UXControl

UXControl is the base of everything clickable. It adds a title and an action to UXView, and its design centres on one field:

callback action void(UXControl* sender);      // (receiver, code) — and the receiver auto-zeroes

#use <UXKit>

Overview

Without callbacks, target/action is a hand-rolled pair: a target pointer, a function pointer, and a downcast in every handler. A callback combines them. &controller.onOK carries both the receiver and the code, the handler’s parameter is the typed sender, and there is no selector.

Two properties of that field make ownership safe. Both are guarantees of the language, not rules this class enforces: a callback never owns its receiver, and a stored callback auto-zeroes when that receiver dies.

1. It breaks the cycle. window → tree → control → action → controller → window would leak as a retain loop if the action were strong. AppKit solves this with a separate weak target field; here, the callback’s non-ownership breaks the cycle.
2. It makes a dead controller a silent no-op. if (action) tests both “no action set” and “the receiver has been deallocated” with the same syntax. A fired control whose controller died does nothing instead of calling into a stale object.

Neither needs a keyword, and you cannot opt out. Writing weak: on a callback is rejected, because there is nothing to opt into.

A block cannot be stored in the action field. A block owns its captures and a callback never owns its receiver, so the compiler refuses the conversion in both directions with a diagnostic that names the reason. Pass a callback.

How a click reaches your method depends on the backend, and your code does not see the difference. On GEM and the web the click routes through the tree hit-test into mouseDown. On Win32/macOS/iOS the native control notifies the driver, which fires the neutral widget directly by handle and node, with no synthetic click and no hit-test. Both paths end in fire.

Subclasses: UXButton (native everywhere), UXCheckbox and UXRadioButton (toggle-then-fire), UXLabel (a title with no action), UXTextField (which contains no editing code; the platform’s edit engine does the editing), and the value controls (slider, stepper, popup, segmented, progress).

Conforms to

• Inherits UXView.

Topics

setAction · setTitle · setAlignment · alignment · fire · mouseDown

setAction

void setAction(callback a void(UXControl* sender))

b.setAction(&controller.onOK), where the method has the UXAction shape: void onOK(UXControl* sender). Held weak; see the overview.

setTitle

void setTitle(u8* s)

The label. Borrowed, not copied; literals are the common case.

setAlignment / alignment

void setAlignment(i32 a)
i32  alignment(void)

How the control’s text sits in its frame: UX_ALIGN_LEFT, UX_ALIGN_RIGHT, UX_ALIGN_CENTER, UX_ALIGN_JUSTIFY.

Use it to line things up. A column of labels reading Name :, Size :, Kind : only has its colons aligned if the labels are right-aligned in equal frames. Left-aligned, the colons follow the words and the column looks broken.

The constants are GEM’s te_just values

UX_ALIGN_* uses the same numbers, so there is no translation anywhere. The value an application sets is the value the GEM backend puts in the TEDINFO, and the other backends map it to their own. With no conversion, there is no place for left and right to swap.

Setting it marks the control for redisplay; the next realize pushes it to the native control.

fire

void fire(void)

Calls action(self) if the action is set and its receiver is alive. One truth test covers both.

mouseDown

void mouseDown(UXEvent* e)

A control consumes its click (it does not pass it up the chain) and fires if enabled. Subclasses that carry state (checkbox, radio) flip it first, so the action reads the new state.

Example

One controller, three controls, no downcasts:

class Form : Object {
    UXCheckbox* agree;

    void onOK(UXControl* sender)     { if (agree.isChecked()) { self.submit(); } }
    void onCancel(UXControl* sender) { self.dismiss(); }
}

ok.setAction(&form.onOK);
cancel.setAction(&form.onCancel);
agree.setAction(&form.onAgree);