on-drag

Arguments: split-bar

Returns the on-drag property of a split-bar widget. The value may be set at creation time by passing the :on-drag initarg to make-instance, or any time later by call (setf on-drag).

The value of this property should be the name of a function that will be called repeatedly as the user drags the split-bar interactively, or else nil to not call an on-drag function at all. The default value is nil. You may use setf to set the value of this property.

Typically it is more convenient to use the min-space-before and min-space-after properties to constrain split-bar movement, when that is adequate.

When the value is a function, it will be called once each time the system notices that the split-bar has moved to a new position during a drag. The function should accept two arguments, which will be the split-bar widget and an integer indicating the new position. The function should return an integer indicating the position to which the split-bar should be constrained. The return value should therefore be the value argument itself whenever there is no need to constrain the movement. An on-drag function may also perform arbitrary side effects before returning the constrained position integer.

The position integer argument works like the value property of the split-bar, indicating the distance in pixels from the top of the parent window's interior to the split-bar when it is horizontal, or the distance from the left side of the parent window's interior to a vertical split-bar.

The widgets in the widgets-to-move and widgets-to-resize properties will still be moved and resized as usual when there is an on-drag function, though they will be moved and resized according the new split-bar position as it was constrained by the on-drag function as well as by the min-space-before and min-space-after properties.

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This page is new in the 8.2 release.
Created 2016.6.21.