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Håvard Moås edited this page Mar 28, 2020 · 42 revisions

Description

A sheet appears as a card that partially covers the page and can be dragged in a vertical direction to show more content. The page's content is visible behind the sheet to help people to remember the context they suspended when they opened the sheet.

Getting started

A sheet needs to live inside of a ModalityLayout. The ModalityLayout will provide an overlay that is disabled until the modal component closes. It will also add the possibility of tapping the overlay to close the modal component. The ModalityLayout should be placed at the root of your page for the best user experience.

In your XAML page, add the following:

<Contentpage 
   ...
   xmlns:dxui="http://dips.xamarin.ui.com"
   ... >
<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior>
        <!-- sheet content goes here -->
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

👉 All pictures and GIFs are taken from a android simulator, but the look and feel of this component is the same for android / ios devices.

👉 Samples can be found here

👉 A small demonstration of Sheet was visible at .Net Conf:2020

Open a sheet

To open a sheet, set the IsOpen property to True.

👉 This is a bindable property and should be bound to a view model property that changes when people tap a view element inside of the page.

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True">
        <!-- sheet content goes here -->
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

Screenshot_1579676014

Adding content to the sheet

Content of the sheet can be set by setting the SheetContent property, which is the default ContentProperty of the behavior. This means that you can add the content directly inside of the SheetBehavior tags.

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True">
            <!-- sheet content goes here -->
            <Label Text="This is the sheet content"/>
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

Screenshot_1579675865

Sheet alignment

The sheet's alignment can be changed by setting the Alignment property.

👉 Default is Bottom

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True"
                            Alignment="Top" >
        <!-- sheet content goes here -->
        <Label Text="This is the sheet content"/>
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

Screenshot_1579675953

Setting the position of the sheet

The default behavior of the sheet is to take as much space as it needs when it opens. One exception to that is if a MinPosition is set. The sheet will either take as much space as it needs, or set the position to a MinPosition if the position from the content size is smaller than that.

Another exception is if the consumer of the API has set the Position property. This property has to have values between 0.0 - 1.0 (0% - 100% of the screen).

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True"
                            Position="0.5"
                            MinPosition="0.4"
                            MaxPosition="0.7">
            <!-- sheet content goes here -->
            <Label Text="This is the sheet content"/>
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

👉 This property is a two-way binding, and the consumer can use this to get notified for changes to the sheet.

👉 Setting MinPosition / MaxPosition will prevent people from dragging the sheet below / above the threshold. In this example the sheet is placed at 50% of the screen and people can not drag the sheet below 40% or above 70% of the screen.

Screenshot_1579698962

Dragging the sheet

The sheet can be dragged by setting the IsDraggable to True.

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True"
                            IsDraggable="True" >
        <!-- sheet content goes here -->
        <Label Text="This is the sheet content"/>
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

sheet_draggable

sheet_draggable_top

Closing the sheet from sheet content

The content of the sheet might have some kind of view element that should close the sheet. This can be achieved by using our Modality.CloseOnClick attached property on the view element.

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True">
            <!-- sheet content goes here -->
            <StackLayout>
                <Label Text="This is the sheet content" />
                <Button Text="Press to close"
                        dxui:Modality.CloseOnClick="True" />
            </StackLayout>
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

👉 This attached property can be attached to any type of Xamarin.Forms.View element.

sheet_onclose

Prevent auto closing

The sheet automatically closes when people drag it below 0.05 % of the ModalityLayout.

sheet_close_whendraggedout_android

If you want to prevent this, you can set MinPosition to a percentage that is bigger than 0.05.

sheet_close_whendraggedout_withmin_android

Changing colors

The background of the sheet and the drag-handle's color can be changed from it's default colors.

<dxui:ModalityLayout>
    <dxui:ModalityLayout.Behaviors>
        <dxui:SheetBehavior IsOpen="True"
                            IsDraggable="True"
                            BackgroundColor="#323E40"
                            HandleColor="#D94D1A">
            <!-- sheet content goes here -->
        </dxui:SheetBehavior>
    </dxui:ModalityLayout.Behaviors>
    <!-- page content goes here -->
</dxui:ModalityLayout>

Screenshot_1579677114

Setting BindingContext for the content

The content of the sheet might need it's own BindingContext. This is natural when working with the MVVM pattern.

In the following examples, we have added a SheetPageViewModel that should provide an instance of InsideSheetViewModel.

  • SheetPageViewModel should be the BindingContext of the entire page.
  • InsideSheetViewModel should be the BindingContext of the sheet's content.

xaml:

<ContentPage>
    <ContentPage.BindingContext>
        <local:SheetPageViewModel />
    </ContentPage.BindingContext>
    <dxui:ModalityLayout>
        <dxui:ModalityLayout.Behaviors>
            <dxui:SheetBehavior IsOpen="True"
                                IsDraggable="True"
                                BindingContextFactory="{Binding SheetViewModelFactory}">
                <!-- sheet content goes here -->
                <Label Text="{Binding Title}" /> <!-- "Sheet Title" is the value here -->
            </dxui:SheetBehavior>
        </dxui:ModalityLayout.Behaviors>
        <!-- page content goes here -->
    </dxui:ModalityLayout>
</ContentPage>

SheetPageViewModel:

public class SheetPageViewModel : INotifyPropertyChanged
{
    public Func<object> SheetViewModelFactory => () => new InsideSheetViewModel();

    public event PropertyChangedEventHandler PropertyChanged;
}

InsideSheetViewModel:

 public class InsideSheetViewModel : INotifyPropertyChanged
    {
        public string Title => "Sheet Title";

        public event PropertyChangedEventHandler PropertyChanged;
    }

iOS demo

Here is a small demonstration of the sheet running on an iOS simulator with our samples code.

sheet_ios

Properties

Property Explanation Remarks default value
Alignment Determines the position of the sheet when it appears. Bottom
VerticalContentAlignment Determines how the content of the sheet should align. Fit
SheetContent The content of the sheet. BindingContextFactory to set the binding context when the sheet opens null
BindingContextFactory Used to set the binding context of the content of the sheet when the sheet opens. If this is not set, the BindingContext of the ModalityLayout will be used. null
BackgroundColor Determines the color of the background of the sheet. Color.White
HandleColor Determines the color of the handle in the sheet. ColorPalette.QuinaryAir
HasShadow Determines if the sheet should have shadow. This only works for iOS. false
IsDraggable Determines if the sheet should be drag-able or not. false
IsOpen Determines if the sheet should be visible or not. false
MaxPosition Determines the maximum position of the sheet when it is visible. This will affect the size of the sheet if Position is set to 0.0. This will affect the people that are dragging the sheet. The value have to be between 0.0 and 1.0 (percentage of the screen) 1.0
MinPosition Determines the minimum position of the sheet when it is visible. This will affect the size of the sheet if Position is set to 0.0. This will affect the people that are dragging the sheet. The value have to be between 0.0 and 1.0 (percentage of the screen) 0.1
OnOpen Event that gets raised when the sheet has completed it's animation and is open.
OnOpenCommand Command that executes when the sheet has completed it's animation and is open null
OnOpenCommandParameter The parameter to pass to theOnOpenCommand null
OnClose Event that gets raised when the sheet has completed it's animation and is closed.
OnCloseCommand TCommand that executes when the sheet has completed it's animation and is closed null
OnCloseCommandParameter The parameter to pass to the OnCloseCommand null
OnBeforeClose Event that gets raised before the sheet start it's animation when closing
OnBeforeCloseCommand Command that execute before the sheet start it's animation when closing. null
OnBeforeCloseCommandParameter The parameter to pass to OnBeforeCloseCommand null
OnBeforeOpen Event that gets raised when the sheet is about to start it's animation to open.
OnBeforeOpenCommand Command that execute when the sheet is about to start it's animation to open. null
OnBeforeOpenCommandParameter Parameter to pass to OnBeforeOpenCommand null
OnBeforeOpenCommandParameter Parameter to pass to OnBeforeOpenCommand null
OnPositionChanged Event that gets raised when the sheet has changed it's position. null
OnPositionChangedCommand A command that executes when the position of the sheet changes. The command parameter will be the new positional value, same as Position null
CloseOnOverlayTapped Determines if the modality component should close when the overlay is tapped. true

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