无法将 BackgroundWorker 进度百分比调整为任务的实际百分比答案

【问题标题】：Cannot Adapt BackgroundWorker progress percentage to the real percentage of the task无法将 BackgroundWorker 进度百分比调整为任务的实际百分比
【发布时间】：2015-06-29 13:28:49
【问题描述】：

我编写了一个程序，它读取一个短视频，然后以降低的 FPS 写入几百帧。它运行良好，但“if”循环阻塞了 UI。我尝试创建一个 backgroudWorker 来处理“if”循环，同时可以显示 UI 值，并且可以通过“取消”按钮中断该过程。我的问题是：我无法让“if”循环遍历所有帧：

for (i = 0; i < frames_number; i++)

到最后一帧！它停在 100，即使我尝试了多种解决方案将“i”的进度转换为百分比，例如：

progress = System::Convert::ToInt32((100*(i / frames_number)));

或

progress = (int)((float)i / (float)frames_number *100);

以下是代码的重要sn-ps：

private: System::Void CreateSlowMo_Click(System::Object^  sender, System::EventArgs^  e) {
        VideoCapture inputVideo(videoToOpenNameStr);
        if (!inputVideo.isOpened()) {
            MessageBox::Show(L"Error"); 
        }       
        fps =   int(inputVideo.get(CAP_PROP_FPS)); // get the frame rate of the video
        frames_number = int(inputVideo.get(CAP_PROP_FRAME_COUNT));     // get the total frames in the video
        this->progressBar1->Maximum = frames_number;      // Initilize the progress bar's maximum to the number of frames       
        outputVideo.open(name, CV_FOURCC('M', 'J', 'P', 'G'), fps_wanted, resolution, true);  // Create an output video 
        if (outputVideo.isOpened())
        {   
            this->backgroundWorker1->RunWorkerAsync(progress);     // Delegating the blocking operations to the background worker        
        }
        else {
            MessageBox::Show(L"Error creating the video");
            CreateSlowMo_button->Enabled = true;
        }       
    }

backgroundWorker1_DoWork：

private: System::Void backgroundWorker1_DoWork(System::Object^  sender, System::ComponentModel::DoWorkEventArgs^  e) {

    progress = (int)e->Argument; // get the intial value of the argument
    for (i = 0; i < frames_number; i++)
    {    
        inputVideo >> source; // read frame 

        if (backgroundWorker1->CancellationPending) {   // check if the User clicked on "Cancel"
            e->Cancel = true;
            break;    // Stop the convertion
        }
        if (source.empty()) { // we reached the last frame
            break;
            //  CreateSlowMo_button->Enabled = true;
        }    
        if (progress > 100) 
        { // verify we didn't exceed 100% of the task
            backgroundWorker1->ReportProgress(100);
            break;
        }       
        outputVideo << source; // write the frame to the output video
        progress = (int)(((float)i / (float)frames_number)* 100);
        backgroundWorker1->ReportProgress(progress);        
    }     
    this->backgroundWorker1->ReportProgress(100);
    e->Result = progress;    
}

backgroundWorker1_ProgressChanged：

private: System::Void backgroundWorker1_ProgressChanged(System::Object^  sender, System::ComponentModel::ProgressChangedEventArgs^  e) {
    this->progressBar1->Value = e->ProgressPercentage;
    toolStripStatusLabel1->Text = "Processing..." + progressBar1->Value.ToString() + "%";
    richTextBox6->Text = e->ProgressPercentage.ToString();  
}

backgroundWorker1_RunWorkerCompleted：

private: System::Void backgroundWorker1_RunWorkerCompleted(System::Object^  sender, System::ComponentModel::RunWorkerCompletedEventArgs^  e) {
     // in case the background process is finished with a cancel
    if (e->Cancelled) 
    {
        toolStripStatusLabel1->Text = "Task Cancelled";
    }
    // check if an error occurred in the backgroud process
    else if (e->Error != nullptr)
    { 
        toolStripStatusLabel1->Text = "Error while creating the SlowMo";
    }
    else 
    {   // task completed normally
        this->toolStripStatusLabel1->Text = "SlowMo Created successfully!";
        this->cancel_button->Enabled = false;
        MessageBox::Show(L"Finished creating the sloMo");
        this->toolStripStatusLabel1->Text = "Done";
        this->CreateSlowMo_button->Enabled = true;   
        this->richTextBox5->Text = "value " + e->Result;
    }
}

这里是结果的一些截图（我添加了文本框来可视化 'i'、'progress' 和 e->result 的值）'i' 和 'progress' 是 int=0，在文件 'variables 中定义.h'

extern int i ;
extern int progress;

和'variables.cpp'：

int i = 0;
int progress =0;

【问题讨论】：

您的代码中有一个明显的错误，您正在从 0..100 计算进度，但 ProgressBar::Maximum 不是 100。简单的解决方法是删除 this->progressBar1->Maximum = frames_number; 分配。跨度>
我改变了它，但它只影响了progressBar（它是完全绿色的）并且不能通过所有的帧（这里是589）。结果如下：i.imgur.com/H6rP9xZ.png i.imgur.com/wYAYKSO.png

标签： c++ visual-c++ visual-studio-2013 backgroundworker

【解决方案1】：

您检查过frames_number 的值吗？或者，如果您在for 循环中的任何if 语句在执行期间的任何时候变为真？

我怀疑frames_number 在for 循环之前获得了不正确的值，或者source.empty() 变为真。

【讨论】：