How to use Bootstrap modal in Blazor client app?

There is likely a better way to do this, but here's a working example to get you started:

Page:

@page "/modal-test"

<BlazorApp1.Components.Modal @ref="Modal"></BlazorApp1.Components.Modal>

<button @onclick="() => Modal.Open()">Open Modal</button>

@code {
    private BlazorApp1.Components.Modal Modal { get; set; }
}

Component:

<div class="modal @ModalClass" tabindex="-1" role="dialog" style="display:@ModalDisplay">
    <div class="modal-dialog" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title">Modal title</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                <p>Modal body text goes here.</p>
            </div>
            <div class="modal-footer">
                <button type="button" class="btn btn-primary">Save changes</button>
                <button type="button" class="btn btn-secondary" data-dismiss="modal" @onclick="() => Close()">Close</button>
            </div>
        </div>
    </div>
</div>


@if (ShowBackdrop)
{
    <div class="modal-backdrop fade show"></div>
}


@code {


  public Guid Guid = Guid.NewGuid();
    public string ModalDisplay = "none;";
    public string ModalClass = "";
    public bool ShowBackdrop = false;

    public void Open()
    {
        ModalDisplay = "block;";
        ModalClass = "Show";
        ShowBackdrop = true;
        StateHasChanged();
    }

    public void Close()
    {
        ModalDisplay = "none";
        ModalClass = "";
        ShowBackdrop = false;
        StateHasChanged();
    }
}

Another option to go about this, would be to use JSInterop to call $('#modalId').modal()

You could have each version of the component have a unique id by doing something like this: <div id="bootstrap-modal-@Guid" then use the saved ID to call .modal() with jQuery.

Also building on Kyle's answer, you can sustain the bootstrap fade effect if you place a short delay between the display and class adjustments.

@code {

    ...

    public async Task OpenModal()
    {
        ModalDisplay = "block;";
        await Task.Delay(100);//Delay allows bootstrap to perform nice fade animation
        ModalClass = "show";
        StateHasChanged();
    }

    public async Task CloseModal()
    {
        ModalClass = "";
        await Task.Delay(250);
        ModalDisplay = "none;";
        StateHasChanged();
    }
}

I also applied the ModalClass and ModalDisplay variables to the backdrop element too

<div class="modal-backdrop fade @ModalClass" style="display: @ModalDisplay"></div>

I believe bootstrap can better identify the state change that triggers the animation this way

Building on Kyle's answer, this is my first experiment with Blazor: Making the modal dialog component take any markup or component.

Modal.razor

<div class="modal @modalClass" tabindex="-1" role="dialog" style="display:@modalDisplay; overflow-y: auto;">
    <div class="modal-dialog modal-lg" role="document">
        <div class="modal-content">
            <div class="modal-header">
                <h5 class="modal-title">@Title</h5>
                <button type="button" class="close" data-dismiss="modal" aria-label="Close" @onclick="Close">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body">
                @Body
            </div>
            <div class="modal-footer">
                @Footer
            </div>
        </div>
    </div>
</div>

@if (showBackdrop)
{
    <div class="modal-backdrop fade show"></div>
}

@code {
    [Parameter]
    public RenderFragment Title { get; set; }

    [Parameter]
    public RenderFragment Body { get; set; }

    [Parameter]
    public RenderFragment Footer { get; set; }

    private string modalDisplay = "none;";
    private string modalClass = "";
    private bool showBackdrop = false;

    public void Open()
    {
        modalDisplay = "block;";
        modalClass = "show";
        showBackdrop = true;
    }

    public void Close()
    {
        modalDisplay = "none";
        modalClass = "";
        showBackdrop = false;
    }
}

Index.razor

@page "/"

<h1>Hello, world!</h1>

Welcome to your new app.
<button class="btn btn-primary" @onclick="() => modal.Open()">Modal!</button>

<Modal @ref="modal">
    <Title>This is a <em>Title!</em></Title>
    <Body>
        <p>
            Lorem ipsum dolor sit amet, consectetur adipiscing elit. Omnes enim iucundum motum, quo sensus hilaretur.
            <i>Quis istud possit, inquit, negare?</i>
            <mark>Ego vero isti, inquam, permitto.</mark> Duo Reges: constructio interrete.
        </p>
        <FetchData />
        <dl>
            <dt><dfn>Stoici scilicet.</dfn></dt>
            <dd>An hoc usque quaque, aliter in vita?</dd>
            <dt><dfn>Erat enim Polemonis.</dfn></dt>
            <dd>Quod cum accidisset ut alter alterum necopinato videremus, surrexit statim.</dd>
        </dl>
    </Body>
    <Footer>
        <button type="button" class="btn btn-primary">Save changes</button>
        <button type="button" class="btn btn-secondary" data-dismiss="modal" @onclick="() => modal.Close()">Close</button>
    </Footer>
</Modal>

@code {
    private Modal modal { get; set; }
}