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为什么在下载图像时progressBar永远不会达到100％并且我超出范围异常？

[英]Why when downloading images the progressBar never get to 100% and i'm getting out of range exception?

 原文  2016-12-29 06:42:04  9   2    c#/ .net/ winforms

问题描述

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using System.Net;
using System.Threading;

namespace SatelliteImages
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            ExtractImages ei = new ExtractImages();
            ei.Init();

            progressBar1.Minimum = 0;
            progressBar1.Maximum = 100;

            backgroundWorker1.RunWorkerAsync();
        }



        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {

        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker worker = sender as BackgroundWorker;

            for (int i = 0; i <= ExtractImages.imagesUrls.Count(); i++)
            {
                if (worker.CancellationPending == true)
                {
                    e.Cancel = true;
                    break;
                }
                else
                {
                    using (var client = new WebClient())
                    {
                        client.DownloadFile(ExtractImages.imagesUrls[i], @"C:\Temp\TestingSatelliteImagesDownload\" + i + ".jpg");
                        worker.ReportProgress(100 * i / ExtractImages.imagesUrls.Count());
                    }
                }
            }
        }

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
            label2.Text = (e.ProgressPercentage.ToString() + "%");
        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Error == null)
            {
                MessageBox.Show("Completed without any errors");
            }
            else
            {
                string myerr = e.Error.ToString();
            }
        }
    }
}

  1. 为什么progressBar1达到99％并停在那里，然后到达完成的事件？ 我怎样才能达到100％？

  2. 我计算reportProgress的方式和从i = 0开始的FOR循环是否正常？

  3. 如何在表单上显示新标签（例如label3）并显示剩余文件下载数量？ 例如，如果在imagesUrls中有399个项目（要下载的文件），则在label3中，我希望看到每次下载文件并成功将其从399改为0或1的计数器。

  4. 现在到完成的事件时，我得到了例外：

e.Error = {“索引超出范围。必须为非负数，并且小于集合的大小。\\ r \\ n参数名称：index”}

D：\\ C-Sharp \\中的Satellite.Images.Form1.backgroundWorker1_DoWork（Object sender，DoWorkEventArgs e）的System.Collections.Generic.List`1.get_Item（Int32 index）处的System.ThrowHelper.ThrowArgumentOutOfRangeException（ExceptionArgument参数，ExceptionResource资源）中在System.ComponentModel.BackgroundWorker.OnDoWork（DoWorkEventArgs e）处的SatelliteImages \\ SatelliteImages \\ SatelliteImages \\ Form1.cs：第60行
在System.ComponentModel.BackgroundWorker.WorkerThreadStart（Object参数）

我尝试的更新： 

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using System.Net;
using System.Threading;

namespace SatelliteImages
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            ExtractImages ei = new ExtractImages();
            ei.Init();
        }



        private async void Form1_Load(object sender, EventArgs e)
        {
            label1.Text = "0 %";
            progressBar1.Minimum = 0;
            progressBar1.Maximum = ExtractImages.imagesUrls.Count() - 1;
            await DoWork();
        }

        private async Task DoWork()
        {
            for (int i = 0; i < ExtractImages.imagesUrls.Count(); i++)
            {
                using (var client = new WebClient())
                {
                    await client.DownloadFileTaskAsync(ExtractImages.imagesUrls[i], @"C:\Temp\TestingSatelliteImagesDownload\" + i + ".jpg");

                    progressBar1.Value = i + 1;
                    double average = (double)(i + 1) / ExtractImages.imagesUrls.Count();
                    label1.Text = (Math.Round(average, 1) * 100).ToString() + " %";
                }
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {

        }
    }
}

  1. progressBar尚未结束，它在99％处停止，我认为是99％。

  2. label1最后显示100％，但progressBar尚未结束。

  3. 最后，我也得到了例外：

该行的Program.cs中是一个例外： 

Application.Run(new Form1());

附加信息：调用的目标已引发异常。 

System.Reflection.TargetInvocationException was unhandled
  HResult=-2146232828
  Message=Exception has been thrown by the target of an invocation.
  Source=mscorlib
  StackTrace:
       at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
       at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
       at System.Delegate.DynamicInvokeImpl(Object[] args)
       at System.Windows.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme)
       at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme)
       at System.Windows.Forms.Control.InvokeMarshaledCallbacks()
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at SatelliteImages.Program.Main() in D:\C-Sharp\SatelliteImages\SatelliteImages\SatelliteImages\Program.cs:line 19
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 
       HResult=-2146233086
       Message=Value of '399' is not valid for 'Value'. 'Value' should be between 'minimum' and 'maximum'.
Parameter name: Value
       ParamName=Value
       Source=System.Windows.Forms
       StackTrace:
            at System.Windows.Forms.ProgressBar.set_Value(Int32 value)
            at SatelliteImages.Form1.<DoWork>d__2.MoveNext() in D:\C-Sharp\SatelliteImages\SatelliteImages\SatelliteImages\Form1.cs:line 46
         --- End of stack trace from previous location where exception was thrown ---
            at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
            at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
            at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
            at SatelliteImages.Form1.<Form1_Load>d__1.MoveNext() in D:\C-Sharp\SatelliteImages\SatelliteImages\SatelliteImages\Form1.cs:line 35
         --- End of stack trace from previous location where exception was thrown ---
            at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.<ThrowAsync>b__6_0(Object state)
       InnerException:

2 个解决方案

解决方案1
 1  2016-12-29 07:26:56

对于您的第一个，第二个和第四个问题：

您正在从0循环到两边都包括在内（0到<= count）。 这意味着您要循环计数+1次。 我不认为那是你的意图。 要解决此问题，建议您从i = 1开始。 我建议不要使用i = 0且i小于计数，因为根据您的计算，对于i = 0不会向进度栏添加任何进度。 尽管这些建议可能会有所帮助，但我强烈建议您设置progressbar.Maximum值进行计数，并在每次下载文件后仅将progressbar.Value递增1。

我怀疑您的计算是将除法结果舍入为整数。 因此，首先将i乘以100.0，然后执行除法。 像（i * 100.0）/（images_count）。

对于您的第三个要求：

请参考MSDN示例-https : //msdn.microsoft.com/zh-cn/library/t9fzsyec( v= vs.110).aspx

解决方案2
 1  2016-12-29 07:27:11

要解决你的答案，你需要更换<=与<在for循环。

现在您可以看到为什么async-await模式很有用，该代码像任何普通代码一样流动。 检查以下简单程序是否与您的相同： 

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private async void Form1_Load(Object sender, EventArgs e)
    {
        label1.Text = "0 %";
        progressBar1.Minimum = 0;
        progressBar1.Maximum = ExtractImages.imagesUrls.Count() - 1;
        await DoWork();
    }

    private async Task DoWork()
    {
        for (int i = 0; i < ExtractImages.imagesUrls.Count(); i++)
        {
            using (var client = new WebClient())
            {
                await client.DownloadFileTaskAsync(ExtractImages.imagesUrls[i], @"C:\Temp\TestingSatelliteImagesDownload\" + i + ".jpg");

                progressBar1.Value = i + 1;
                double average = (double)(i + 1) / ExtractImages.imagesUrls.Count();
                label1.Text = (Math.Round(average, 1) * 100).ToString() + " %";
            }
        }
    }
}

请注意，您可以使用IProgress<int>并将更新UI的代码与下载文件的代码解耦： 

private async void Form1_Load(Object sender, EventArgs e)
{
    label1.Text = "0 %";
    var progress = new Progress<int>();
    progress.ProgressChanged += Progress_ProgressChanged;
    await DoWork(progress);
}

private void Progress_ProgressChanged(Object sender, Int32 e)
{
     progressBar1.Value = e + 1;
     double average = ((double)(e + 1) / (ExtractImages.imagesUrls.Count()));
     label3.Text = (Math.Round(average, 1) * 100).ToString() + " %";
}

然后在下载文件之后添加： 

progress.Report(i);

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