Cellforitematindexpath not called

The data source method that encountered Cellforitematindexpath the previous few days was not called. This is a data source method that CollectionView returns the cell (item).

It has not been called for the following reasons:

1. Delegate not set

2. The controller does not comply with the Uicollectiondatasource protocol

The return value in 3.numberOfItemsInSection is 0

4. This is also the case I encountered: is to initialize the CollectionView to pass a flowlayout, Then, if the value of Flowlayout.itemsize is not set (it cannot be 0), then the Cellforitematindexpath will not be called. Validation can be set to itemsize a fixed value such as (30,30), you can know that its data is wrong.

Cellforitematindexpath not called