C#•15mo ago

❔ Cast is not valid when casting interface to comcrete impl

this is my concrete imp: public class TempFile : IBrowserFile { public TempFile(string uuid, string name, long size, string contentType) { Uuid = uuid; Name = name; Size = size; ContentType = contentType; } public TempFile() { } public string Uuid { get; set; } = ""; public string ContentType { get; set; } = ""; public string Name { get; set; } = ""; public long Size { get; set; } public DateTimeOffset LastModified => throw new NotImplementedException(); public Stream OpenReadStream(long maxAllowedSize = 512000, CancellationToken cancellationToken = default) { throw new NotImplementedException(); } } ========================= this is where im trying to cast ibrowserFile as TempFile and getting invalid Cast. private async Task UploadFileAsync(IBrowserFile file) { if (file == null) return; if (EditModel == null) { throw new Exception("No edit model"); } if (EditModel.Id == 0) { var result = await this.EmployeeComptesDepensesService.UploadTemporaryAttachmentFileAsync(file); if (!result.ApiCallSuccess) { this.serverResponseValidator?.DisplayErrors(result.ServerErrors, result.ApiCallResultErrorMessage); } else { try { TempFile tf = (TempFile)file; tf.Uuid = result.ResultModel?.Result!; EditModel.TempFiles.Add(tf);
} catch (Exception ex) {
this.serverResponseValidator?.DisplayErrors(null, $"cast error {ex.Message}"); } } } What's going on???

8 Replies

Azrael•15mo ago

$code

MODiX•15mo ago

To post C# code type the following: ```cs // code here ``` Get an example by typing $codegif in chat If your code is too long, post it to: https://paste.mod.gg/

Hazel 🌊💃•15mo ago

While you know a cat is an animal, how do you know that an animal is a cat?

MODiX•15mo ago

Hazel | へいぜる

REPL Result: Failure

public class Animal { public int Id { get; set; } }
public class Cat : Animal { public string Name { get; set; } }

var thomas = new Cat { Id = 0, Name = "Thomas" };
var thomasTheAnimal = new Animal { Id = 0 };
var thomasTheCat = (Cat)thomasTheAnimal;
Console.WriteLine(thomasTheCat.Id);

public class Animal { public int Id { get; set; } }
public class Cat : Animal { public string Name { get; set; } }

var thomas = new Cat { Id = 0, Name = "Thomas" };
var thomasTheAnimal = new Animal { Id = 0 };
var thomasTheCat = (Cat)thomasTheAnimal;
Console.WriteLine(thomasTheCat.Id);

Exception: InvalidCastException

- Unable to cast object of type 'Animal' to type 'Cat'.

- Unable to cast object of type 'Animal' to type 'Cat'.

Compile: 653.168ms | Execution: 53.051ms | React with ❌ to remove this embed.

Hazel 🌊💃•15mo ago

This doesn't work because an animal is not a cat, even though a cat is an animal.

PatrickGOP•15mo ago

hmm i thought i could cast both directions and it would just fill the minimum fields that are part of the animal interface

cap5lut•15mo ago

nope, u would have to write such a mapping urself it could be done with implementing custom casts, but in this case it feels like a ToTempFile() method or similar has better semantics/intention is clearer

Accord•15mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Cast is not valid when casting interface to comcrete impl