Implement array-selector. Fixes #4154 #4230
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| * @param {*} item Item from `items` array to select | ||
| */ | ||
| select(item) { | ||
| let idx = this.items.indexOf(item); |
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this used to be O(1) in v1, but now it's O(n), I just hit this problem in iron-list...
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The removal of Collection ultimately drives this change since collection.getKey(item) was O(1). One option would be to introduce a selectIndex(idx) and deselectIndex(idx) API which would avoid the item->index lookup when the index is known apriori (e.g. selection following tap on a dom-repeat'ed item).
When you say ' I just hit this problem in iron-list...', what do you mean? You hit a real-world performance problem due to this particular implementation? Or a similar O(n) problem elsewhere?
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yea. I was mostly thinking about multi-selection using the shift key or any other pattern that triggers this path to select an item. In iron-list, I'll also need to call this.items.indexOf(item) to preserve item.selected in the model.
selectIndex(idx) 👌
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| _updateSelection(multi, itemsInfo) { | ||
| if (itemsInfo.path == 'items') { | ||
| let newItems = itemsInfo.base; |
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This observer might run even when newsItems is undefined causing a:
Uncaught TypeError: Cannot read property 'length' of undefined
from calculateSplices (array-splice.html:251)
| let splices = Polymer.ArraySplice.calculateSplices(newItems, lastItems); | ||
| this._applySplices(splices, lastItems); | ||
| } else { | ||
| this.clearSelection(); |
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clearSelection also initializes this.selected but not always. If lastItems is an array and I set multi=true after, then selected is undefined.
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I didn't totally grok how you could have a lastItems and selected be undefined, but I think I see a case where you could switch multi and not have selected reflect a clear selection (i.e., in single selection it should be null and in multi selection it should be []), so I updated so that clearSelection is always run when multi changes.
kevinpschaaf
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| this.linkPaths('selected.' + sidx, 'items.' + (idx + added - removed)); | ||
| let selected = new IntegerSet(); | ||
| let sidx = 0; | ||
| this._selectedSet.forEach(idx => { |
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Apparently, the new set is created here because adding to a set while inside forEach is not supported. If that's the confirmed, let's add a comment.
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Can't seem to confirm that root issue so this needs explanation.
| @@ -158,58 +187,48 @@ | |||
| } | |||
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| _applySplices(splices) { | |||
| let toRemove = []; | |||
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Need a comment here to explain a fundamental limitation of this approach: if an array is re-ordered the same element may be removed and re-added. In this case, it may not be detected as still being in the selection and therefore the selection will not be maintained in that case.
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Implements
<array-selector>for 2.x.Polymer.Elementclass syntaxPolymer.Collection; instead uses splice information to adjust linked indices between theitems&selectedarraysPolymer.ArraySplice(Levenshtein minimum edit distance algorithm); this makesarray-selectorcompatible with the proposed changes to object dirty checking in 2.0. However, this is a small break in API behavior (previously setting to a new array would clear selection; it no longer necessarily does).selectedarray/item (in 1.x you had to manually deselect first, which seemed onerous)Reference Issue
Fixes #4154