The Mvvm-Extensions library provides base implementations of classes, required for WPF application which intends to utilize MVVM pattern. Additionaly, the library provides a few solutions to common problems that arise during GUI development.
PM> Install-Package Mvvm-Extensions -Version 1.4.0
This library provides a few mechanisms that allow to greatly simplify the initial development of WPF application that utilizes MVVM pattern.
PropertyChangedImplementation is a class that provides base implementation of the essential INotifyPropertyChanged interface.
Classes, that inherit PropertyChangedImplementation can invoke PropertyChanged event by calling NotifyPropertyChanged() method in their property setters. Name of the invoking property is pulled automatically.
class RectangleViewModel : PropertyChangedImplementation
{
int width = 0;
int height = 0;
public int Width
{
get
{
return width;
}
set
{
if (width != value)
{
width = value;
NotifyPropertyChanged();
}
}
}
public int Height
{
get
{
return height;
}
set
{
if (height != value)
{
height = value;
NotifyPropertyChanged();
}
}
}
}In addition, the library contains two ways to simplify usage of properties, that are dependant upon other properties in their get accessor.
Lets assume we have three properties in datacontext, all of which are displayed in the view: width, height and area, where width and height are standalone properties and area is a read-only property that returns a product of width and height properties.
In a normal scenario changing the values of width or height properties will not change the displayed value of area property, unless PropertyChanged is explicitly invoked for it.
Properties, marked with DependsOn attribute automatically invoke PropertyChanged event when this event is invoked for one of the properties, specified in attribute parameters.
DependsOn attribute should be used in classes that implement INotifyPropertyChanged and either utilize DependencyWatcher class or inherit PropertyChangedImplementation class.
This attribute allows to automatically invoke PropertyChanged event for properties that lack set accessor or their value depends on other properties.
DependencyWatcher is an alternative class that allows to use the DependsOn attribute when its impossible or not desirable to inherit PropertyChangedImplementation by the viewmodel. The viewmodel must implement INotifyPropertyChanged and provide DependencyWatcher with a method for PropertyChanged event invokation.
The resulting behavior of properties marked by DependsOn attribute is the same between both methods.
DelegateCommand provides the most basic implementation of ICommand interface that can be used immediatelly to invoke viewmodel commands from the views.
private bool runningAutomaticOp = false;
public bool RunningAutomaticOp
{
get
{
return runningAutomaticOp;
}
set
{
if (runningAutomaticOp != value)
{
runningAutomaticOp = value;
NotifyPropertyChanged();
}
}
}
[DependsOn(nameof(RunningAutomaticOp))]
public ICommand RunAutomaticOperationCommand
{
get
{
return new DelegateCommand
{
CanExecuteFunc = () => !RunningAutomaticOp,
CommandAction = (x) => RunAutomaticOp()
};
}
}
private void RunAutomaticOp()
{
// Logic
}<Button Command="{Binding RunAutomaticOperationCommand}" />
CursorState class allows application to change the widndows cursor icon while it remains in the application window. The cursor automatically reverts back to the default icon when CursorState instance is disposed.
The following code is used to create behavior visible on the image above:
Application.Current.Dispatcher.Invoke(async () =>
{
using (new CursorState(Cursors.Wait))
{
await Task.Delay(2000);
}
});
The library contains a number of converters that may be useful for complex UI implementations. The available converters are shown below:
- BooleanToVisibilityConverter
- InvertBooleanConverter
- InvertBooleanToVisibilityConverter
- InvertValueToVisibilityConverter
- MultiBoolAndConverter
- MultiBoolOrConverter
- ValueToVisibilityConverter
Converts bool to System.Windows.Visibility
true converts to Visibility.Visible
false converts to converter parameter (default is Visibility.Collapsed)
Inverts bool value
Converts bool to System.Windows.Visibility
true converts to converter parameter (default is Visibility.Collapsed)
false converts to Visibility.Visible
Converts object to System.Windows.Visibility
null converts to Visibility.Visible
Any object converts to converter parameter (default is Visibility.Collapsed)
Converts bool[] to single bool value by performing logican AND operation on each member
Converts bool[] to single bool value by performing logican OR operation on each member
Converts object to System.Windows.Visibility
Any object converts to Visibility.Visible
null converts to converter parameter (default is Visibility.Collapsed)