Aligning UIToolBar items

In Xamarin iOS

Right aligned:

yourBar.SetItems(new [] { new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace), yourButton }, false);

Center Aligned:

var flexibleSpace = new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace);
yourBar.SetItems(new [] { flexibleSpace, yourButton, flexibleSpace}, false);

Add two UIBarButtonSystemItemFlexibleSpace items to your toolbar, to the left and right of your items

UIBarButtonItem *flexibleSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
[toolbar setItems:[NSArray arrayWithObjects:flexibleSpace, settingsButton,deleteButton,aboutButton, flexibleSpace, nil]];

Adding these as you would any other toolbar items will distribute space evenly between the two of them.

This can also be done right from a storyboard.

Just drag and drop items in the toolbar, and turn some of them into flexible or fixed space to get the desired effect. See the two examples below.