c# - 任务不包含内容的定义

Question

如何克服下面的错误？我按照下面的教程进行操作，但我得到的红线表示不包含 Content 的定义。 https://www.youtube.com/watch?v=IVvJX4CoLUY

private void UploadFile_Cliked(object sender, EventArgs e)
{
    var content = new MultipartFormDataContent();
    content.Add(new StreamContent(_mediaFile.GetStream()),
        "\"file\"",
        $"\"{_mediaFile.Path}\"");
    var httpClient = new HttpClient();

    var uploadServiceBaseAddress = "http://192.168.137.1/pic/";
    var httpResponseMessage = httpClient.PostAsync(uploadServiceBaseAddress, content);
    RemotePathLabel.Text = httpResponseMessage.Content.ReadAsStringAsync();
}

'Task' does not contain a definition for 'Content' and no extension method 'Content' accepting a first argument of type 'Task' could be found (are you missing a using directive or an assembly reference?)

这是错误，但有解决办法吗？

我已经添加了这个 Microsoft.AspNet.WebApi.Client 包，但仍然失败

Answer 1

使事件处理程序异步，然后等待返回任务派生结果的函数，因为您在调用 ReadAsStringAsync 时会遇到同样的问题

private HttpClient httpClient = new HttpClient();

private async void UploadFile_Cliked(object sender, EventArgs e) {
    var content = new MultipartFormDataContent();
    content.Add(new StreamContent(_mediaFile.GetStream()),
        "\"file\"",
        $"\"{_mediaFile.Path}\"");        

    var uploadServiceBaseAddress = "http://192.168.137.1/pic/";
    var httpResponseMessage = await httpClient.PostAsync(uploadServiceBaseAddress, content);
    RemotePathLabel.Text = await httpResponseMessage.Content.ReadAsStringAsync();
}

请注意，事件处理程序是允许 async void 的规则的异常(exception)

引用 Async/Await - Best Practices in Asynchronous Programming