在HttpClient异常时显示AlertDialog (Xamarin Android)

private async Task<string> MakeHttpRequest(string url)
{
    try
    {
        using (HttpClient client = new HttpClient())
        {
            HttpResponseMessage response = await client.GetAsync(url);
            response.EnsureSuccessStatusCode();
            string result = await response.Content.ReadAsStringAsync();
            return result;
        }
    }
    catch (Exception ex)
    {
        ShowErrorDialog("网络请求失败", ex.Message);
        return null;
    }
}

private void ShowErrorDialog(string title, string message)
{
    AlertDialog.Builder builder = new AlertDialog.Builder(this);
    builder.SetTitle(title);
    builder.SetMessage(message);
    builder.SetPositiveButton("确定", (sender, args) => { });
    AlertDialog dialog = builder.Create();
    dialog.Show();
}

string url = "https://example.com/api/data";
string result = await MakeHttpRequest(url);
if (result != null)
{
    // 处理返回的结果
}