Critical Hit Technologies

Unnecessary attributes and layouts on a Xamarin.Forms page can slow down the performance of your app – https://docs.microsoft.com/en-us/xamarin/xamarin-forms/deploy-test/performance. This guidance has been around for a long time, but we wanted to know what kind of impact it really can have.

Putting it to the test

We created two similar ListView layouts. The first layout intentionally violates some guidelines, including having unnecessary StackLayout wrappings and redundant LayoutOptions and Grid attribute declarations. The second layout is a more concise representation of the first layout, achieving the same layout but avoiding the unnecessary elements. The layouts are shown in the screenshots below:

Continue reading “Inefficient Xamarin.Forms Layouts”

A while back, I wrote about how to handle reselecting/retapping of tabs in a Xamarin.Forms TabbedPage (covering iOS and Android in part 1 here and UWP and NavigationPage in part 2 here).  The basic problem is that app designs frequently want to react to a user selecting the already-active tab on a TabbedPage — reselecting, or retapping, the tab.  Sometimes the app might want to pop the navigation stack, or perhaps it would scroll to the top of a ListView.  Whatever the desire, Xamarin.Forms does not make it easy to catch these reselect events.

A lot has happened since the initial solution presented in the above-mentioned posts, for instance Xamarin.Forms has moved from version 2.3 to version 3.6, and tab icons are supported across the three platforms in the sample (iOS, Android, UWP).

If you’re only interested in iOS and Android, there’s nothing new here.  If you need to know how to do this for UWP, read on!

Adding Icons to Tabs

Icons are now supported on tabs on all three of the platforms implemented by this app, just set the Icon property on the immediate children of the TabbedPage. The Image resource must be in the platform-specific projects; shared assembly resources cannot be used for tab Icons.

Unlike iOS and Android, UWP does not support icons on tabs by default. In order to enable tab icons on UWP, the XAML declaration for the TabbedPage needs to be updated:

<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
            xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
            xmlns:windows="clr-namespace:Xamarin.Forms.PlatformConfiguration.WindowsSpecific;assembly=Xamarin.Forms.Core"
            x:Class="TabReselectDemo.MainPage"
            windows:TabbedPage.HeaderIconsEnabled="true">

Continue reading “Tab Retap in Xamarin.Forms, Now With Icons!”

In a previous post, I started methodically working through how LayoutOptions work inside different containers.  In this post, that topic is continued, detailing the interactions between LayoutOptions and Grid.

While LayoutOptions values on child views of Grids do aid in positioning the views, LayoutOptions values do not have the same amount of control over the position of child views within Grids as they do over the position of child views within StackLayouts. This is because a Grid’s RowHeight and ColumnWidth values, function to define each child view’s position and dimensions.

For instance, if a view has its Grid.Row property set to 0, its Grid.Column property set to 0 and its Grid.ColumnSpan property set to 2, the view would be positioned at the top left of the Grid. The height allocated to the view would be the height of the first row, and the width allocated to the view would be the width of the first column plus the width of the second column.
Continue reading “Deep Dive into LayoutOptions in Xamarin.Forms Part 2 (Grids)”

Building on a previous post about seeing how a user interacts with a ListView in Xamarin.Forms, the next question is, “Has the user scrolled to the end?”  This can be useful, for instance, if the user is scrolling through a long feed of data, and only a portion is returned at a time.  When the user reaches the end, the app can automatically download more entries.  My colleague Lazareena and I recently collaborated on a solution for this, and here’s what we came up with.

Let’s start with what we want to see on the Forms side of our app. We’ll add this to our class that inherits from ListView:

public static readonly BindableProperty AtEndOfListProperty =
        BindableProperty.Create(nameof(AtEndOfList), typeof(bool), typeof(MyListView), false);

public bool AtEndOfList
{
    get { return (bool)GetValue(AtEndOfListProperty); }
    set
    {
        SetValue(AtEndOfListProperty, value);
    }
}

Continue reading “Have I Reached the End of my ListView?”