How to select multiple elements in iron-selector by mouse drag

Question

How can I select multiple items inside an iron-selector by clicking, holding and dragging the mouse, or even by drawing a rectangle with the mouse, and selecting all the items under it?

I use Polymer 1.11.3 and iron-selector 2.1.0, and reading the documentation provided no obvious solution.

This is my actual element in which I want to enable the drag-selection:

My goal is to be able to click e.g. on Sunday 7, drag the mouse to 15, release the click, and have 7-15 selected.

Answer 1

To be able to select my mouse click and drag, do the following:

1. Set the css property user-select: none; to the element which holds your selectable items.

2. Add on-track="handleTrack" to the element which holds your selectable items.

3. Put this div somewhere in your element: <div id="selectionBox" style="position:absolute; top:0; left:0; height:0; width:0; border:2px solid #000; background-color:rgba(128, 128, 128, 0.3); z-index:999;"></div>

Then, add these functions to your element:

handleTrack: function(e) {
    switch(e.detail.state) {
        case "start":
            this.x1 = e.detail.x;
            this.y1 = e.detail.y;
            this.drawRectangle(this.x1, this.y1, this.x2, this.y2);
            break;
        case "track":
            this.x2 = e.detail.x;
            this.y2 = e.detail.y;
            this.drawRectangle(this.x1, this.y1, this.x2, this.y2);
            break;
        case "end":
            this.x2 = e.detail.x;
            this.y2 = e.detail.y;
            this.drawRectangle(0, 0, 0, 0);
            this.selectRectangle(e);
        break;
    }
},
drawRectangle: function(x1, y1, x2, y2) {
    this.$.selectionBox.style.left = x1 + 'px';
    this.$.selectionBox.style.top = y1 + 'px';
    this.$.selectionBox.style.width = (x2 - x1) + 'px';
    this.$.selectionBox.style.height = (y2 - y1) + 'px';
},
selectRectangle: function(e) {
    var tol = 20;
    var ironSelectors = Polymer.dom(e.currentTarget).querySelectorAll("iron-selector");
    ironSelectors.forEach(function(selector) {
        selector.items.forEach(function(i) {
            var el = i.getBoundingClientRect();
            if ((el.left+tol >= this.x1) && (el.top+tol >= this.y1) && (el.right-tol <= this.x2) && (el.bottom-tol <= this.y2)) {
                selector.select(i.value);
            }
        }.bind(this));
    }.bind(this));
}

This code also works if you have multiple iron-selector.

Answer 2

You can select multiple items in iron-selector with multi attribute:

 <iron-selector attr-for-selected="name" selected-items = "{{selected}}" multi>
    <div name="foo">Foo</div>
    <div name="bar">Bar</div>
    <div name="zot">Zot</div>
  </iron-selector>

Selected items will be an array at selected property.

DEMO