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fix(core): make DefaultIterableDiffer keep the order of duplicates (#23941) 

Previously, in `_mismatch()`, the `DefaultIterableDiffer` first checks
`_linkedRecords` for `itemTrackBy`, then checks `_unlinkedRecords`.
This cause the `DefaultIterableDiffer` to move "later" items that match the
`itemTrackBy` from the old collection, rather than using the "earlier" one.

Now we check `_unlinkedRecords` first, so that the `DefaultIterableDiffer`
can give a more stable and reasonable result after diffing. For example,
rather than (`a1` and `a2` have same trackById)

```
a1 b c a2 => b a2 c a1
```

we get

```
a1 b c a2 => b a1 c a2
```

where a1 and a2 retain their original order despite both
having the same track by value.

Fixes #23815

PR Close #23941
This commit is contained in:
Sirui Chen 2018-05-17 00:36:17 +08:00 committed by Jessica Janiuk
parent cffb00ec11
commit a8269264bf
2 changed files with 70 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
packages/core/src/change_detection/differs/default_iterable_differ.ts
View File

@ -281,23 +281,24 @@ export class DefaultIterableDiffer<V> implements IterableDiffer<V>, IterableChan
this._remove(record);
}
// Attempt to see if we have seen the item before.
record = this._linkedRecords === null ? null : this._linkedRecords.get(itemTrackBy, index);
// See if we have evicted the item, which used to be at some anterior position of _itHead list.
record = this._unlinkedRecords === null ? null : this._unlinkedRecords.get(itemTrackBy, null);
if (record !== null) {
// We have seen this before, we need to move it forward in the collection.
// But first we need to check if identity changed, so we can update in view if necessary
// It is an item which we have evicted earlier: reinsert it back into the list.
// But first we need to check if identity changed, so we can update in view if necessary.
if (!Object.is(record.item, item)) this._addIdentityChange(record, item);
this._moveAfter(record, previousRecord, index);
this._reinsertAfter(record, previousRecord, index);
} else {
// Never seen it, check evicted list.
record = this._unlinkedRecords === null ? null : this._unlinkedRecords.get(itemTrackBy, null);
// Attempt to see if the item is at some posterior position of _itHead list.
record = this._linkedRecords === null ? null : this._linkedRecords.get(itemTrackBy, index);
if (record !== null) {
// It is an item which we have evicted earlier: reinsert it back into the list.
// But first we need to check if identity changed, so we can update in view if necessary
// We have the item in _itHead at/after `index` position. We need to move it forward in the
// collection.
// But first we need to check if identity changed, so we can update in view if necessary.
if (!Object.is(record.item, item)) this._addIdentityChange(record, item);
this._reinsertAfter(record, previousRecord, index);
this._moveAfter(record, previousRecord, index);
} else {
// It is a new item: add it.
record =

59
packages/core/test/change_detection/differs/default_iterable_differ_spec.ts
View File

@ -561,6 +561,65 @@ class ComplexItem {
}));
});
it('should keep the order of duplicates', () => {
const l1 = [
new ComplexItem('a', 'blue'),
new ComplexItem('b', 'yellow'),
new ComplexItem('c', 'orange'),
new ComplexItem('a', 'red'),
];
differ.check(l1);
const l2 = [
new ComplexItem('b', 'yellow'),
new ComplexItem('a', 'blue'),
new ComplexItem('c', 'orange'),
new ComplexItem('a', 'red'),
];
differ.check(l2);
expect(iterableDifferToString(differ)).toEqual(iterableChangesAsString({
collection: [
'{id: b, color: yellow}[1->0]', '{id: a, color: blue}[0->1]', '{id: c, color: orange}',
'{id: a, color: red}'
],
identityChanges: [
'{id: b, color: yellow}[1->0]', '{id: a, color: blue}[0->1]', '{id: c, color: orange}',
'{id: a, color: red}'
],
previous: [
'{id: a, color: blue}[0->1]', '{id: b, color: yellow}[1->0]', '{id: c, color: orange}',
'{id: a, color: red}'
],
moves: ['{id: b, color: yellow}[1->0]', '{id: a, color: blue}[0->1]'],
}));
});
it('should not have identity changed', () => {
const l1 = [
new ComplexItem('a', 'blue'),
new ComplexItem('b', 'yellow'),
new ComplexItem('c', 'orange'),
new ComplexItem('a', 'red'),
];
differ.check(l1);
const l2 = [l1[1], l1[0], l1[2], l1[3]];
differ.check(l2);
expect(iterableDifferToString(differ)).toEqual(iterableChangesAsString({
collection: [
'{id: b, color: yellow}[1->0]', '{id: a, color: blue}[0->1]', '{id: c, color: orange}',
'{id: a, color: red}'
],
previous: [
'{id: a, color: blue}[0->1]', '{id: b, color: yellow}[1->0]', '{id: c, color: orange}',
'{id: a, color: red}'
],
moves: ['{id: b, color: yellow}[1->0]', '{id: a, color: blue}[0->1]'],
}));
});
it('should track removals normally', () => {
const l = buildItemList(['a', 'b', 'c']);
differ.check(l);