'How to use Bootstrap modal in Blazor client app?

I am trying to show bootstrap modal then bind its buttons. But I cannot pass the first step showing the modal. I am using Blazor client template of .net core 3.1. I have a page named Modal.razor which contains the bootstrap modal I found from getbootstrap.com.

@if (Show)
{
    <div class="modal" tabindex="-1" role="dialog">
        <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">Close</button>
                </div>
            </div>
        </div>
    </div>
}
@code {
    [Parameter]
    public bool Show { get; set; } = false;
}

An I called the modal in the index.razor file

@page "/"

<button @onclick="(()=>switchModal=!switchModal)">Switch Modal</button>

<Modal Show="switchModal"/>

@code{
    bool switchModal = false;
}

You might say StateHasChanged should be called here. But even if I copy and paste the modal code in the index.razor, I won't see anything.

Solution 1:^[1]

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.

Solution 2:^[2]

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; }
}

Solution 3:^[3]

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

Solution 4:^[4]

With Kyle solution my Dialog do not close when i click on the backdrop.

I saw that it is a problem of z-index: the modal div has a z-index of 1050, and the backdrop div has 1040, in this way i was not able to click my backdrop.

I have moved the backdrop inside the dialog div and added to the modal-dialog div z-index > 1040 (ES: 1055)

I also added data-dismiss="modal" @onclick="() => Close()" to the backdrop div and now it works as well as the "Close" button.

<div class="modal @ModalClass" tabindex="-1" role="dialog" style="display:@ModalDisplay">

    <div class="modal-dialog" role="document" style="z-index:1055">
       ...
    </div>    

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

</div>

Solution 5:^[5]

for backdrop shadow only add fade class:

<div class="modal fade @ModalClass" tabindex="-1" role="dialog" 
     style="display:@ModalDisplay">

Solution 6:^[6]

Kyle's components work well but does anyone know how to add draggable and resizable features to a bootstrap modal using the jqueryUi draggable()/resizeable() functions?

I have this link to a pure javascript solution: DRAG AND RESIZE BOOTSTRAP MODAL that essentially calls the resizeable and draggable functions on the modal divs

<script src="https://code.jquery.com/ui/1.11.3/jquery-ui.min.js"></script>
<script type="text/javascript">
    $('.modal-content').resizable({
        //alsoResize: ".modal-dialog",
        minHeight: 300,
        minWidth: 300
    });
    $('.modal-dialog').draggable();
</script>

I've tried adding this script to my _Host.cshtml page but it has no effect. Any advice on how to do this would be gratefully received...

David

Updated with answer

The answer is to explicitly call a javascript function in the OnAfterRenderAsync override to apply the JQuery UI functions to the modal divs.

E.g.

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        await jsRuntime.InvokeVoidAsync("setModalDraggableAndResizable");
        await base.OnAfterRenderAsync(firstRender);
    }

where setModalDraggableAndResizable is a javascript function in the _Hosts.cshtml:

    <script src="https://code.jquery.com/ui/1.11.3/jquery-ui.min.js"></script>
    <script type="text/javascript">
        function setModalDraggableAndResizable() {
            $('.modal-content').resizable({
                //alsoResize: ".modal-dialog",
                minHeight: 300,
                minWidth: 300
            });
            $('.modal-dialog').draggable();
        }
    </script>

And the modal is now draggable and resizable...

Modal example image

Solution 7:^[7]

As an alternative you can use Bootstrap Blazor which is a open-source and very nice implementation of bootstrap integrated with blazor.

Solution 8:^[8]

Update: I've converted this answer into a service which can be found here.

I adjusted Kyles and grammophones answers to support our beloved Alert, Prompt, and Confirm from both C# and JavaScript. Tested in the lastest Blazor Server release with Bootstrap 5.

ProjectName.Components.Modal.razor

@using Microsoft.JSInterop
<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 w-100 text-center" style="padding-left:31px">@Title</h5>
                <button type="button" class="close border-0 bg-white" data-dismiss="modal" aria-label="Close"  @onclick="() => Close(true)">
                    <span aria-hidden="true">&times;</span>
                </button>
            </div>
            <div class="modal-body mx-auto text-center">
                @Body
                @if (MType == ModalType.Prompt){ 
                    <input type="text" class="form-control text-center my-2" @bind-value="PromptValue" style="max-width:400px"></input> 
                }
            </div>
            <div class="modal-footer justify-content-center">
                @if (MType == ModalType.Prompt || MType == ModalType.Confirm)
                {
                    <button type="button" class="btn btn-secondary" data-dismiss="modal" @onclick="() => Close(false)">OK</button>
                    <button type="button" class="btn btn-secondary" data-dismiss="modal" @onclick="() => Close(true)">Cancel</button>
                }
                else
                {
                    <button type="button" class="btn btn-secondary" data-dismiss="modal" @onclick="() => Close(false)">Close</button>
                }
            </div>
        </div>
    </div>
</div>

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

@code {

    [Inject] IJSRuntime JS { get; set; }

    public enum ModalType
    {
        Alert,
        Prompt,
        Confirm
    }

    /// <summary>
    /// (Optional) We can setup an instance of this .net object to call directly from JavaScript. See JavaScript Usage section.
    /// </summary>
    /// <returns></returns>
    protected override async Task OnInitializedAsync()
    {
        JS.InvokeVoidAsync("MODAL.SetDotnetReference", DotNetObjectReference.Create(this));
    }

    private string Title { get; set; }
    private string Body { get; set; }


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


    private string PromptValue { get; set; }
    private bool ConfirmValue { get; set; }
    private ModalType MType { get; set; }



    private List<string> MsgIds = new List<string>();
    [JSInvokable("Show")]
    public async Task<dynamic> Show(ModalType mType, string title, string body)
    {
        // The JavaScript call MODAL.DotNetReference.invokeMethodAsync is non-blocking
        // This means multiple calls to show the modal using invokeMethodAsync will only show the modal once.
        // We can solve this by making sure each message waits in line.

        string msgId = Guid.NewGuid().ToString();

        if (!MsgIds.Contains(msgId))
            MsgIds.Add(msgId);

        // If multiple messages are being processed, wait for this msgs turn.
        while (MsgIds.Count > 1 && MsgIds.IndexOf(msgId) != 0)
            await Task.Delay(250);

        Title = title;
        Body = body;
        ModalDisplay = "block;";
        ModalClass = "Show";
        MType = mType;
        ShowBackdrop = true;
        StateHasChanged();

        while (ShowBackdrop)
            await Task.Delay(250);

         switch(mType)
        {
            default:
            case ModalType.Alert:
                MsgIds.Remove(msgId);
                return string.Empty;
            case ModalType.Confirm:
                bool confirmResponse = ConfirmValue;
                MsgIds.Remove(msgId);
                return confirmResponse;
            case ModalType.Prompt:
                string promptResponse = PromptValue;
                MsgIds.Remove(msgId);
                return promptResponse;
        }

    }

    private void Close(bool isCancel)
    {
        // Determine returned values.
        PromptValue = isCancel ? string.Empty : PromptValue;
        ConfirmValue = isCancel ? false : true;

        ModalDisplay = "none";
        ModalClass = "";
        ShowBackdrop = false;
        StateHasChanged();
    }
}

Markup Usage

<Modal @ref="Modal"></Modal>
<button @onclick='() => Modal.Show(Modal.ModalType.Alert, "Title goes here","Body goes here")'>Open Modal</button>

Code Usage

if (await Modal.Show(Modal.ModalType.Confirm,"Save Settings", "Are you sure you want to save settings?"))
{
    string fileName = await Modal.Show(Modal.ModalType.Prompt, "File Name", "Please enter a filename");
    if (!string.IsNullOrEmpty(fileName))
        await Modal.Show(Modal.ModalType.Alert, "File Saved", $"File Saved as {fileName}");
}

JavaScript Usage

With promise support we can get a response from Prompt and Confirm right from JavaScript. To avoid declaring our Modal as static we need to setup a DotNetReference.

// Defined somewhere globally
var MODAL = {};
MODAL.DotNetReference = null;
MODAL.SetDotnetReference = function (pDotNetReference) {
    MODAL.DotNetReference = pDotNetReference;
};
MODAL.MType = {
    Alert: 0,
    Prompt:1,
    Confirm: 2,
};

// Called from wherever
MODAL.DotNetReference.invokeMethodAsync('Show', MODAL.MType.Prompt, `Title goes here`, `Body goes here`)
.then(data => {
    console.log(`Prompt Response`, data);
});

JavaScript Note: Polyfil recommended for promise support in older browsers

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1
Solution 2	grammophone
Solution 3	Daniel
Solution 4	Daniele Ranaldi
Solution 5	Ali Belyani
Solution 6
Solution 7	Kaveh Naseri
Solution 8

'How to use Bootstrap modal in Blazor client app?

Solution 1:[1]

Solution 2:[2]

Modal.razor

Index.razor

Solution 3:[3]

Solution 4:[4]

Solution 5:[5]

Solution 6:[6]

Solution 7:[7]

Solution 8:[8]