为什么我的 C++/CLI 应用程序没有响应，即使我使用了 BackgroundWorker？

Question

我只是想学习一些 Windows 表单内容以供参考，使用 C++/CLI。我使用默认的 Windows Forms 选项在 VS 2010 中创建了一个名为 LibraryScan 的项目，并使用一些控件修改了表单。我所做的所有代码更改都在 Form1.h 中（见下文）。我添加了整个 Form1.h 因为我想如果你只是创建一个普通的 VS 2010 C++/CLI Windows Forms 应用程序你可以用下面的内容替换自动生成的 Form1.h （尽管需要考虑图像列表；项目 [0] 是通用文档图标，[1] 是关闭的文件夹，[2] 是打开的文件夹）。

基本上你使用"Browse..."按钮到select一个文件夹，然后按"Scan"按钮，目的是它会递归通过根文件夹及其子文件夹来查找里面的所有文件。每个文件的名称被添加到一个多行的TextBox 中，树结构在一个TreeView 中生成。

我遇到的问题是，没有这条线：

System::Threading::Thread::Sleep(1);

在 listFolder() 函数中，UI 在扫描文件夹时有点反应迟钝。 TextBox 更新正常，但 TreeView 直到扫描完成才显示，并且在扫描时，您无法调整应用程序大小或移动应用程序 window。 Sleep(1) 进去没问题，虽然有点慢！

正如我所说，我是 Windows Forms 的新手，但对 MFC 有一些经验（尽管我 27 年以上的软件开发经验中的大部分都是嵌入式的，所以..）包括使用事件泵来尝试解决这类问题。然而，到目前为止我所做的阅读似乎表明 BackgroundWorker class 和 RunWorkerAsync()/ReportProgress() 等是 C++/CLI/Windows 形式的方式，但大多数问题和示例都在C# 和我使用 BackgroundWorker 搜索无响应的 GUI 的所有结果都以我看不到的解决方案与我正在做的有很大不同！

感谢任何帮助。

#pragma once

ref class ProgressObject;

namespace LibraryScan {

    using namespace System;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;
    using namespace System::IO;

    /// <summary>
    /// Summary for Form1
    /// </summary>
    public ref class Form1 : public System::Windows::Forms::Form
    {
    public:
        Form1(void)
        {
            InitializeComponent();
            //
            //TODO: Add the constructor code here
            //
        }

    protected:
        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        ~Form1()
        {
            if (components)
            {
                delete components;
            }
        }
    private: System::Windows::Forms::Label^  label1;
    protected: 
    private: System::Windows::Forms::TextBox^  textBox1;
    private: System::Windows::Forms::Button^  button1;
    private: System::Windows::Forms::FolderBrowserDialog^  folderBrowserDialog1;
    private: System::Windows::Forms::OpenFileDialog^  openFileDialog1;
    private: System::Windows::Forms::TextBox^  textBoxFiles;
    private: System::Windows::Forms::Label^  label2;
    private: System::Windows::Forms::Button^  buttonScan;
    private: System::Windows::Forms::TreeView^  treeViewFiles;
    private: System::Windows::Forms::ImageList^  imageList1;
    private: System::ComponentModel::BackgroundWorker^  fileLister;
    private: System::ComponentModel::IContainer^  components;



    private:
        /// <summary>
        /// Required designer variable.
        /// </summary>


#pragma region Windows Form Designer generated code
        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        void InitializeComponent(void)
        {
            this->components = (gcnew System::ComponentModel::Container());
            System::ComponentModel::ComponentResourceManager^  resources = (gcnew System::ComponentModel::ComponentResourceManager(Form1::typeid));
            this->label1 = (gcnew System::Windows::Forms::Label());
            this->textBox1 = (gcnew System::Windows::Forms::TextBox());
            this->button1 = (gcnew System::Windows::Forms::Button());
            this->folderBrowserDialog1 = (gcnew System::Windows::Forms::FolderBrowserDialog());
            this->openFileDialog1 = (gcnew System::Windows::Forms::OpenFileDialog());
            this->textBoxFiles = (gcnew System::Windows::Forms::TextBox());
            this->label2 = (gcnew System::Windows::Forms::Label());
            this->buttonScan = (gcnew System::Windows::Forms::Button());
            this->treeViewFiles = (gcnew System::Windows::Forms::TreeView());
            this->imageList1 = (gcnew System::Windows::Forms::ImageList(this->components));
            this->fileLister = (gcnew System::ComponentModel::BackgroundWorker());
            this->SuspendLayout();
            // 
            // label1
            // 
            this->label1->AutoSize = true;
            this->label1->Location = System::Drawing::Point(28, 13);
            this->label1->Name = L"label1";
            this->label1->Size = System::Drawing::Size(39, 13);
            this->label1->TabIndex = 0;
            this->label1->Text = L"Folder:";
            // 
            // textBox1
            // 
            this->textBox1->Location = System::Drawing::Point(74, 13);
            this->textBox1->Name = L"textBox1";
            this->textBox1->Size = System::Drawing::Size(409, 20);
            this->textBox1->TabIndex = 1;
            // 
            // button1
            // 
            this->button1->Location = System::Drawing::Point(489, 13);
            this->button1->Name = L"button1";
            this->button1->Size = System::Drawing::Size(75, 23);
            this->button1->TabIndex = 2;
            this->button1->Text = L"Browse...";
            this->button1->UseVisualStyleBackColor = true;
            this->button1->Click += gcnew System::EventHandler(this, &Form1::button1_Click);
            // 
            // folderBrowserDialog1
            // 
            this->folderBrowserDialog1->Description = L"Select the directory that you want to scan.";
            this->folderBrowserDialog1->ShowNewFolderButton = false;
            // 
            // openFileDialog1
            // 
            this->openFileDialog1->FileName = L"openFileDialog1";
            // 
            // textBoxFiles
            // 
            this->textBoxFiles->Anchor = static_cast<System::Windows::Forms::AnchorStyles>(((System::Windows::Forms::AnchorStyles::Top | System::Windows::Forms::AnchorStyles::Bottom) 
                | System::Windows::Forms::AnchorStyles::Right));
            this->textBoxFiles->Location = System::Drawing::Point(34, 62);
            this->textBoxFiles->Multiline = true;
            this->textBoxFiles->Name = L"textBoxFiles";
            this->textBoxFiles->ScrollBars = System::Windows::Forms::ScrollBars::Both;
            this->textBoxFiles->Size = System::Drawing::Size(596, 419);
            this->textBoxFiles->TabIndex = 3;
            this->textBoxFiles->WordWrap = false;
            // 
            // label2
            // 
            this->label2->AutoSize = true;
            this->label2->Location = System::Drawing::Point(31, 43);
            this->label2->Name = L"label2";
            this->label2->Size = System::Drawing::Size(31, 13);
            this->label2->TabIndex = 4;
            this->label2->Text = L"Files:";
            // 
            // buttonScan
            // 
            this->buttonScan->Enabled = false;
            this->buttonScan->Location = System::Drawing::Point(570, 13);
            this->buttonScan->Name = L"buttonScan";
            this->buttonScan->Size = System::Drawing::Size(75, 23);
            this->buttonScan->TabIndex = 5;
            this->buttonScan->TabStop = false;
            this->buttonScan->Text = L"Scan";
            this->buttonScan->UseVisualStyleBackColor = true;
            this->buttonScan->Click += gcnew System::EventHandler(this, &Form1::buttonScan_Click);
            // 
            // treeViewFiles
            // 
            this->treeViewFiles->Anchor = static_cast<System::Windows::Forms::AnchorStyles>(((System::Windows::Forms::AnchorStyles::Top | System::Windows::Forms::AnchorStyles::Bottom) 
                | System::Windows::Forms::AnchorStyles::Right));
            this->treeViewFiles->ImageIndex = 0;
            this->treeViewFiles->ImageList = this->imageList1;
            this->treeViewFiles->Location = System::Drawing::Point(636, 62);
            this->treeViewFiles->Name = L"treeViewFiles";
            this->treeViewFiles->SelectedImageIndex = 0;
            this->treeViewFiles->Size = System::Drawing::Size(392, 419);
            this->treeViewFiles->TabIndex = 6;
            this->treeViewFiles->AfterCollapse += gcnew System::Windows::Forms::TreeViewEventHandler(this, &Form1::treeViewFiles_AfterCollapse);
            this->treeViewFiles->AfterExpand += gcnew System::Windows::Forms::TreeViewEventHandler(this, &Form1::treeViewFiles_AfterExpand);
            // 
            // imageList1
            // 
            this->imageList1->ImageStream = (cli::safe_cast<System::Windows::Forms::ImageListStreamer^  >(resources->GetObject(L"imageList1.ImageStream")));
            this->imageList1->TransparentColor = System::Drawing::Color::Transparent;
            this->imageList1->Images->SetKeyName(0, L"Generic_Document.png");
            this->imageList1->Images->SetKeyName(1, L"Folder_16x16.png");
            this->imageList1->Images->SetKeyName(2, L"FolderOpen_16x16_72.png");
            // 
            // fileLister
            // 
            this->fileLister->WorkerReportsProgress = true;
            this->fileLister->DoWork += gcnew System::ComponentModel::DoWorkEventHandler(this, &Form1::fileLister_DoWork);
            this->fileLister->ProgressChanged += gcnew System::ComponentModel::ProgressChangedEventHandler(this, &Form1::fileLister_ProgressChanged);
            this->fileLister->RunWorkerCompleted += gcnew System::ComponentModel::RunWorkerCompletedEventHandler(this, &Form1::fileLister_RunWorkerCompleted);
            // 
            // Form1
            // 
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(1040, 493);
            this->Controls->Add(this->treeViewFiles);
            this->Controls->Add(this->buttonScan);
            this->Controls->Add(this->label2);
            this->Controls->Add(this->textBoxFiles);
            this->Controls->Add(this->button1);
            this->Controls->Add(this->textBox1);
            this->Controls->Add(this->label1);
            this->Name = L"Form1";
            this->Text = L"Form1";
            this->ResumeLayout(false);
            this->PerformLayout();

        }
#pragma endregion
    private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e)
             {
                 // Show the FolderBrowserDialog.
                 System::Windows::Forms::DialogResult result = folderBrowserDialog1->ShowDialog();
                 if ( result == System::Windows::Forms::DialogResult::OK )
                 {
                     String^ folderName = folderBrowserDialog1->SelectedPath;
                     textBox1->Text = folderName;
                     buttonScan->Enabled = true;
                 }
             }

    private: System::Void buttonScan_Click(System::Object^  sender, System::EventArgs^  e)
             {
                 // Scan the folder listed in textBox1 and add the files to textBoxFiles
                 String^ folder = textBox1->Text;
                 fileLister->RunWorkerAsync(folder);
             }

    private: long listFolder(String^ folderName, TreeNode^ rootNode, BackgroundWorker^ worker)
             {
                 // Scan the folder passed in and add the files to textBoxFiles
                 TreeNode^ newNode = gcnew TreeNode(folderName);
                 newNode->ImageIndex = 1;
                 newNode->SelectedImageIndex = 1;
                 worker->ReportProgress(0, gcnew ProgressObject(rootNode, newNode));

                 array<String^>^ file = Directory::GetFiles( folderName );
                 Array::Sort(file);
                 for (int i = 0; i < file->Length; i++)
                 {
                     TreeNode^ fileNode = gcnew TreeNode(file[i]);
                     worker->ReportProgress(0, gcnew ProgressObject(newNode, fileNode));
                     System::Threading::Thread::Sleep(1);
                 }

                 // Now scan the directories under this one
                 array<String^>^ dir = Directory::GetDirectories(folderName);
                 Array::Sort(dir);
                 for (int i = 0; i < dir->Length; i++)
                 {
                     listFolder(dir[i], newNode, worker);
                 }

                 return 0L;
             }

private: System::Void treeViewFiles_AfterCollapse(System::Object^  sender, System::Windows::Forms::TreeViewEventArgs^  e)
         {
             e->Node->ImageIndex = 1;
             e->Node->SelectedImageIndex = 1;
         }

private: System::Void treeViewFiles_AfterExpand(System::Object^  sender, System::Windows::Forms::TreeViewEventArgs^  e) 
         {
             e->Node->ImageIndex = 2;
             e->Node->SelectedImageIndex = 2;
         }
private: System::Void fileLister_DoWork(System::Object^  sender, System::ComponentModel::DoWorkEventArgs^  e)
         {
             BackgroundWorker^ worker = dynamic_cast<BackgroundWorker^>(sender);
             e->Result = listFolder(safe_cast<String^>(e->Argument), nullptr, worker);
         }
private: System::Void fileLister_ProgressChanged(System::Object^  sender, System::ComponentModel::ProgressChangedEventArgs^  e)
         {
             ProgressObject^ prog = safe_cast<ProgressObject^>(e->UserState);
             if (prog->currentNode != nullptr)
             {
                if (prog->rootNode == nullptr)
                {
                    treeViewFiles->Nodes->Add(prog->currentNode);
                }
                else
                {
                    prog->rootNode->Nodes->Add(prog->currentNode);
                }
                textBoxFiles->AppendText(String::Concat(prog->currentNode->Text, "\n"));
             }
         }

private: System::Void fileLister_RunWorkerCompleted(System::Object^  sender, System::ComponentModel::RunWorkerCompletedEventArgs^  e)
         {
             this->textBoxFiles->AppendText(L"Scan Complete");
         }

    ref class ProgressObject : public Object
    {
    public:
        TreeNode^ rootNode;
        TreeNode^ currentNode;

        ProgressObject(TreeNode^ theRootNode, TreeNode^ theCurrentNode)
            : rootNode(theRootNode),
              currentNode(theCurrentNode)
        {
        }
    };
};
}

Answer 1

您的程序存在第 3 常见的线程错误。数字 1 和 2 是线程竞争和死锁，BackgroundWorker 非常擅长帮助您避免那些讨厌的问题。但它并不能帮助您避免第 3 种情况，即 消防水带错误。这里的心理形象是试图从运行宁消防水龙带喝水，无论你如何努力吞咽，你都无法避免溢出水。

这里的水就是worker生产出来的TreeNodes。您的文件系统速度很快，可以非常高的速度将它们吐出。特别是第二次运行你的程序和所有文件数据都来自文件系统缓存。每秒数万。

口是你程序中的UI线程，它需要将这些节点添加到TreeView中并生成一个paint使它们可见。充其量它可以每秒添加数百个。

一旦您的工作人员首次调用 ReportProgress()，UI 线程就会开始分派调用请求。它通过调用您的 ProgressChanged 事件处理程序来执行请求。问题是，一旦完成，就会有另一个调用请求在等待。它永远无法赶上并清空调用队列。它消耗了 100% 的核心，除了调用您的 ProgressChanged 事件处理程序之外什么都不做。

并停止执行其正常职责，即发送操作系统通知。其中包括输入，您会看到它不再响应鼠标点击和键盘输入。还有绘画，一个低优先级的任务，只有在没有其他事情需要做的时候才会执行。

它没有死锁或冻结，您会看到它在工作线程完成后立即恢复正常。通常在 worker 完成几秒钟后，它仍然需要处理队列中积压的调用请求。当你关掉消防水带时，它会起作用，用 Thread.Sleep() 减慢工人的速度，这样你就可以足够快地吞咽。

您需要不止一种解决方法来保持线程平衡：

不要如此频繁地调用 ReportProgress()，在 List<TreeNode^>^ 中收集节点，直到有一百个节点为止。请牢记线程安全，您必须在 ReportProgress() 调用后创建一个新列表。
在您的 ProgressChanged 事件处理程序中使用 TreeView.Items.AddRange() 方法，这比一次添加一个要高效得多。
避免 TreeView 做太多工作来绘制节点，在启动工作程序时调用其 BeginUpdate() 方法，在 RunWorkerCompleted 事件处理程序中调用 EndUpdate()。您会以这种方式错过 "live" 更新，但这无关紧要，无论如何，用户没有任何机会快速阅读它们。
考虑到工作人员完成之前根本不更新 TreeView，因为实时视图无论如何都不是很有趣。在 RunWorkerCompleted 事件处理程序中执行此操作。

为什么我的 C++/CLI 应用程序没有响应，即使我使用了 BackgroundWorker？

Why is my C++/CLI app unresponsive even when I've use a BackgroundWorker?

winforms

visual-c++

treeview

backgroundworker