69 lines
3.5 KiB
Markdown
69 lines
3.5 KiB
Markdown
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In the new setup, Windows have WindowHandlers. A WindowHandler is defined as
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``` go
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type WindowHandler interface {
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Event(e Event, c interface{})
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}
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```
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Whenever an event to the window or any control within the window comes in, the handler's `Event()` method is called with the event type and a context-specific value (usually the control that triggered the event) as an argument.
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``` go
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type Event int
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const (
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Close Event = iota
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Clicked
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Checked
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Selected
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Dismissed // for dialogs
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// ...
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CustomEvent = 5000 // arbitrary but high enough
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)
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```
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The argument to `Close` is a pointer to a value that determnes whether to continue the closing of the window or not. The semantics of this value (type, possible values, and default; a special case in Cocoa means there could be three possible values) have yet to be defined.
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The argument to all events `e` such that `Clicked` < `e` < `CustomEvent` is a pointer to the Control (or Dialog; see below) that triggered the event.
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`CustomEvent` represents the first free ID that can be used by the program for whatever it wants, as a substitute for channels. The argument type is program-defened. To trigger a custom event, use the `Window.Send(e, data)` method. `Send()` panics if the event requested is not custom.
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As an example, the timer from `wakeup` might be run on a goroutine:
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``` go
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func (w *MainWin) timerGoroutine() {
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for {
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select {
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case t := <-w.start:
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// set the timer up
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case <-w.timerChan:
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w.win.Send(CustomEvent, nil)
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case <-w.stop:
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// stop the timer
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}
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}
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}
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```
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The underlying OS event handler is not existed until the event handling function returns.
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With the exception of `Window.Create()`, `Window.Open()`, and `Window.Send()`, no objects and methods are safe for concurrent use anymore. They can only be used within an event handler. They can be used within `AreaHandler` methods as well as from the `WindowHandler` method.
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`ui.Go()` no longer takes any arguments. Instead, when initiailization completes, it sends /and waits for the receipt of/ a semaphore value across the `ui.Started` channel, which is immeidately closed after first receipt. Programs should use this flag to know when it is safe to call `Window.Create()`, `Window.Open()`, and `Window.Send()`. A send of a semaphore value to `ui.Stop` will tell `ui.Go()` to return. This return is immediate; there is no opportunity for cleanup.
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The semantics of dialogs will also need changing. It may be (I'm not sure yet) no longer possible to have "application-modal" dialogs. The standard dialog box methods on Window will still exist, but instead of returning a Control, they will return a new type Dialog which can be defined as
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``` go
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type Dialog interface {
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Result() Result
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Selection() interface{} // string for file dialogs; some other type for other dialogs
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// TODO might contain hidden or unexported fields to prevent creating something that's compatible with Dialog but cannot be used as one for the sake of custom Dialogs; see below
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// TODO make it compatible with Control?
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}
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```
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When the dialog is dismissed, a `Dismissed` event will be raised with that dialog as an argument; get the result code by calling `Result()`.
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It might still be possible to have dialog boxes that do not return until the user takes an action and returns the result of that action. I do not know how these will work yet, or what names will be used for either type.
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The Dialog specification above would still allow custom dialogs to be made. In fact, they could be built on top of Window perhaps (or even as a mode of Window), but they would need to be reusable somehow...
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