Question

我正在尝试显示一个显示标签的表单，例如“更新，此窗口将在更新完成后关闭”以下载一些图像文件。我把它放在我的表格上。

private void frmExtraUpdater_Shown(object sender, EventArgs e)
    {

        for (int i = 1; i < 8; i++)
        {
            string _EmoticonURL = String.Format("https://dl.dropboxusercontent.com/u/110636189/MapleEmoticons/f{0}.bmp", i);

            WebRequest requestPic = WebRequest.Create(_EmoticonURL);

            WebResponse responsePic = requestPic.GetResponse();

            Image webImage = Image.FromStream(responsePic.GetResponseStream()); // Error

            webImage.Save(Application.StartupPath + @"\Images\f" + i + ".bmp");
        }
    }

然而..一旦显示表单，标签甚至不显示，因为它没有加载它（它坚持下载图像。我希望它显示标签，然后才开始下载）。

另一个问题是它抛出了“GDI +中发生了一般错误”。在webImgae.Save部分由于某种原因。

为什么？

哦，如果文件夹“图片”不存在，它会自动创建吗？

谢谢！

Answer 1

这是Jon Skeet的建议：

System.Net.WebClient webClient = new System.Net.WebClient();
webClient.DownloadFile(String.Format("https://dl.dropboxusercontent.com/u/110636189/MapleEmoticons/f{0}.bmp", i), Application.StartupPath + @"\Images\f" + i + ".bmp");

使用后台工作程序更新任何UI组件

BackgroundWorker backTask = new BackgroundWorker();
    public frmExtraUpdater()
    {
        backTask.DoWork += backTask_DoWork;
        backTask.RunWorkerCompleted += backTask_RunWorkerCompleted;
    }
    private void frmExtraUpdater_Shown(object sender, EventArgs e)
    {
        yourLabel.Text = "Downloading";
        backTask.RunWorkerAsync();
    }

    void backTask_DoWork(object sender, DoWorkEventArgs e)
    {
        for (int i = 1; i < 8; i++)
        {
            System.Net.WebClient webClient = new System.Net.WebClient();
            webClient.DownloadFile(String.Format("https://dl.dropboxusercontent.com/u/110636189/MapleEmoticons/f{0}.bmp", i), Application.StartupPath + @"\Images\f" + i + ".bmp");
            backTask.ReportProgress(i * (100 / 8), String.Format("https://dl.dropboxusercontent.com/u/110636189/MapleEmoticons/f{0}.bmp", i));
        }
    }

    void backTask_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        yourLabel.Text = "Downloading" + e.UserState.ToString();
    }

    void backTask_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        this.Close(); 
    }

Answer 2

您应该使用async方法，使用webrequest async api（如果使用.net 4.5或sup）或者在后台线程中下载图像以避免ui线程阻塞。

您可以尝试：

    private void frmExtraUpdater_Shown(object sender, EventArgs e)
    { 
        BackgroundWorker worker = new BackgroundWorker();

        worker.DoWork += (o, d) =>
        {
            saveImages();
        };
        worker.RunWorkerCompleted += (o, f) =>
        {
            this.Close();
        };
        worker.RunWorkerAsync();
    }

    private void saveImages()
    {
        for (int i = 1; i < 8; i++)
        {
            string _EmoticonURL = String.Format("https://dl.dropboxusercontent.com/u/110636189/MapleEmoticons/f{0}.bmp", i);

            WebRequest requestPic = WebRequest.Create(_EmoticonURL);

            WebResponse responsePic = requestPic.GetResponse();

            Image webImage = Image.FromStream(responsePic.GetResponseStream()); // Error

            webImage.Save(Application.StartupPath + @"\Images\f" + i + ".bmp");
        }
    }

C＃ - 将图像下载并保存到文件夹

2 个答案: