Blazor component

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• Framework form controls source code

Basic component

Components/MyComponent.razor

<h1>Test</h1> <p>@ChildContent</p>

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>

Callback event

Components/MyComponent.razor.cs

[Parameter] public EventCallback<string> Callback { get; set; } private string description; private async Task UpdateDescription() { await Callback.InvokeAsync(description); }

Pages/Index.razor

<MyComponent Callback="MyComponentCallback" /> @code { void MyComponentCallback(string description) { } }

Binding with component parameters

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"; }

Cascading values and parameters

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; }

Ensure cascading parameters are fixed

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.

Capture references to components

Component references provide a way to reference a component instance for issuing commands.

Pages/Index.razor

<MyComponent @ref="myComponent" /> <button @onclick="@(() => myComponent.MyMethod())"> Call <code>MyComponent.MyMethod</code> </button> @code { private MyComponent myComponent; }

Attribute splatting and arbitrary parameters

Instead of having multiple parameters, have one parameter of type dictionary to pass multiple attributes.

Components/MyComponent.razor.cs

[Parameter(CaptureUnmatchedValues = true)] public IReadOnlyDictionary<string, object> AdditionalAttributes { get; set; } protected string CssClass { get { var cssClass = string.Empty; if (AdditionalAttributes != null && AdditionalAttributes.TryGetValue("class", out var @class)) { cssClass = Convert.ToString(@class, CultureInfo.InvariantCulture); } return cssClass; } }

Pages/Index.razor

<MyComponent class="myClass"></MyComponent>

Custom components

Input text with clear button

InputTextClear.razor

@inherits InputBase<string> <input @attributes="AdditionalAttributes" class="@CssClass" @bind="CurrentValueAsString" @bind:event="@BindEvent" @ref="Element" /> <span class="oi oi-x" @onclick="Clear"></span>

InputTextClear.razor.cs

public partial class InputTextClear3 : InputBase<string> { public ElementReference Element { get; private set; } protected string BindEvent { get { var bindEvent = "onchange"; if (AdditionalAttributes != null && AdditionalAttributes.TryGetValue("bind-event", out var bindEventAttribute)) { var bindEventAttributeAsString = Convert.ToString(bindEventAttribute, CultureInfo.InvariantCulture); if (bindEventAttributeAsString == "onchange" || bindEventAttributeAsString == "oninput") { bindEvent = bindEventAttributeAsString; } } return bindEvent; } } protected override bool TryParseValueFromString( string value, out string result, out string validationErrorMessage) { result = value; validationErrorMessage = null; return true; } private async Task Clear() { CurrentValue = string.Empty; await Element.FocusAsync(); } }

InputTextClear.razor.css

input { margin-right: -1.5rem; padding-right: 1.5rem; }

<InputTextClear @bind-Value="input" bind-event="oninput" id="id" class="class"></InputTextClear3>