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| == [https://docs.microsoft.com/en-us/aspnet/core/blazor/webassembly-performance-best-practices?view=aspnetcore-5.0#ensure-cascading-parameters-are-fixed Ensure cascading parameters are fixed] == | | == [https://docs.microsoft.com/en-us/aspnet/core/blazor/webassembly-performance-best-practices?view=aspnetcore-5.0#ensure-cascading-parameters-are-fixed Ensure cascading parameters are fixed] == |
| If the {{boxx|IsFixed}} value is {{boxx|true}} ({{boxx|false}} by default), then receipients receive the initial value but do not set up any subscription to receive updates. In this case, each {{boxx|[CascadingParameter]}} is lightweight and no more expensive than a regular {{boxx|[Parameter]}}.<br> | | If the {{boxx|IsFixed}} value is {{boxx|true}} ({{boxx|false}} by default), then receipients receive the initial value but do not set up any subscription to receive updates. In this case, each {{boxx|[CascadingParameter]}} is lightweight and no more expensive than a regular {{boxx|[Parameter]}}.<br> |
| So wherever possible, you should use {{boxx|IsFixed="true"}} on cascaded values. You can do this whenever the value being supplied doesn't change over time. | | So wherever possible, you should use {{boxx|1=IsFixed="true"}} on cascaded values. You can do this whenever the value being supplied doesn't change over time. |
Version du 25 juillet 2021 à 15:51
Basic component
| Components/MyComponent.razor
|
<h1>Test</h1>
<p>@ChildContent</p>
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| Components/MyComponent.razor.cs
|
public partial class MyComponent : ComponentBase
{
[Parameter]
public RenderFragment ChildContent { get; set; }
}
|
| Components/MyComponent.razor.css
|
h1 {
color: coral;
}
|
| Pages/Index.razor
|
@page "/"
@using Component.Components
<MyComponent>
test !!!
</MyComponent>
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| Components/MyComponent.razor.cs
|
[Parameter]
public EventCallback<string> Callback { get; set; }
private string description;
private async Task UpdateDescription()
{
await Callback.InvokeAsync(description);
}
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| Pages/Index.razor
|
<MyComponent Callback="MyComponentCallback" />
@code {
void MyComponentCallback(string description)
{
}
}
|
| Components/MyComponent.razor.cs
|
[Parameter]
public string Description { get; set; }
// name of the EventCallback has to be [PropertyName]Changed
[Parameter]
public EventCallback<string> DescriptionChanged { get; set; }
private async Task UpdateDescription()
{
await DescriptionChanged.InvokeAsync(description);
}
|
| Pages/Index.razor
|
@* two ways binding of the component parameter Description with the local field description *@
<MyComponent @bind-Description="description" />
@code {
private string description = "Text";
}
|
Set a value for the component hierarchy from an ancestor component to any number of descendent components.
| Pages/Index.razor
|
@* BtnStyle will be available in MyComponent and all its descendent components *@
<CascadingValue Value="btnStyle" IsFixed="true">
<MyComponent />
</CascadingValue>
@code {
string btnStyle = "btn-success";
}
|
| Components/MyComponent.razor.cs
|
// match between the cascading value and the cascading parameter is made by the type (string) and not by the property name
[CascadingParameter]
public string BtnStyle { get; set; }
|
If the IsFixed value is true (false by default), then receipients receive the initial value but do not set up any subscription to receive updates. In this case, each [CascadingParameter] is lightweight and no more expensive than a regular [Parameter].
So wherever possible, you should use IsFixed="true" on cascaded values. You can do this whenever the value being supplied doesn't change over time.
