Try-Catch不显示带有等待的消息对话框

Question

以下代码成功从Web服务获取数据并将其显示在Windows 8桌面应用程序中。

HttpClient client = new HttpClient(); 
HttpResponseMessage response = await client.GetAsync("http://localhost:12345/api/items"); 

var info = new List<SampleDataGroup>(); 

if (response.IsSuccessStatusCode) 
{ 
    var content = await response.Content.ReadAsStringAsync(); 

    var item = JsonConvert.DeserializeObject<dynamic>(content); 

    foreach (var data in item) 
    { 
     var infoSect = new SampleDataGroup 
     (
      (string)data.Id.ToString(), 
      (string)data.Name, 
      (string)"", 
      (string)data.PhotoUrl, 
      (string)data.Description 
     ); 
     info.Add(infoSect); 
    } 
} 
else 
{ 
    MessageDialog dlg = new MessageDialog("Error"); 
    await dlg.ShowAsync(); 
} 

但是，这确实需要互联网连接才能正常工作。每次没有互联网连接时，该应用程序崩溃。

如何在此代码中编写try catch语句以在网络连接不起作用时显示弹出消息？

编辑：

我想下面使用MessageDialog，而这种停止应用程序崩溃，但它并不带来了该消息。

 catch (Exception ex) 
     { 
      MessageDialog err = new MessageDialog(ex.Message); 

     } 

Answer 1

你不需要

string errorMessage = string.Empty; 

try 
{ 

    HttpClient client = new HttpClient(); 
    HttpResponseMessage response = await  
    client.GetAsync("http://localhost:12345/api/items"); 

    var info = new List<SampleDataGroup>(); 

    if (response.IsSuccessStatusCode) 
    { 
    var content = await response.Content.ReadAsStringAsync(); 

    var item = JsonConvert.DeserializeObject<dynamic>(content); 

    foreach (var data in item) 
    { 
     var infoSect = new SampleDataGroup 
     (
      (string)data.Id.ToString(), 
      (string)data.Name, 
      (string)"", 
      (string)data.PhotoUrl, 
      (string)data.Description 
     ); 
     info.Add(infoSect); 
    } 
    } 
    else 
    { 
     errorMessage = "Error"; 
    }  
}  
catch (Exception ex) 
{ 
    ErrorMessage = ex.Message; 
} 

if (errorMessage != string.Empty) 
{ 
    MessageDialog dlg = new MessageDialog(errorMessage); 
    await dlg.ShowAsync(); 
} 

？