Does setNeedsLayout call layoutSubviews?

A change in bounds of a view that is not yet in a view hierarchy will result in a call to layoutSubviews: when the view is eventually added to a view hierarchy. And just for completeness: these triggers do not directly call layoutSubviews, but rather call setNeedsLayout , which sets/raises a flag.

How do you use layoutIfNeeded?

LayoutIfNeeded() – Layout subviews immediately….An example of why you might need to call layoutIfNeeded within a single run loop:

  1. You resize a custom view containing a table view with a custom layout.
  2. A controller object asks the table view to scroll to some particular cell when handling a user event.

Should I override layoutSubviews?

layoutSubviews() The system calls this method whenever it needs to recalculate the frames of views, so you should override it when you want to set frames and specify positioning and sizing. However, you should never call this explicitly when your view hierarchy requires a layout refresh.

When removing a view from the view hierarchy what happens to the constraints?

They are forgotten and adding A to C again adds no constraints. These constraints should be added to SUBVIEW superview, thus CONTAINERVIEW. If you remove SUBVIEW by simply checking all the CONTAINERVIEW constraints you could see that two aren’t around anymore.

What is layoutIfNeeded?

layoutIfNeeded() Lays out the subviews immediately, if layout updates are pending.

When should I call updateConstraints?

When a property of your custom view changes in a way that would impact constraints, you can call this method to indicate that the constraints need to be updated at some point in the future. The system will then call updateConstraints() as part of its normal layout pass.

How do you invalidate constraints?

If we want to invalidate a view’s constraints, we should remove the old constraints, then call setNeedsUpdateConstraints. Our custom updateConstraints or updateViewConstraints methods can then provide the new constraints. Constraints should not be invalided in the updateConstraints method.

What does Documentation call a view that’s embedded in another view?

Views can host other views. Embedding one view inside another creates a containment relationship between the host view (known as the superview) and the embedded view (known as the subview).

What is viewDidLayoutSubviews?

Apple gave a very good explanation on this by saying that it is called to notify the view controller that its view has just laid out its subviews. In another word, viewDidLayoutSubviews is called every time the view is updated, rotated or changed or it’s bounds change .

When to call layoutsubviews instead of layoutifneeded?

If you want to update the layout of your views immediately, call the layoutIfNeeded method.”. This is right. The purpose of it is to consolidate all layout on a single call to layoutSubviews which is performed by the system at the appropriate time.

How is setneedslayout used in layoutifneeded?

setNeedsLayout actually calls layoutIfNeeded, so if your calling setNeedsDisplay there’s no reason to call layoutIfNeeded. In this way setNeedsLayout is a convenience method for calling layoutIfNeeded which does the heavy lifting.

Is the method layoutifneeded a synchronous call?

In contrast, the method layoutIfNeeded is a synchronous call that tells the system you want a layout and redraw of a view and its subviews, and you want it done immediately without waiting for the update cycle.

Is there a way to force a layout update?

If you look at the layoutSubviews documentation, it explicitly says this: You should not call this method directly. If you want to force a layout update, call the setNeedsLayout method instead to do so prior to the next drawing update. If you want to update the layout of your views immediately, call the layoutIfNeeded method.