07-DialogService

Dialog Service

The new Prism Dialog Service is designed to provide you a minimalistic framework that you can build on to provide richly styled dialogs that match the look and feel of your app.

Samples	Selector Dialog	Tap to close

YouTube Tutorials

Getting Started:

Dialog View

Let's start with the view for our dialog.

<ContentView xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:prism="http://prismlibrary.com"
    prism:DialogLayout.RelativeWidthRequest="0.75"
    ...>

    <!-- The View -->

</ContentView>

Dialog ViewModel

Dialog view's ViewModel implements IDialogAware

public class TermsDialogViewModel : BindableBase, IDialogAware
{
    public TermsDialogViewModel()
    {
        Title = "Terms and Conditions";
        SubmitCommand = new DelegateCommand(OnSubmitTapped)
            .ObservesCanExecute(() => CanContinue);
        CancelCommand = new DelegateCommand(OnCancelTapped);
    }

    public DelegateCommand SubmitCommand { get; }
    public DelegateCommand CancelCommand { get; }

    // IDialogAware
    public event Action<IDialogParameters> RequestClose;
    public bool CanCloseDialog() { ... };
    public void OnDialogClosed() { }
    public void OnDialogOpened(IDialogParameters parameters) { }
}

Dialog Registration

Register your dialogs to the container in RegisterTypes() of the App class

containerRegistry.RegisterDialog<TermsDialog>();
containerRegistry.RegisterDialog<LockingDialog>();
containerRegistry.RegisterDialog<NameDialog>();
containerRegistry.RegisterDialog<ContactSelectorDialog>();

Usage

private readonly IDialogService _dialogService;
public SelectorPageViewModel(IDialogService dialogService)
{
    _dialogService = dialogService;
}

Show the dialog,

_dialogService.ShowDialog("LockingDialog");

Show the dialog and pass in DialogParameters,

// using Query string
_dialogService.ShowDialog("LockingDialog?Question=Can navigate away?");

// using DialogParameters
_dialogService.ShowDialog("LockingDialog", new DialogParameters
{
    { "Question", "Can navigate away?" }
});

Show the dialog and handle callback,

_dialogService.ShowDialog("TermsDialog", new DialogParameters(), HandleCallback);

private void HandleCallback(IDialogResult result)
{...}

Extensions

DialogService can be extended to meet the needs. In this sample, the DialogService has a couple of async extension methods and a generic extension.

ShowDialogAsync

This extensions allows showing of the dialog to be awaited.

public static Task<IDialogResult> ShowDialogAsync(this IDialogService dialogService,
    string name,
    IDialogParameters parameters)
{
    var tcs = new TaskCompletionSource<IDialogResult>();

    try
    {
        dialogService.ShowDialog(name, parameters, (result) => {
            if (result.Exception != null)
            {
                tcs.SetException(result.Exception);
                return;
            }
            tcs.SetResult(result);
        });
    }
    catch (Exception ex)
    {
        tcs.SetException(ex);
    }
    return tcs.Task;
}

usage,

var r = await _dialogService.ShowDialogAsync("NameDialog");
return r.Parameters.GetValue<string>("Name");

ShowDialogAsync<T>

This extension shows the dialog and expects a parameter with the name matching the Type name.

public static Task<T> ShowDialogAsync<T>(this IDialogService dialogService,
            string name)
{
    var tcs = new TaskCompletionSource<T>();

    try
    {
        dialogService.ShowDialog(name, (result) =>
        {
            if (result.Exception != null)
            {
                tcs.SetException(result.Exception);
                return;
            }
            tcs.SetResult(result.Parameters.GetValue<T>(typeof(T).Name));
        });
    }
    catch (Exception ex)
    {
        tcs.SetException(ex);
    }
    return tcs.Task;
}

usage,

var contact = await _dialogService.ShowDialogAsync<Contact>("ContactSelectorDialog");

Note: These extensions are for reference purposes only. Use these techniques to make extensions that fit your needs.