[iOS] Fix MeasureFirstItem for CollectionView #7622
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| ConstrainedDimension = constraint.Height; | ||
| Layout(constraint); |
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@hartez Previously, there was a Layout() call inside ConstrainTo(), but PreferredLayoutAttributesFittingAttributes does layout too. Any reason for that? Removing the call here made cell sizing better.
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TBH, I don't know why there was a Layout call there. Seems to work fine without it.
| // Measure this cell (including the Forms element) | ||
| var size = Measure(); | ||
| // Measure this cell (including the Forms element) if there is no constrained size | ||
| var size = ConstrainedSize == default(CGSize) ? Measure() : ConstrainedSize; |
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The reason MeasureFirstItem was broken is we were measuring here and assigning a new size to the cell. Since MeasureFirstItem constrains us to the first item, I added ConstrainedSize which is passed down from PrepareCellForLayout() in ItemsViewLayout as ItemSize.
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| // Reset constrained size in case ItemSizingStrategy changes | ||
| // and we want to measure each item | ||
| ConstrainedSize = default(CGSize); |
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You could test this functionality in CollectionView Galleries -> Item Size Galleries -> ItemSizing Strategy.
- Changing
ItemSizingStrategyto measure all should measure each cell inPreferredLayoutAttributesFittingAttributes. - Changing
ItemSizingStrategyto measure all and then back to measure first should not break measure first.
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@rmarinho I'll drop the private keyword from here too once the tests are done. |
| ConstrainedDimension = constraint.Height; | ||
| Layout(constraint); |
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TBH, I don't know why there was a Layout call there. Seems to work fine without it.
* fix MeasureFirstItem * added test * changed file name * fix path * added text * remove 5455 * drop private fixes xamarin#7621
* fix MeasureFirstItem * added test * changed file name * fix path * added text * remove 5455 * drop private fixes xamarin#7621
Description of Change
While looking at #5455, I noticed
MeasureFirstItemdoes not work either. I provided a button to switch betweenMeasureFirstItemandMeasureAllItems. You could use this test as well as the gallery test in #5455 when figuring out a fix forMeasureAllItems.MeasureAllItems:
To me,
MeasureAllItemsseems to be working in the test provided here. I assumed that each column would be as wide as the largest item in that column, and the other item would be centered. This is the case in this test. However, the first item is left aligned when the page is initially shown. If you scroll right and left, you'll see that the first item will be centered eventually. Something seems odd about the 4th (yellow) item. I was expecting it to be a bit wider since there is a lot of empty space to leverage. My head hurts too much right now to think about imageAspectFitvs CollectionView item sizing, so I wanted to document it here for now. :)Issues Resolved
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