Add command support for actionable controls

[Tom Schindl]

Hi,

I see where you are coming from but IMHO JavaFX should focus on being a
Graphic and UI-Toolkit and not leak any patterns into the core API.

These are just by 2 cents so other might have another opinion.

Tom

On 21.01.20 20:59, Michael Strauß wrote:
> 1. Abstract:
> Controls that are derived from ButtonBase generally represent an operation
> that is triggered by the control.
> In many cases, the control also reflects whether the operation can
> currently be invoked (i.e. whether the control is enabled or disabled), or
> whether the operation is currently running.
> Software patterns like MVVM often encapsulate this behavior for the purpose
> of decoupling business logic from UI code.
> 
> 
> 2. Implementation:
> I propose adding the following interface that represents the entirety of
> such an operation:
> 
> interface Command<T> {
>     ReadOnlyBooleanProperty canExecuteProperty();
>     ReadOnlyBooleanProperty executingProperty();
>     void execute();
>     void execute(T parameter);
> }
> 
> An application's business logic can expose operations as implementations of
> the Command interface, and define the conditions when the operation can be
> executed.
> 
> Additionally, ButtonBase should be extended by adding the following two
> properties:
> 
> /**
>  * The button's command, which is invoked whenever the button is fired.
>  * If a command is set on the button, {@link Node#disableProperty()} is
> automatically
>  * bound to {@link Command#canExecuteProperty()}. Any previous binding is
> removed.
>  */
> ObjectProperty<Command<?>> commandProperty();
> 
> /**
>  * The button's command parameter.
>  * When the command is invoked, this parameter will be passed to the
> command implementation.
>  */
> ObjectProperty<Object> commandParameterProperty();
> 
> These two properties are lazily instantiated to prevent allocations if an
> application doesn't use commands.
> In general, Commands are an opt-in feature, so existing code that makes no
> use of commands is not impacted.
> 
> The command is invoked whenever the control fires an ActionEvent. This can
> be achieved by overriding Node.fireEvent(Event) in ButtonBase and checking
> for the presence of an ActionEvent.
> 
> I can provide a PR with an implementation of this feature.
> 
> Michael
> 

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Tom Schindl, CTO
BestSolution.at EDV Systemhaus GmbH
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