MD Settings: Implementing modal popup/action menus.

chrome/browser/resources/settings/settings_action_menu.js

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+Polymer({
+  is: 'settings-action-menu',
+  extends: 'dialog',
+
+  /**
+   * List of all options in this action menu.
+   * @private {?NodeList<!Element>}
+   */
+  options_: null,
+
+  /**
+   * Index of the currently focused item.
+   * @private {number}
+   */
+  focusedIndex_: -1,
+
+  /**
+   * Reference to the bound window's resize listener, such that it can be
+   * removed on detach.
+   * @private {?Function}
+   */
+  onWindowResize_: null,
+
+  hostAttributes: {
+    tabindex: 0,
+  },
+
+  listeners: {
+    'keydown': 'onKeyDown_',
+    'tap': 'onTap_',
+  },
+
+  /** override */
+  attached: function() {
+    this.options_ = this.querySelectorAll('.dropdown-item');
+  },
+
+  /** override */
+  detached: function() {
+    this.removeResizeListener_();
+  },
+
+  /** @private */
+  removeResizeListener_: function() {
+    window.removeEventListener('resize', this.onWindowResize_);
+  },
+
+  /**
+   * @param {!Event} e
+   * @private
+   */
+  onTap_: function(e) {
+    if (e.target == this) {
+      this.close();
+      e.stopPropagation();
+    }
+  },
+
+  /**
+   * @param {!KeyboardEvent} e
+   * @private
+   */
+  onKeyDown_: function(e) {
+    if (e.key == 'Tab') {
+      this.close();
+      return;
+    }
+
+    if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')
+      return;
+
+    var nextOption = this.getNextOption_(e.key == 'ArrowDown' ? 1 : - 1);
+    if (nextOption)
+      nextOption.focus();
+
+    e.preventDefault();
+  },
+
+  /**
+   * @param {number} step -1 for getting previous option (up), 1 for getting
+   *     next option (down).
+   * @return {?Element} The next focusable option, taking into account
+   *     disabled/hidden attributes, or null if no focusable option exists.
+   * @private
+   */
+  getNextOption_: function(step) {
+    // Using a counter to ensure no infinite loop occurs if all elements are
+    // hidden/disabled.
+    var counter = 0;
+    var nextOption = null;
+    var numOptions = this.options_.length;
+
+    do {
+      this.focusedIndex_ =
+          (numOptions + this.focusedIndex_ + step) % numOptions;
+      nextOption = this.options_[this.focusedIndex_];
+      if (nextOption.disabled || nextOption.hidden)
+        nextOption = null;
+      counter++;
+    } while (!nextOption && counter < numOptions);
+
+    return nextOption;
+  },
+
+  /** @override */
+  close: function() {
+    // Removing 'resize' listener when dialog is closed.
+    this.removeResizeListener_();
+    HTMLDialogElement.prototype.close.call(this);
+    window.dispatchEvent(new CustomEvent('resize'));
+  },
+
+  /**
+   * Shows the menu anchored to the given element.
+   * @param {!Element} anchorElement
+   */
+  showAt: function(anchorElement) {
+    var rect = anchorElement.getBoundingClientRect();
+
+    // Ensure that the correct item is focused when the dialog is shown, by
+    // setting the 'autofocus' attribute.
+    this.focusedIndex_ = -1;
+    var nextOption = this.getNextOption_(1);
+
+    /** @suppress {checkTypes} */
+    (function(options) {
+      options.forEach(function(option) {
+        option.removeAttribute('autofocus');
+      });
+    })(this.options_);
+
+    if (nextOption)
+      nextOption.setAttribute('autofocus', true);
+
+    this.onWindowResize_ = this.onWindowResize_ || function() {
+      if (this.open)
+        this.close();
+    }.bind(this);
+    window.addEventListener('resize', this.onWindowResize_);
+
+    this.showModal();
+
+    if (new settings.DirectionDelegateImpl().isRtl()) {
+      var right = window.innerWidth - rect.left - this.offsetWidth;
+      this.style.right = right + 'px';
+    } else {
+      var left = rect.right - this.offsetWidth;
+      this.style.left = left + 'px';
+    }
+
+    // Attempt to show the menu starting from the top of the rectangle and
+    // extending downwards. If that does not fit within the window, fallback to
+    // starting from the bottom and extending upwards.
+    var top = rect.top + this.offsetHeight <= window.innerHeight ?
+        rect.top :
+        rect.bottom - this.offsetHeight - Math.max(
+            rect.bottom - window.innerHeight, 0);
+
+    this.style.top = top + 'px';
+  },
+});