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Knockout.js Drag and Drop binding
Drag and drop is done using drop and drag zones. Each zone has a name. In the most simple case all you need is a drag zone and one or more drop zones. For example:
<div data-bind="dropzone: 'myzone'">...</div>
<div data-bind="dragzone: 'myzone'">...</div>
Drop zones
Of course you will probably want to receive an event when a drop has occured so you use the advanced drop zone options:
<div data-bind="dropzone: { name: 'myzone', drop: onDrop }">...</div>
The name property gives the dropzone a name. The drop callback will be called when a drop is complete. Besides drop you can also set up callbacks for dragenter and dragleave which will be called when a dragged object enters the drag zone and leaves the drag zone. You can use these callbacks to insert and remove marker elements, for example to indicate where a dragged object will be inserted if it is dropped.
The dragenter and dragleave callbacks will be passed the Knockout.js data binding for the dragged element and the drag and drop zone name. The drop callback will be passed the data binding for both the dragged element and the element it is dropped on, as well as the drag and drop zone name.
Drag zones
The drag zone binding also has a set of advanced options that lets you receive callbacks dragstart when the drag starts and dragend when the drag ends. The dragend callback is not called when the dragged elements is succesfulyy dropped. In this case the drop callback on the drop zone is called.
<div data-bind="dragzone: { name: 'myzone', dragstart: onStart, dragend: onEnd }">...</div>
You can use these two callbacks to add special styling to the element that is being dragged.
Data
The drag and drop binding will attempt to use the data binding on the element it is present on, such as a text or a value binding, but if there is no suitable binding you can also use the data property on both the drag and drop zone to bind to an object or observable:
<div data-bind="dragzone: { name: 'myzone', data: myObservable }">...</div>
<div data-bind="dropzone: { name: 'myzone', data: myObject, drop: onDrop }">...</div>
So when the myzone drag zone is dropped on the myzone dropzone, in the above example, the onDrop function will be called with myObservable and myObject.