Example:
/Parent
<SomeTemplate event="#ThisEvent"/>
#code{
private async Task ThisEvent()
{
}
/Child
#Code {
[Parameter]
public EventCallback event{ get; set; }
}
Is there a way to "check" if "event" has been passed to the Child as parameter ?
I want to use this in the Child to decide "what" this implementation of this Template should show and what not
The only Solution i have is to pass additional bool values to do so, im looking for a away to avoid that
Here's how to check if a delegate has been assigned to the callback. I've set up the check to throw a Debug break if nothing has been assigned.
Also note the EditorRequired setting on the parameter which will produce a warning in the editor if that's what you want.
#using System.Diagnostics;
<h3>CallbackComponent</h3>
#code {
[Parameter, EditorRequired] public EventCallback<int> MyEventCallback { get; set; }
protected override void OnInitialized()
{
Debug.Assert(this.MyEventCallback.HasDelegate);
}
private async Task OnClick(MouseEventArgs e)
{
await this.MyEventCallback.InvokeAsync(1);
}
}
Checking for whether a delegate has been assigned is what you are after:
public EventCallback MyEventCallback { get; set; }
public async Task MyHandler()
{
if (MyEventCallback.HasDelegate)
{
await MyEventCallback.InvokeAsync();
}
}
I have implemented an IAsyncAuthorizationFilter/IActionFilter filter and implemented TypeFilterAttribute for the filter. When I add the attribute to both the controller and action, the action filter does not appear to override the controller level filter.
public class MyAuthorizeAttribute : TypeFilterAttribute
{
public MyAuthorizeAttribute (bool redirectOnFailure = true)
: base(typeof(MyFilter))
{
Arguments = new object[]
{
redirectOnFailure
};
}
}
public class MyFilter: IAsyncAuthorizationFilter, IActionFilter
{
public bool RedirectOnFailure { get; set; }
public MyFilter(bool redirectOnFailure)
{
RedirectOnFailure = redirectOnFailure;
}
public void OnActionExecuting(ActionExecutingContext context)
{
if (context.Controller is Controller controller)
{
// Do some work
if (true)
{
if (!RedirectOnFailure)
{
context.Result = new JsonResult("Your session has expired.");
}
else
{
context.Result = new RedirectResult("LoginUrl");
}
return;
}
}
}
public void OnActionExecuted(ActionExecutedContext context)
{
// Do nothing
}
public virtual async Task OnAuthorizationAsync(AuthorizationFilterContext context)
{
// Do work
}
}
The redirectOnFailure will be true for the Index action even though the filter specified false. In ASP.NET MVC, the action filter would override the controller filter. You could have a default for all actions but override specific actions with different properties/parameters. Can you not do this in Core?
[MyAuthorize]
public class HomeController : Controller
{
[MyAuthorize(redirectOnFailure: false)]
public IActionResult Index()
{
// Do work
}
}
As per the Microsoft website, filters do not override each other. They simply run one after the other in the order described in the cited document.
Just because the same attribute is put in both the controller and the action doesn't mean that ASP.net will say "ah, you probably want to override the class-level attribute". That's just not how it works.
If you want override logic, you need to write override logic.
Here's a sample made for .Net 6. The magic is done by the FindEffectivePolicy() method. This sample shows how to compare the current object against the effective one and only run the logic if the comparison matches.
public class MyFilter : IAsyncAuthorizationFilter
{
#region Properties
public string Name { get; }
#endregion
#region Constructors
public MyFilter(string name)
{
Name = name;
}
#endregion
#region IAsyncAuthorizationFilter
public Task OnAuthorizationAsync(AuthorizationFilterContext context)
{
var effectiveAtt = context.FindEffectivePolicy<MyFilter>();
System.Diagnostics.Debug.Print($"Effective filter's name: {effectiveAtt?.Name}");
System.Diagnostics.Debug.Print($"Am I the effective attribute? {this == effectiveAtt}");
if (this == effectiveAtt)
{
// Do stuff since this is the effective attribute (policy).
}
else
{
// ELSE part probably not needed. We just want the IF to make sure the code runs only once.
}
return Task.CompletedTask;
}
#endregion
}
I have created a custom attribute and I am trying to retrieve the value of this custom attribute in asp.net action filter but it seems to be unavailable. What am I doing wrong?
[AttributeUsage(AttributeTargets.Method, Inherited = true)]
public sealed class MyCustomAttribute : Attribute
{
MyCustomAttribute(string param)
{
}
}
public class MyCustomActionFilter : IActionFilter
{
public void OnActionExecuted(ActionExecutedContext context)
{
throw new NotImplementedException();
}
public void OnActionExecuting(ActionExecutingContext context)
{
// unable to find my custom attribute here under context.Filters or anywhere else.
}
}
[HttpGet]
[MyCustomAttribute ("test123")]
public async Task<Details> GetDetails(
{
}
What you want to achieve is a little more complicated if you want to do it yourself (ie. reflecting attribute value from method of Controller).
I would recommend using built-in attribute filters from ASP.NET Core (more in ASP.NET Core documentation), in your example:
public class MyCustomActionAttribute : ActionFilterAttribute
{
private readonly string param;
public MyCustomActionAttribute(string param)
{
this.param = param;
}
public override void OnActionExecuting(ActionExecutingContext context)
{
var paramValue = param;
base.OnActionExecuting(context);
}
}
and annotating your controller action like this:
[HttpGet]
[MyCustomAction("test123")]
public async Task<Details> GetDetails()
{
}
I'm creating a custom model binder for a view model, implementing IModelBinder
I have a lot of properties in my view model, the majority of which do not need any custom binding. Rather than explicitly set all of the property values on my model individually from the ModelBindingContext, I would to be able to get the framework to bind the model for me, then I would carry out any custom binding:
public class ApplicationViewModelBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null)
{
throw new ArgumentNullException(nameof(bindingContext));
}
// get .net core to bind values on model
// Cary out any customization of the models properties
bindingContext.Result = ModelBindingResult.Success(bindingContext.Model);
return Task.CompletedTask;
}
}
Basically I want to carry out the default model binding, then apply custom binding, similar to the approach taken in this SO post but for .NET Core, not framework.
I assumed applying the default binding would be straight forward, but haven't been able to find out how to do so. I believe the solution would involve ComplexTypeModelBinder and ComplexTypeModelBinderProvider classes, but can't seem to find out how to go about it.
I know I could just make any changes when the POST request hits my controller method, but this seem the wrong place and wrong time to do so.
For custom ComplexTypeModelBinder, you could inherit from ComplexTypeModelBinder.
Model
public class BinderModel
{
public int Id { get; set; }
public string Name { get; set; }
public string BinderValue { get; set; }
}
Controller Action
[HttpPost]
public void Post([FromForm]BinderModel value)
{
}
CustomBinder
public class CustomBinder : ComplexTypeModelBinder
{
private readonly IDictionary<ModelMetadata, IModelBinder> _propertyBinders;
public CustomBinder(IDictionary<ModelMetadata, IModelBinder> propertyBinders)
: base(propertyBinders)
{
_propertyBinders = propertyBinders;
}
protected override Task BindProperty(ModelBindingContext bindingContext)
{
if (bindingContext.FieldName == "BinderValue")
{
bindingContext.Result = ModelBindingResult.Success("BinderValueTest");
return Task.CompletedTask;
}
else
{
return base.BindProperty(bindingContext);
}
}
protected override void SetProperty(ModelBindingContext bindingContext, string modelName, ModelMetadata propertyMetadata, ModelBindingResult result)
{
base.SetProperty(bindingContext, modelName, propertyMetadata, result);
}
}
CustomBinderProvider
public class CustomBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (context.Metadata.IsComplexType && !context.Metadata.IsCollectionType)
{
var propertyBinders = new Dictionary<ModelMetadata, IModelBinder>();
for (var i = 0; i < context.Metadata.Properties.Count; i++)
{
var property = context.Metadata.Properties[i];
propertyBinders.Add(property, context.CreateBinder(property));
}
//var loggerFactory = context.Services.GetRequiredService<ILoggerFactory>();
//return new ComplexTypeModelBinder(propertyBinders, loggerFactory);
return new CustomBinder(propertyBinders);
}
return null;
}
}
Inject provider
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc(options => {
options.ModelBinderProviders.Insert(0, new CustomBinderProvider());
});
}
ComplexTypeModelBinder has unfortunately been deprecated in .Net 5.0, and it's counterpart, ComplexObjectModelBinder, is sealed, so you can't extend from it.
But, you can work around that. ComplexObjectModelBinderProvider is public, and you can use that to create a ComplexObjectModelBinder. Thus, if you make your own custom IModelBinderProvider, you can have the constructor accept a ComplexObjectModelBinderProvider argument, and make use of that to make a ComplexObjectModelBinder. Then, you can pass that to your custom IModelBinder, where it'll happily do its custom work before falling back to the ComplexObjectModelBinder you supplied.
Here's an example. First, your IModelBinder. This example shows that you can use DI if you want to. (In this example, say we needed a DbContext.)
public class MyCustomModelBinder : IModelBinder
{
private readonly IModelBinder _defaultBinder;
private readonly DbContext _dbContext;
public MyCustomModelBinder(IModelBinder defaultBinder, DbContext dbContext)
{
_defaultBinder = defaultBinder;
_dbContext = dbContext;
}
public override Task BindModelAsync(ModelBindingContext bindingContext)
{
// -do custom work here-
return _defaultBinder.BindModelAsync(bindingContext);
}
}
However, in order to use DI on your custom model binder, you'll need a helper class. The problem is, when IModelBinderProvider is called, it won't have access to all the services in a typical request, like your DbContext for example. But this class will help:
internal class DIModelBinder : IModelBinder
{
private readonly IModelBinder _rootBinder;
private readonly ObjectFactory _factory;
public DIModelBinder(Type binderType, IModelBinder rootBinder)
{
if (!typeof(IModelBinder).IsAssignableFrom(binderType))
{
throw new ArgumentException($"Your binderType must derive from IModelBinder.");
}
_factory = ActivatorUtilities.CreateFactory(binderType, new[] { typeof(IModelBinder) });
_rootBinder = rootBinder;
}
public Task BindModelAsync(ModelBindingContext bindingContext)
{
var requestServices = bindingContext.HttpContext.RequestServices;
var binder = (IModelBinder)_factory(requestServices, new[] { _rootBinder });
return binder.BindModelAsync(bindingContext);
}
}
Now you're ready to write the custom IModelBinderProvider:
public class MyCustomModelBinderProvider : IModelBinderProvider
{
private readonly IModelBinderProvider _rootProvider;
public MyCustomModelBinderProvider(IModelBinderProvider rootProvider)
{
_rootProvider = rootProvider;
}
public IModelBinder? GetBinder(ModelBinderProviderContext context)
{
if (context.Metadata.ModelType == typeof(MyModel))
{
var rootBinder = _rootProvider.GetBinder(context)
?? throw new InvalidOperationException($"Root {_rootProvider.GetType()} did not provide an IModelBinder for MyModel.");
return new DIModelBinder(typeof(MyCustomModelBinder), rootBinder);
}
return null;
}
}
Finally, in your startup file where you configure services, you can grab the ComplexObjectModelBinderProvider instance, use that to create a new instance of your MyCustomModelBinderProvider, and insert that into the ModelBinderProviders.
services.AddMvc(options =>
{
var fallbackProvider = options.ModelBinderProviders
.First(p => p is ComplexObjectModelBinderProvider);
var myProvider = new MyCustomModelBinderProvider(fallbackProvider);
options.ModelBinderProviders.Insert(0, myProvider);
})
I have tab pages implementing different views, but I cannot initialize each of the tabs when navigating.
<TabbedPage.Children>
<tabPages:Page1/>
<tabPages:Page2/>
<tabPages:Page3/>
</TabbedPage.Children>
So what I did was to use IActiveAware as prism documentation suggested to know which tab page is currently active. So I have this class:
public abstract class TabbedChildViewModelBase : BaseViewModel, IActiveAware, INavigationAware, IDestructible
protected bool IsInitalized { get; set; }
private bool _IsActive;
public bool IsActive
{
get
{
return _IsActive;
}
set
{
SetProperty(ref _IsActive, value, RaiseIsActiveChanged);
}
}
public event EventHandler IsActiveChanged;
public virtual void OnNavigatingTo(NavigationParameters parameters)
{
}
protected virtual void RaiseIsActiveChanged()
{
IsActiveChanged?.Invoke(this, EventArgs.Empty);
}
public virtual void Destroy()
{
}
}
So each child view models inherits the child view model base:
public class Page1 : TabbedChildViewModelBase
{
public CurrentSeaServiceViewModel()
{
IsActiveChanged += HandleIsActiveTrue;
IsActiveChanged += HandleIsActiveFalse;
}
private void HandleIsActiveTrue(object sender, EventArgs args)
{
if (IsActive == false)
{
TestLabelOnly = "Test";
}
// Handle Logic Here
}
private void HandleIsActiveFalse(object sender, EventArgs args)
{
if (IsActive == true) return;
// Handle Logic Here
}
public override void Destroy()
{
IsActiveChanged -= HandleIsActiveTrue;
IsActiveChanged -= HandleIsActiveFalse;
}
}
The problem is, the child vm isn't initializing. Is there something needed in order to implement IActiveAware properly nor launching the IsActive property
I still used IActiveAware unfortunately, to make the childtabbedviewmodel work you need to bind the page to its own view model.
So here's what I did:
<TabbedPage.Children>
<views:ChildPage1>
<views:ChildPage1.BindingContext>
<viewModels:ChildPage1ViewModel/>
</views:ChildPage1.BindingContext>
</views:ChildPage1>
<views:ChildPage2>
<views:ChildPage2.BindingContext>
<viewModels:ChildPage2ViewModel/>
</views:ChildPage2.BindingContext>
</views:ChildPage2>
</TabbedPage.Children>
I used the property BindingContext of my views and
using IActiveAware I would also know what tab is currently active. Hope anyone helps this who finds trouble binding the child pages of a tab.