A block drag strategy is an object that determines how a block should handle drags. They implement the logic to make a block a draggable. Creating new block drag strategies lets you switch out how blocks should handle drags without having to deal with creating a custom selectable, or handling selection.
For example, you might want your block to duplicate on drag, rather than dragging normally. Block drag strategies allow you to do that.
Drag strategies have all the same methods as an IDraggable
,
besides the getRelativeToSurfaceXY
method.
Implementation
To create a drag strategy, you need to implement the
IDragStrategy
interface. This requires all the same methods
as the IDraggable
interface, except for the getRelativeToSurfaceXY
method,
which the block already implements.
You can follow the
instructions for implementing a draggable to
implement your drag strategy, but skip implementing getRelativeToSurfaceXY()
.
Usage
To use a custom drag strategy, you need to apply the drag strategy to each
instance of a block. You can do this in the init
method of your block, by
calling setDragStrategy
.
Blockly.Blocks['my_block'] = {
init: function() {
// Other initialization...
this.setDragStrategy(new MyDragStrategy());
// Other initialization...
}
}