fix(drag-drop): error when dragging items inside transplanted views with OnPush change detection #18356
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…ith OnPush change detection This is a bit of an edge case, but nevertheless it's something that can happen. The way the dragging sequence works is that the drop list keeps track of its items via `ContentChildren` and it registers itself with them once they're picked up by the `QueryList`. If an item doesn't have a container when the drag sequence is started, it is considered a "standalone" drag. This becomes a problem with transplanted views (e.g. ones created by `cdk-table`) that use OnPush where we could end up in a situation where the items aren't picked up during the first pass, but when the user starts dragging, we trigger change detection and the `QueryList` is updated, but at that point it's too late, because we've already started the dragging sequence with a different set of information. These changes work around the issue by assigning the container manually again through the drag directive. A couple of notes: * This is a second iteration of the fix. I went with this approach, because it doesn't require hacky timeouts and triggering change detection again. See the origin approach here: angular@22afc37 * It's difficult to capture this in a test, because we'd have to duplicate half of the logic from `CdkTable` and we might still not be able to get the same change detection timing due to `TestBed`. Fixes angular#18341.
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Confirmed in cl/293831687 that this fixes #15948. |
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This is a bit of an edge case, but nevertheless it's something that can happen. The way the dragging sequence works is that the drop list keeps track of its items via `ContentChildren` and it registers itself with them once they're picked up by the `QueryList`. If an item doesn't have a container when the drag sequence is started, it is considered a "standalone" drag. This becomes a problem with transplanted views (e.g. ones created by `cdk-table`) that use OnPush where we could end up in a situation where the items aren't picked up during the first pass, but when the user starts dragging, we trigger change detection and the `QueryList` is updated, but at that point it's too late, because we've already started the dragging sequence with a different set of information. These changes work around the issue by assigning the container manually again through the drag directive. A couple of notes: * This is a second iteration of the fix. I went with this approach, because it doesn't require hacky timeouts and triggering change detection again. See the origin approach here: 22afc37 * It's difficult to capture this in a test, because we'd have to duplicate half of the logic from `CdkTable` and we might still not be able to get the same change detection timing due to `TestBed`. Fixes #18341.
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This is a bit of an edge case, but nevertheless it's something that can happen. The way the dragging sequence works is that the drop list keeps track of its items via
ContentChildrenand it registers itself with them once they're picked up by theQueryList. If an item doesn't have a container when the drag sequence is started, it is considered a "standalone" drag.This becomes a problem with transplanted views (e.g. ones created by
cdk-table) that use OnPush where we could end up in a situation where the items aren't picked up during the first pass, but when the user starts dragging, we trigger change detection and theQueryListis updated, but at that point it's too late, because we've already started the dragging sequence with a different set of information.These changes work around the issue by assigning the container manually again through the drag directive.
A couple of notes:
CdkTableand we might still not be able to get the same change detection timing due toTestBed.Fixes #18341.