In this example, changes to the Hue, Saturation, and Luminosity properties cause the Color property to change, and changes to the Color property causes the other three properties to change. Private float _hue, _saturation, _luminosity Ĭolor = Color.FromHsla(value, _saturation, _luminosity) Ĭolor = Color.FromHsla(_hue, value, _luminosity) Ĭolor = Color.FromHsla(_hue, _saturation, value) The following example shows the HslViewModel that converts a Color value into Hue, Saturation, and Luminosity values, and back again: using System.ComponentModel Ĭlass HslViewModel: INotifyPropert圜hanged MVVM is often used with two-way data bindings for an interactive view based on an underlying data model. In addition, it’s possible to access individual properties of the DateTime property of the viewmodel by separating the properties with periods: The following screenshot shows the result: The Binding markup extension on the Text property of the Label formats the DateTime property. Alternatively, the code-behind file could instantiate the viewmodel. In this example, ClockViewModel is set to the BindingContext of the ContentPage using property element tags. The following example shows XAML that consumes ClockViewModel: In the previous code example, the OnPropert圜hanged method handles raising the event while automatically determining the property source name: DateTime. NET MAUI attaches a handler to this Propert圜hanged event so it can be notified when a property changes and keep the target updated with the new value. Viewmodels typically implement the INotifyPropert圜hanged interface, which provides the ability for a class to raise the Propert圜hanged event whenever one of its properties changes. Propert圜hanged?.Invoke(this, new Propert圜hangedEventArgs(name)) Public void OnPropert圜hanged( string name = "") => Null, TimeSpan.Zero, TimeSpan.FromSeconds(1)) _timer = new Timer(new TimerCallback((s) => this.DateTime = DateTime.Now), Update the DateTime property every second. OnPropert圜hanged() // reports this property Public event Propert圜hangedEventHandler Propert圜hanged The following example shows a viewmodel for a clock, with a single property named DateTime that's updated every second: using System.ComponentModel Ĭlass ClockViewModel: INotifyPropert圜hanged In simple examples of MVVM, such as those shown here, often there is no model at all, and the pattern involves just a view and viewmodel linked with data bindings. However, often you tailor the types exposed by the viewmodel to the types associated with the UI. In MVVM, a model is ignorant of the viewmodel, and a viewmodel is ignorant of the view. The view is often a XAML file that references properties defined in the viewmodel through data bindings. When thinking in terms of MVVM, the model and viewmodel are classes written entirely in code. NET MAUI apps when data binding from properties between visual objects and the underlying data. The MVVM pattern is a natural choice for. However, the problem is that the date and time are set once when the page is constructed and initialized, and never change.Ī XAML page can display a clock that always shows the current time, but it requires additional code. This means that all the children of the StackLayout have the same BindingContext, and they can contain bindings to properties of that object: When you set the BindingContext on an element, it is inherited by all the children of that element. In this example, the retrieved DateTime value is set as the BindingContext on a StackLayout. The following example uses the x:Static markup extension to obtain the current date and time from the static DateTime.Now property in the System namespace: In XAML markup extensions you saw how to define a new XML namespace declaration to allow a XAML file to reference classes in other assemblies. NET MAUI's binding engine bringing the updates to the UI thread. When using MVVM this enables you to update data-bound viewmodel properties from any thread, with. NET Multi-platform App UI (.NET MAUI) marshals binding updates to the UI thread.
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