Improve support for drag and drop

Documentation TBD

core/modules/widgets/droppable.js

@@ -0,0 +1,144 @@
+/*\
+title: $:/core/modules/widgets/droppable.js
+type: application/javascript
+module-type: widget
+
+Droppable widget
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var Widget = require("$:/core/modules/widgets/widget.js").widget;
+
+var DroppableWidget = function(parseTreeNode,options) {
+	this.initialise(parseTreeNode,options);
+};
+
+/*
+Inherit from the base widget class
+*/
+DroppableWidget.prototype = new Widget();
+
+/*
+Render this widget into the DOM
+*/
+DroppableWidget.prototype.render = function(parent,nextSibling) {
+	var self = this;
+	// Remember parent
+	this.parentDomNode = parent;
+	// Compute attributes and execute state
+	this.computeAttributes();
+	this.execute();
+	// Create element
+	var domNode = this.document.createElement("div");
+	domNode.className = "tc-droppable";
+	// Add event handlers
+	$tw.utils.addEventListeners(domNode,[
+		{name: "dragenter", handlerObject: this, handlerMethod: "handleDragEnterEvent"},
+		{name: "dragover", handlerObject: this, handlerMethod: "handleDragOverEvent"},
+		{name: "dragleave", handlerObject: this, handlerMethod: "handleDragLeaveEvent"},
+		{name: "drop", handlerObject: this, handlerMethod: "handleDropEvent"}
+	]);
+	// Insert element
+	parent.insertBefore(domNode,nextSibling);
+	this.renderChildren(domNode,null);
+	this.domNodes.push(domNode);
+	// Stack of outstanding enter/leave events
+	this.currentlyEntered = [];
+};
+
+DroppableWidget.prototype.enterDrag = function(event) {
+	if(this.currentlyEntered.indexOf(event.target) === -1) {
+		this.currentlyEntered.push(event.target);
+	}
+	// If we're entering for the first time we need to apply highlighting
+	$tw.utils.addClass(this.domNodes[0],"tc-dragover");
+};
+
+DroppableWidget.prototype.leaveDrag = function(event) {
+	var pos = this.currentlyEntered.indexOf(event.target);
+	if(pos !== -1) {
+		this.currentlyEntered.splice(pos,1);
+	}
+	// Remove highlighting if we're leaving externally. The hacky second condition is to resolve a problem with Firefox whereby there is an erroneous dragenter event if the node being dragged is within the dropzone
+	if(this.currentlyEntered.length === 0 || (this.currentlyEntered.length === 1 && this.currentlyEntered[0] === $tw.dragInProgress)) {
+		this.currentlyEntered = [];
+		$tw.utils.removeClass(this.domNodes[0],"tc-dragover");
+	}
+};
+
+DroppableWidget.prototype.handleDragEnterEvent  = function(event) {
+	this.enterDrag(event);
+	// Tell the browser that we're ready to handle the drop
+	event.preventDefault();
+	// Tell the browser not to ripple the drag up to any parent drop handlers
+	event.stopPropagation();
+};
+
+DroppableWidget.prototype.handleDragOverEvent  = function(event) {
+	// Check for being over a TEXTAREA or INPUT
+	if(["TEXTAREA","INPUT"].indexOf(event.target.tagName) !== -1) {
+		return false;
+	}
+	// Tell the browser that we're still interested in the drop
+	event.preventDefault();
+	event.dataTransfer.dropEffect = "copy"; // Explicitly show this is a copy
+};
+
+DroppableWidget.prototype.handleDragLeaveEvent  = function(event) {
+	this.leaveDrag(event);
+};
+
+DroppableWidget.prototype.handleDropEvent  = function(event) {
+	var self = this;
+	this.leaveDrag(event);
+	// Check for being over a TEXTAREA or INPUT
+	if(["TEXTAREA","INPUT"].indexOf(event.target.tagName) !== -1) {
+		return false;
+	}
+	var dataTransfer = event.dataTransfer;
+	// Remove highlighting
+	$tw.utils.removeClass(this.domNodes[0],"tc-dragover");
+	// Try to import the various data types we understand
+	$tw.utils.importDataTransfer(dataTransfer,null,function(fieldsArray) {
+		fieldsArray.forEach(function(fields) {
+			if(fields.title) {
+				self.performActions(fields.title,event);
+			}
+		});
+	});
+	// Tell the browser that we handled the drop
+	event.preventDefault();
+	// Stop the drop ripple up to any parent handlers
+	event.stopPropagation();
+};
+
+DroppableWidget.prototype.performActions = function(title,event) {
+	if(this.dropzoneActions) {
+		this.invokeActionString(this.dropzoneActions,this,event,{actionTiddler: title});
+	}
+};
+
+/*
+Compute the internal state of the widget
+*/
+DroppableWidget.prototype.execute = function() {
+	this.dropzoneActions = this.getAttribute("actions");
+	// Make child widgets
+	this.makeChildWidgets();
+};
+
+/*
+Selectively refreshes the widget if needed. Returns true if the widget or any of its children needed re-rendering
+*/
+DroppableWidget.prototype.refresh = function(changedTiddlers) {
+	return this.refreshChildren(changedTiddlers);
+};
+
+exports.droppable = DroppableWidget;
+
+})();