[Spec] TabView

TabView

We can have tabs using Shell. However, what happens if we want to have nested tabs within a specific section (Example: Grid)?, what if we want to fully customize each tab?. In these cases, we would need a Custom Renderer so far…

The TabView is a way to display a set of tabs and their respective content. TabView is useful for displaying several content while giving a user the capability to customize mostly everything.

NOTE: TabView is a cross-platform view that takes over when native tabs hit their limits, such as positioning with layouts, styling, and non-uniform styling like a raised button.

API

Next, a list with the TabView properties, events and visualstates.

Properties

TabView Properties

Property	Type	Description
TabItemsSource	IEnumerable	A collection used to generate the TabView’s tab items.
TabViewItemDataTemplate	DataTemplate	the template the Tab View uses to generate tab items’ header.
TabContentDataTemplate	DataTemplate	The template the Tab View uses to generate tab items’ content.
IsCyclical	Bool	Enable or disable cyclical tabs navigation.
IsLazy	Bool	Enable or disable lazy tabs loading.
SelectedIndex	Int	Gets or sets the currently selected tab. Default is 0.
TabStripPlacement	TabStripPlacement	The TabStrip placement (top or bottom).
TabStripBackground	Brush	The TabStrip background.
TabIndicatorBrush	Brush	The TabIndicator background.
TabIndicatorHeight	double	The TabIndicator height.
TabIndicatorWidth	double	The TabIndicator width.
TabIndicatorPlacement	TabIndicatorPlacement
TabIndicatorView	View	The TabIndicator content.
TabContentBackground	Brush	The tab content background.
TabContentHeight	Double	The tab content height.
TabStripHeight	Double	The TabStrip height.
TabContentHeight	Double	The tab content height.
HasTabStripShadow	Bool	Show or hide the TabStrip shadow effect.
IsTabTransitionEnabled	Bool	Enable or disable the transition between tabs.
IsSwipeEnabled	Bool	Enable or disable the swipe gesture.

TabViewItem Properties

Property	Type	Description
Text	String	The text of the tab.
TextColor	Color	The text color of the tab.
TextColorSelected	Color	The text color of the selected tab.
FontSize	FontSize	The font size used in the tab text.
FontSizeSelected	FontSize	The font size used in the selected tab.
FontFamily	String	The font family used in the tab.
FontFamilySelected	String	The font family used in the selected tab.
FontAttributes	FontAttributes	The font attributes used in the tab.
FontAttributesSelected	FontAttributes	The font attributes used in the selected tab.
Icon	ImageSource	The icon of the tab.
IconSelected	ImageSource	The ImageSource used as icon in the selected tab.
Content	View	The content of the tab. Is View, can use anything as content.
BadgeText	Bool	The badge text used in the tab.
BadgeTextColor	Color	The badge text color used in the tab.
BadgeTextColorSelected	Color	The badge text color used in the selected tab.
BadgeBackgroundColor	Color	The badge color used in the tab.
BadgeBackgroundColorSelected	Color	The badge color used in the selected tab.
IsSelected	Bool	a bool that indicate if the tab is selected or not.
TapCommand	ICommand	Command that is executed when the user tap a tab.
TapCommandParameter	object	The tap command parameter.

Events

TabView Events

Event	Description
SelectionChanged	Event that is raised when the selected tab changed.
Scrolled	Event that is raised when is swiping between tabs.

TabViewItem Events

Event	Description
TabTapped	Event that is raised when the user tap a tab.

VisualStates

The Visual State Manager (VSM) provides a structured way to make visual changes to the user interface from code. The VSM introduces the concept of visual states. TabView can have several different visual appearances depending on its underlying state.

TabView have four specific VisualStates:

• CurrentTabVisualState
• NextTabVisualState
• PreviousTabVisualState
• DefaultTabVisualState

Scenarios

Let’s see some samples covering common scenarios.

Basic Tabs

Let’s see a basic example:

<TabView 
    TabStripPlacement="Bottom"
    TabStripBackgroundColor="Blue">
    <TabViewItem
        Icon="triangle.png"
        Text="Tab 1">
        <Grid 
            BackgroundColor="Gray">
            <Label
                HorizontalOptions="Center"
                VerticalOptions="Center"
                Text="TabContent1" />
        </Grid>
    </TabViewItem>
    <TabViewItem
        Icon="circle.png"
        Text="Tab 2">
        <Grid>
            <Label    
                HorizontalOptions="Center"
                VerticalOptions="Center"
                Text="TabContent2" />
        </Grid>
    </TabViewItem>
</TabView>

TabItemsSource

Using TabItemsSource (dynamic tabs):

<TabView
    TabItemsSource="{Binding Monkeys}"
    TabViewItemDataTemplate="{StaticResource TabViewItemTemplate}"
    TabContentDataTemplate="{StaticResource TabContentTemplate}" />

Custom Tabs

The appearance of each tab can be customized:

<ControlTemplate
    x:Key="TabItemTemplate">
    <Grid>
    ...
    </Grid>
</ControlTemplate>

<TabView>
    <TabViewItem
        Text="Tab 1"
        ControlTemplate="{StaticResource TabItemTemplate}">
    </TabViewItem>
</TabView>

Cyclical Tabs

Do you want to navigate between the tabs cyclically?

<TabView
    IsCyclical="True">
    ...
</TabView>

Lazy Loading

Lazy tab loading:

<TabView
    IsLazy="True">
    ...
</TabView>

Tab Transitions and TabViewItem animations

Can use Xamarin.Forms animations to customize the transition between each tab, animate the tab when appears or disappears, or even animate the badge when appears or disappears.

<TabView>
    <TabView.TabTransition>
        <local:CustomTabTransition />
    </TabView.TabTransition>
    <TabViewItem
        Text="Tab 1">      
            <TabViewItem.TabAnimation>
                <local:CustomTabViewItemAnimation />
            </TabViewItem.TabAnimation>
        <Grid 
            BackgroundColor="LawnGreen">
            <Label
                HorizontalOptions="Center"
                VerticalOptions="Center"
                Text="TabContent1" />
        </Grid>
    </TabViewItem>
    ...
</TabView>

Using VisualStates

Can use different visual states to customize the current tab, the next tab, etc.

<Grid>
    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup x:Name="TabViewStates">
            <VisualState x:Name="CurrentTab">
                <VisualState.Setters>
                    <Setter Property="Opacity" Value="1" />
                </VisualState.Setters>
            </VisualState>
            <VisualState x:Name="PreviousTab">
                <VisualState.Setters>
                    <Setter Property="Opacity" Value="0.7" />
                </VisualState.Setters>
            </VisualState>
            <VisualState x:Name="NextTab">
                <VisualState.Setters>
                    <Setter Property="Opacity" Value="0.7" />
                </VisualState.Setters>
            </VisualState>
            <VisualState x:Name="DefaultTab">
                <VisualState.Setters>
                    <Setter Property="Opacity" Value="0.9" />
                </VisualState.Setters>
            </VisualState>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>
    <Label Text="{Binding Index}" HorizontalOptions="Center" VerticalOptions="End" />
</Grid>

Create Tabs using C#

You can use XAML or C# to create the UI in Xamarin.Forms. Let’s see how we would create tabs using C#.

var tabView = new Tabs
{
    TabStripPlacement = TabStripPlacement.Bottom,
    TabStripBackgroundColor = Color.Blue,
    TabStripHeight = 60,
    TabIndicatorColor = Color.Yellow,
    TabContentBackgroundColor = Color.Yellow
};

var tabViewItem1 = new TabViewItem
{
    Icon = "triangle.png",
    Text = "Tab 1",
    TextColor = Color.White,
    TextColorSelected = Color.Yellow,
};

var tabViewItem1Content = new Grid
{
    BackgroundColor = Color.Gray
};

var label1 = new Label
{
    HorizontalOptions = LayoutOptions.Center,
    VerticalOptions = LayoutOptions.Center,
    Text = "TabContent1"
};

tabViewItem1Content.Children.Add(label1);

tabViewItem1.Content = tabViewItem1Content;

tabView.TabItems.Add(tabViewItem1);

var tabViewItem2 = new TabViewItem
{
    Icon = "circle.png",
    Text = "Tab 2",
    TextColor = Color.White,
    TextColorSelected = Color.Yellow
};

var tabViewItem2Content = new Grid
{
    BackgroundColor = Color.OrangeRed
};

var label2 = new Label
{
    HorizontalOptions = LayoutOptions.Center,
    VerticalOptions = LayoutOptions.Center,
    Text = "TabContent2"
};

tabViewItem2Content.Children.Add(label2);

tabViewItem2.Content = tabViewItem2Content;

tabView.TabItems.Add(tabViewItem2);

Using Styles

Can customize the appearance of the tab content, tab strip, tab item, etc. using XAML styles or CSS.

Using XAML:

<Style
    x:Key="TabItemStyle"
    TargetType="TabViewItem">
    <Setter
        Property="FontSize"
        Value="12" />
    <Setter
        Property="TextColor"
        Value="#979797" />
</Style>

Using CSS:

.customTabItem {
    font-size: medium;
    text-color: red;
}

Difficulty : Medium

More information

Based on https://github.com/xamarin/Xamarin.Forms/issues/10773

[MhAllan]

@irongut , Thanks for the note. I think those are wrong design as well. There shouldn’t be something like a BadgeText.

If we think of a framework that can meet future requirements we shouldn’t limit developers with types like String or ImageSource. If do so then we will soon get issues like this: Make Badge Corner Rounded, Made Badge Bigger, Smaller, Shadow, Left to the Icon, Up, Down, Right, in front of the icon, behind the icon, Animated … etc. And people will get frustrated they can’t customise it easily. Writing this, I am currently making a notification badge that will rotate around X axis twice before it settles. see how weird customisation can be?

[Inrego]

I agree that the TabViewItem as a whole should more or less just have a ContentView where we can put whatever view we want inside the tab items. The current of doing it, limits us to implementing tab views in the way that you envisioned them, not how we want them. If you want an “easy-to-use” tab view which has a default look, you can just make a SimpleTabItemView class, which people can use as the view for their tab items, while allowing us to implement our own look and feel via our own custom views.