使用Dapr 客戶端 處理服務調用，需要遵循的他的模式，通常代碼是這個樣子的：

var client = DaprClient.CreateInvokeHttpClient(appId: "routing"); var response = await client.GetAsJsonAsync($"/accounts/{17}", cancellationToken); var account = await response.Content.ReadFromJsonAsync<Account>(cancellationToken: cancellationToken);我更希望是這樣子調用:

public interface IBank
{
??????????? [HttpGet("/accounts/{accountId}")]
??????????? Task<Account> GetUser(string accountId, CancellationToken cancellationToken = default);

?????????? [HttpPost("/deposit")]
??????????? Task<Account> Deposit([JsonContent] Transaction transaction, CancellationToken cancellationToken = default);

?????????? [HttpPost("/withdraw")]
??????????? [RawReturn(Enable =true, EnsureSuccessStatusCode = false)]
??????????? Task<HttpResponseMessage> Withdraw([JsonContent] Transaction transaction, CancellationToken cancellationToken = default);
}

var account = await bankClient.GetUser("17", cancellationToken);我們可以用 Refit，RestEase 或者是 WebApiClientCore 來達到這樣的效果， 那么在Dapr 里面使用這些庫如何做到呢， 在Dapr的客戶端庫里面有一個Handler 的官方實現：InvocationHandler。搭配這個InvocationHandler 就可以和這幾個庫，在本文中，我們重點介紹Dapr Client 如何搭配 WebApiClientCore。

public interface IBank
{
????????? [HttpGet("/accounts/{accountId}")]
????????? Task<Account> GetUser(string accountId, CancellationToken cancellationToken = default);

????????? [HttpPost("/deposit")]
????????? Task<Account> Deposit([JsonContent] Transaction transaction, CancellationToken cancellationToken = default);

????????? [HttpPost("/withdraw")]
????????? [RawReturn(Enable =true, EnsureSuccessStatusCode = false)]
????????? Task<HttpResponseMessage> Withdraw([JsonContent] Transaction transaction, CancellationToken cancellationToken = default);
}

? public class WebapiClientExample : Example
?? {
?????? public override string DisplayName => "WebapiClient";

????? private IBank bankClient;

????? public WebapiClientExample(IBank bank)
?????? {
?????????? bankClient = bank;
?????? }

????? public override async Task RunAsync(CancellationToken cancellationToken)
?????? {
?????????? var options = new JsonSerializerOptions(JsonSerializerDefaults.Web);

?????????? // Scenario 1: Check if the account already exists.
?????????? Account? account = null;
?????????? try
?????????? {
?????????????? account = await bankClient.GetUser("17", cancellationToken);
?????????? }
?????????? catch (ApiException ex)
?????????? {
?????????????? // Account does not exist.
?????????? }

????????? Console.WriteLine($"Scenario 1: account '17' {(account is null ? "does not exist" : "already exists")}");

????????? // Scenario 2: Deposit some money
?????????? var transaction = new Transaction()
?????????? {
?????????????? Amount = 100m,
?????????????? Id = "17",
?????????? };

????????? // read updated balance
?????????? account = await bankClient.Deposit(transaction, cancellationToken);
?????????? Console.WriteLine($"Scenario 2: account '17' has '{account?.Balance}' money");

????????? // Scenario 3: Handle a validation error without exceptions
?????????? transaction = new Transaction()
?????????? {
?????????????? Amount = 1_000_000m,
?????????????? Id = "17",
?????????? };
?????????? HttpResponseMessage response = null;

????????? response = await bankClient.Withdraw(transaction, cancellationToken);
?????????? if (response.StatusCode != HttpStatusCode.BadRequest)
?????????? {
?????????????? // We don't actually expect this example to succeed - we expect a 400
?????????????? Console.WriteLine("Something went wrong :(");
?????????????? return;
?????????? }
?????????? var problem = await response.Content.ReadFromJsonAsync<ProblemDetails>(cancellationToken: cancellationToken);
?????????? Console.WriteLine($"Scenario 3: got the following errors:");
?????????? foreach (var kvp in problem!.Errors)
?????????? {
?????????????? Console.WriteLine($"{kvp.Key}: {string.Join(", ", kvp.Value)}");
?????????? }
?????? }
?? }

var services = new ServiceCollection();
???????????? services.AddTransient<Example, WebapiClientExample>();
???????????? services.AddLogging();

??????????? services
???????????????? .AddScoped<InvocationHandler>()
???????????????? .AddHttpApi<WebapiClientExample.IBank>(o => o.HttpHost = new Uri("http://bank"))
?????????????????.AddHttpMessageHandler<InvocationHandler>();
??????????? var serviceprovider = services.BuildServiceProvider();

代碼的核心部分就在于上面紅色的部分，我們把InvocationHandler 加入到AddHttpApi ，就可以和 dapr 一起玩耍了。

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