使用后台线程、ListView 和 ProgressBar 扫描图像尺寸

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• 下载源代码 - 17.7 KB

引言

这篇文章是另一篇文章的扩展版本，我发现这篇文章非常有趣，名为 后台线程和支持取消，作者是 Andrew D. Weiss。

本文解释了如何异步运行 BackgroundWorker 线程以扫描图像尺寸。用户可以选择一个文件夹或选择特定的图像。在将图像名称插入 ListView 后，将集合对象传递给 BackgroundWorker，该线程扫描每张图像并报告进度，并在 ProgressBar 上显示。

使用代码

当添加照片时，它们存储在一个名为 PhotoCollection 的对象中，该对象继承自 List<Photo>。每张照片都有一个 FileInfo 实例和一些添加的属性。PhotoCollection 可以导出到 XML 文件，并使用 XmlParser 类从 XML 文件导入回来。

此软件可以进一步扩展为调整大小程序、重命名器、组织器，或者您想对照片集合执行的任何操作。BackgroundWorker 还可以预生成缩略图，并且 ListView 可以替换为类似于 Windows XP 或更高版本中看到的“大图标”视图。

BackgroundWorker

方法 UpdateListView_HeavyProcess() 启动线程并为其提供工作参数。方法 worker_DoWork() 将运行繁重的工作，并且每次在 worker_DoWork() 内部调用 trd.ReportProgress() 时，都会调用方法 worker_ProgressChanged()，该方法允许更新 GUI 组件。当线程完成其工作后，将调用方法 worker_RunWorkerCompleted()，该方法将结果转换为 PhotoCollection。

private void UpdateListView_HeavyProcess()
{
    // Do not try to execute the background worker if 
    // he is already busy with work
    if (!worker.IsBusy)
    {
        // Prepare the progress var
        prbProgress.Minimum = 0;
        prbProgress.Maximum = photos.Count;
        prbProgress.Value = 0;
        prbProgress.Step = 1;
        prbProgress.Enabled = true;

        // Run the worker thread, taking photos as argument
        worker.RunWorkerAsync(photos);
    }
}

private void worker_DoWork(object sender, DoWorkEventArgs e)
{
    // Create an instance that represents the running thread
    BackgroundWorker trd = sender as BackgroundWorker;

    // Cast the argument object to PhotoCollection
    PhotoCollection col = (PhotoCollection)e.Argument;
    Image img;

    // Go through each photo using indices
    for (int i = 0; i < col.Count; i++)
    {
        // If the photo HAS dimention - cancel the operation because 
        // it is VERY unlikely that the photo will be changed when
        // already added to this list
        if (col[i].PixelHeight == 0 && col[i].PixelWidth == 0)
        {
            img = Image.FromFile(col[i].FullName);
            col[i].PixelWidth = (int)img.PhysicalDimension.Width;
            col[i].PixelHeight = (int)img.PhysicalDimension.Height;
        }

        // Report back the photo number and scanned dimention
        trd.ReportProgress(i, col[i].Dimention);

        // If the thread MUST stop running!
        if (trd.CancellationPending)
        {
            // Set the e.Cancel flag so that the WorkerCompleted event
            // knows that the process was canceled.
            e.Cancel = true;

            // Save the changed object to result
            e.Result = col;

            // Report back negative value, indicating that the execution is done
            trd.ReportProgress(-1);

            // Stop running the working method
            return;
        }
    }

    // Save the changed object to result
    e.Result = col;

    // Report back negative value, indicating that the execution is done
    trd.ReportProgress(-1);
}

private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // Cast the results to the PhotoCollection object
    // owned by this thread
    photos = (PhotoCollection)e.Result;

    // Now update the whole list again!
    this.UpdateListView(true);

    // Reset the progress bar
    prbProgress.Minimum = 0;
    prbProgress.Value = 0;
    prbProgress.Enabled = false;
}

private void worker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    try
    {
        // Update the title bar at top that the program is working on some photos
        this.Text = "<" + photos[e.ProgressPercentage].Name + 
                    "> " + ProgramName;

        // Perform a progress step
        prbProgress.PerformStep();

        // Try to update the ListView by using the progress percentage
        // as an index in the ListView items
        lsvFiles.Items[e.ProgressPercentage].SubItems[2].Text = e.UserState.ToString();
    }
    catch
    {
        this.Text = ProgramName;
    }
}