invalidoperationexception

ASP.NET Core – Only one parameter per action may be bound from body

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When you have multiple parameters on an action method that are bound to the request body (implicitly or explicitly), you get the following fatal exception upon starting the web API: System.InvalidOperationException: Action ‘RecipeController.Post’ has more than one parameter that was specified or inferred as bound from request body. Only one parameter per action may be … Read more

C# – How to use JsonNode to read, write, and modify JSON

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When you don’t want to create classes for JSON (de)serialization, one option is to use JsonNode. This allows you work with JSON as a mutable DOM that consists of JsonNode objects (JsonObject, JsonArray, JsonValue). You can use it to read, write, and modify JSON. Here’s an example. Let’s say you have the following JSON that … Read more

C# – How to use JsonExtensionData

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Use the JsonExtensionData attribute (in System.Text.Json) to deserialize properties that aren’t part of the class. Without this, JSON fields that don’t match a property are simply ignored and the returned object will have null properties. Here’s an example of adding this attribute to a dictionary property: Now when you deserialize JSON to this Person class, … Read more

InvalidOperationException: Unable to resolve service for type

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When the built-in dependency injection functionality is trying to create a type, it tries to resolve all of the constructor parameters. If it can’t resolve one of the parameters, it’ll throw a variation of one of these exceptions: The error you get will depend on how you’re doing registration. First, I’ll show the solution. Then … Read more

Collection was modified; enumeration operation may not execute

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If you try to add/remove items from a collection while it’s being looped over in a foreach loop (enumerated), then you’ll get the following exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.at System.Collections.Generic.List`1.Enumerator.MoveNext() This error can happen in two scenarios: The solution to this problem depends on which scenario you’re in. In this … Read more

Serializer options cannot be changed once serialization or deserialization has occurred

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Problem When using System.Text.Json, it’s a good idea to reuse JsonSerializerOptions objects. This leads to a massive 200x speedup in subsequent calls to the serializer. The downside is you can’t change properties on the options object after you’ve passed it in a Serialize()/Deserialize() call. You’ll get the exception: System.InvalidOperationException: Serializer options cannot be changed once … Read more

Invoke or BeginInvoke cannot be called on a control until the window handle has been created

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Problem In a WinForms project, if you try to call Invoke/BeginInvoke before the window handle is created, you’ll get the following exception: System.InvalidOperationException: Invoke or BeginInvoke cannot be called on a control until the window handle has been created Because this exception happens while the form is initializing, it typically results in the form not … Read more

C# – Switch from using HttpWebRequest to HttpClient

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There are many reasons to use HttpClient instead of HttpWebRequest. For one, the MSDN docs strongly recommends against using HttpWebRequest, and using HttpClient instead. That should be enough, but if you need a little more convincing, take a look at the Practical reasons to not use HttpWebRequest section below. In addition to explaining why not … Read more

C# – Check if a nullable bool is true

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You can’t use nullable bools (bool?) exactly like regular bools, because they aren’t the same thing. When you try to use them like regular bools, you run into compiler errors and runtime exceptions. Instead, you have to explicitly compare the nullable bool with true/false. Here’s an example of checking if a nullable bool is true … Read more

Error: Synchronous operations are disallowed

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Problem When you try to do a synchronous IO operation in ASP.NET Core (such as writing to a file), you get the following exception: System.InvalidOperationException: ‘Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true The reason you’re getting this is because server option AllowSynchronousIO is false. Starting in ASP.NET Core 3.0, this is … Read more

Error: Sequence contains no elements

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Problem When you call .First() on an empty IEnumerable, you get the following exception: System.InvalidOperationException: Sequence contains no elements Solution Option 1 – Use .FirstOrDefault() instead of .First() When the IEnumerable is empty, .FirstOrDefault() returns the default value for the type. For reference types this returns null. For value types this returns 0 or that … Read more

How to update UI from another thread

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I often need to be able to run multiple threads and update the UI based on the results. For example, I may need to execute GET requests to 10 different endpoints concurrently, and then report their results in a datagrid as they come back. The problem is you can’t just update the UI from any … Read more