid>

</phone:PhoneApplicationPage>

参考地址：http://blog.csdn.net/antsnm/article/details/6738292

声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉：投诉/举报工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。

联系
我们

首页 > 代码库 > WP_图片管理机制/异步读取网络图片

WP_图片管理机制/异步读取网络图片

看完仍有疑问？有类似问题直接问程序猿