What is the best way of binding a number of RadioButtons to an enum using MVVM?
The only way I can think of is binding each group box's IsChecked to a property, and in the setter of that property assign a value to an enum in the view model.
You could display the Enum values in a ListBox and provide a special ItemTemplate with a RadioButton plus the name of the Enum. The RadioButton's IsChecked property could then be bound to the ListBoxItem's IsSelected property. Of course, you would have to set the ListBox's SelectionMode to Single.
Related
This tutorial by Apple about SwiftUI uses a dollar sign to bind data, and I‘m having trouble finding more information about this data binding in SwiftUI.
Toggle(isOn: $showFavoritesOnly) {
You use the $ prefix to access a binding to a state variable, or one of its properties.
Is this some sort of inout type parameter? That uses the ampersand to pass it on.
This is very well explained in WWDC 2019 video 415. You are merely looking at one special case of a broad language feature, namely property wrappers.
A property wrapper (such as #State) is actually a way of referring to an instance of a type (usually a struct or enum) with the same name (such as State). The latter provides instructions for turning this instance property into a computed property whose getter and setter are the getter and setter for a certain computed property of itself (its wrappedValue). It also typically holds private storage backing that computed property.
Thus, after the declaration
#State var showFavoritesOnly = true
...showFavoritesOnly is turned into a computed property, with its getter and setter supplied by the State struct. When you set showFavoritesOnly to true, that is routed through the State struct's setter and ends up in a stored property of the State instance.
All of this implies that somewhere there is a State instance associated with your showFavoritesOnly. And there is, but it's hidden from view. Its name, in case you'd like to see that State instance, is _showFavoritesOnly.
Okay, but when you say $showFavoritesOnly, you do not get a State struct; you get a Binding struct. Why? That's because a property wrapper has a mechanism for specifying what the returned value from the $ name should be. In the case of State, it specifies that this value should be its own binding property, which is a Binding (see the docs: https://developer.apple.com/documentation/swiftui/state).
By an amazing coincidence, Toggle's isOn initializer takes a Binding (again, see the docs, https://developer.apple.com/documentation/swiftui/toggle/3232112-init). You could not have set the Toggle's isOn to showFavoritesOnly even if you wanted to! Instead, you set it to the Binding<Bool> supplied by the State instance, so that the Toggle has automatic two-way communication with the State object. The SwiftUI framework enforces its own correct usage; a Toggle can exist only in relation to some binding that acts as the underlying source of truth for its on/off state. And because it's a binding, not a mere Bool, communication works in both directions: when the user taps the switch in the Toggle, the change in value flows "up" to the State variable by way of the binding.
The $ is used in conjunction with property wrappers (previously known as "property delegates").
It's not an operator, but a prefix (thanks #matt!).
For more about property delegates, see this Swift Evolution document.
e.g. in #State var aState = false, State is a property wrapper.
This means that if we write:
aState we're accessing a Bool value
$aState we're accessing a Binding<Bool> value
Different property delegates will generate different values, called "projected values".
This tutorial by Apple about SwiftUI uses a dollar sign to bind data, and I‘m having trouble finding more information about this data binding in SwiftUI.
Toggle(isOn: $showFavoritesOnly) {
You use the $ prefix to access a binding to a state variable, or one of its properties.
Is this some sort of inout type parameter? That uses the ampersand to pass it on.
This is very well explained in WWDC 2019 video 415. You are merely looking at one special case of a broad language feature, namely property wrappers.
A property wrapper (such as #State) is actually a way of referring to an instance of a type (usually a struct or enum) with the same name (such as State). The latter provides instructions for turning this instance property into a computed property whose getter and setter are the getter and setter for a certain computed property of itself (its wrappedValue). It also typically holds private storage backing that computed property.
Thus, after the declaration
#State var showFavoritesOnly = true
...showFavoritesOnly is turned into a computed property, with its getter and setter supplied by the State struct. When you set showFavoritesOnly to true, that is routed through the State struct's setter and ends up in a stored property of the State instance.
All of this implies that somewhere there is a State instance associated with your showFavoritesOnly. And there is, but it's hidden from view. Its name, in case you'd like to see that State instance, is _showFavoritesOnly.
Okay, but when you say $showFavoritesOnly, you do not get a State struct; you get a Binding struct. Why? That's because a property wrapper has a mechanism for specifying what the returned value from the $ name should be. In the case of State, it specifies that this value should be its own binding property, which is a Binding (see the docs: https://developer.apple.com/documentation/swiftui/state).
By an amazing coincidence, Toggle's isOn initializer takes a Binding (again, see the docs, https://developer.apple.com/documentation/swiftui/toggle/3232112-init). You could not have set the Toggle's isOn to showFavoritesOnly even if you wanted to! Instead, you set it to the Binding<Bool> supplied by the State instance, so that the Toggle has automatic two-way communication with the State object. The SwiftUI framework enforces its own correct usage; a Toggle can exist only in relation to some binding that acts as the underlying source of truth for its on/off state. And because it's a binding, not a mere Bool, communication works in both directions: when the user taps the switch in the Toggle, the change in value flows "up" to the State variable by way of the binding.
The $ is used in conjunction with property wrappers (previously known as "property delegates").
It's not an operator, but a prefix (thanks #matt!).
For more about property delegates, see this Swift Evolution document.
e.g. in #State var aState = false, State is a property wrapper.
This means that if we write:
aState we're accessing a Bool value
$aState we're accessing a Binding<Bool> value
Different property delegates will generate different values, called "projected values".
Can we use an AccessGroup name to make visible a column in a ViewModel?
For instance, if we have an AccessGroup called "IsLoggedIn" can we use it in Ocl to set Visible Expression for a column in a ViewModel?
What it would be the Ocl Expression to access the AccessGroup "IsLoggedIn" variable?
Thanks
I'm trying to set the property of a control using another control's property. In my case, I have one <sap.m.Select> and a <sap.m.Input>. The visible of <sap.m.Input> will depend on the selectedItem of the <sap.m.Select>. IMO, there is an available approach using Expression binding in XML View but I don't know how. Any suggestion?
You can use two way binding so that both properties are binding expressions over the same property in the model.
So you can create a JSON model for example and put there a property called selectedItem. The binding of the properties should be: on select selectedItem={mymodel>selectedItem} and on input visible={parts: [{path: "mymodel>selectedItem"}], formatter: function (selectedItem) {<your manipulation>} }.
You can do that with JavaScript and with XML view. In XML view you should reference to a formatter method in the controller.
I want to get an element's property (for instance, value) in WebKitGTK. I can easily get an attribute, and I can also get some properties of some types by using e.g. webkit_dom_html_input_element_get_value, but is there a general way of getting any property of any element which has that property?