CODEWITHSUNDEEP
polymerdom-repeat
Hubert
Hubert

Reputation: 495

Polymer: forcing dom-repeat to recalculate all the item's index

I have a dom-repeat which displays a large list of items (about 9000 of them).

I am trying to only display part of the items, so that I don't end up with a gigantic scrollbar. For that I am using a dom-if that only shows items that have an index larger than 10.

When the dom-repeat is sorted or filtered, each item's index is recalculated, so it works very well.

Then I am using iron-scroll-threshold to detect when the user has scrolled to the bottom of the page, and then I am increasing the number of items displayed.

The problem is, this is not recalculating the index - in other words I can't figure out how to "redraw" the dom-repeat.

Is there a way to force a dom-repeat to recalculate all the index? Calling this.$.list.render() doesn't seem to do it.

<template id="list" is="dom-repeat" id="table" items="{{items}}" sort="{{sortFuntion}}">
  <template is="dom-if" if="{{isShowItem(index)}}">
    [[item.name]]<br />
  </template>
</template>

<iron-scroll-threshold scroll-target="document" on-lower-threshold="showMoreData">
</iron-scroll-threshold>

<script>
Polymer({
  is: 'my-element',
  properties: {
   limit: {type: Number, value: 10}
  },
  isShowItem: function(index) {
    return (index < this.limit);
    // we only show the items that have an index smaller than "limit" 
    // (the index is recalculated for each sort or filter, so it works well).
  },
  showMoreData: function() {
    // this is called by iron-scroll-threshold when we scroll down the page
    this.set("limit", this.limit + 10);
    // this is what doesn't seem to do anything:
    // (ideally we want it to recalculate each item's index)
    this.$.list.render(); 
  }
});
</script>

Upvotes: 0

Views: 263

Answers (1)

Rickard Elim&#228;&#228;
Rickard Elim&#228;&#228;

Reputation: 7591

I never use filter or sort in a dom-repeat but instead insert a method in items. Then I can control all sorts of stuff.

<template id="list" is="dom-repeat" id="table" items="[[_filterItems(items, scrollHeight)]]" sort="[[sortFuntion]]">
  ##code
</template>

---
<script>
  Polymer({

   ## properties and other methods

   _filterItems(items, scrollHeight) {  // ex. scrollHeight = 100
      var interpolationLevel = 5; // px
      var minAllowedItems = 10;
      var showThisManyItems = scrollHeight / interpolationLevel; // 100 / 5
      showThisManyItems (showThisManyItems < minAllowedItems) ? minAllowedItems : showThisManyItems; // 100 / 5 = 20, but min value == 10

      return items.filter(item, index) {
         return index < showThisManyItems;   // show this item if index < 20
      }
    },
  }
</script>

Upvotes: 1

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