Xamarin中Web API Post数据始终为空问题（VS2017环境）

Hey there, let's work through that empty POST data issue you're hitting with your setup. First, let's recap your environment to make sure we're aligned:

• IDE: Microsoft Visual Studio Professional 2017 Version 15.6.1
• .NET Framework: 4.7.02556
• Xamarin Components:
  • Xamarin 4.9.0.749 (9b0fce36d)
  • Xamarin Designer 4.10.58 (cee1369d0)
  • Xamarin.Android SDK 8.2.0.15 (HEAD/22d97e153)

Below are the most common fixes and checks to resolve this problem:

1. Validate Your Request's Content-Type Header #

This is one of the most frequent culprits. Ensure your request sends the correct Content-Type that matches the payload you're posting:

• For JSON payloads: Use application/json
• For form data: Use application/x-www-form-urlencoded

Omitting this header or setting it incorrectly will often cause the API to ignore your POST data. Here's a quick example of setting it properly in Xamarin:

var client = new HttpClient();
// Set accept header to match expected response type
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
// Wrap your data in a StringContent with correct encoding and content type
var payload = JsonConvert.SerializeObject(yourDataObject);
var content = new StringContent(payload, Encoding.UTF8, "application/json");
var response = await client.PostAsync("your-api-endpoint-url", content);

2. Double-Check Payload Serialization #

If you're using a serializer like Newtonsoft.Json, confirm your data object is being serialized correctly. Accidental [JsonIgnore] attributes, private setters, or uninitialized properties can lead to empty or incomplete payloads.

Test serialization independently to rule this out:

var serializedData = JsonConvert.SerializeObject(yourDataObject);
Console.WriteLine(serializedData); // Verify this outputs the full, expected JSON

3. Inspect the Raw Request with a Proxy Tool #

Grab a tool like Fiddler or Charles Proxy to capture the actual HTTP request leaving your app. This lets you:

• See the full request headers
• Check the raw payload being sent
• Spot redirects or hidden errors that might alter the request

This is often the fastest way to confirm if the issue is client-side (not sending data) or server-side (not parsing it correctly).

4. Verify Web API Model Binding Setup #

On the API side, make sure your controller action is configured to accept POST data properly:

• For JSON payloads, use the [FromBody] attribute on your model parameter:

  [HttpPost]
  public IHttpActionResult SubmitData([FromBody] YourRequestModel model)
  {
      // Your logic here
  }
  

• Avoid mixing [FromBody] with form-data parameters unless you're handling multi-part requests.

5. Try Switching Xamarin's HttpClient Handler #

Xamarin offers multiple HttpClient handlers: HttpClientHandler, AndroidClientHandler, and (for iOS) NSUrlSessionHandler. Sometimes the default handler has quirks with certain request types. Try explicitly using a different handler:

// For Android apps, use AndroidClientHandler
var handler = new AndroidClientHandler();
var client = new HttpClient(handler);

6. Update .NET Framework to the Latest Patch #

While .NET Framework 4.7 is stable, there were minor serialization and HTTP request fixes in later patches. Updating to the latest 4.7.x patch (like 4.7.2) can rule out framework-level bugs causing the issue.

If none of these steps resolve the problem, sharing a minimal snippet of your POST request code and the corresponding Web API action would help narrow things down further!

内容的提问来源于stack exchange，提问作者user619