C＃Web客户端使用异步和返回数据 [英] C# WebClient Using Async and returning the data

问题描述

好吧，我一直在使用DownloadDataAsync并让它字节还给我的时候遇到了一个问题。这是code我使用的：

Alright, I have ran into a problem when using DownloadDataAsync and having it return the bytes to me. This is the code I am using:

    private void button1_Click(object sender, EventArgs e)
    {
        byte[] bytes;
        using (WebClient client = new WebClient())
        {
            client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(DownloadProgressChanged);
            bytes = client.DownloadDataAsync(new Uri("http://example.net/file.exe"));
        }
    }
    void DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
    {
        double bytesIn = double.Parse(e.BytesReceived.ToString());
        double totalBytes = double.Parse(e.TotalBytesToReceive.ToString());
        double percentage = bytesIn / totalBytes * 100;
        label1.Text = Math.Round(bytesIn / 1000) + " / " + Math.Round(totalBytes / 1000);

        progressBar1.Value = int.Parse(Math.Truncate(percentage).ToString());
        if (progressBar1.Value == 100)
        {
            MessageBox.Show("Download Completed");
            button2.Enabled = true;
        }
    }

我得到的错误是无法隐式转换类型'无效'到'字节[]'。

The error I get is "Cannot implicitly convert type 'void' to 'byte[]'"

反正我有可以让这一切成为可能，并给我字节它完成下载后？取出时它工作正常字节=

Is there anyway I can make this possible and give me the bytes after it is done downloading? It works fine when removing "bytes =".

推荐答案

由于 DownloadDataAsync 方法是异步的，它不返回一个直接结果。您需要处理 DownloadDataCompleted 事件：

Since the DownloadDataAsync method is asynchronous, it doesn't return an immediate result. You need to handle the DownloadDataCompleted event :

client.DownloadDataCompleted += new DownloadDataCompletedEventHandler(DownloadCompleted);
...


private static void DownloadCompleted(Object sender, DownloadDataCompletedEventArgs e)
{
    byte[] bytes = e.Result;
    // do something with the bytes
}

这篇关于C＃Web客户端使用异步和返回数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！