Swift

button.setImage(UIImage(named:"test-image"), forState: .normal)

Objective C

[self.button setImage:[UIImage imageNamed:@"test-image"] forState:UIControlStateNormal];

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Multiple Control States

You can also set an image for multiple UIControlStates, for example to set the same image for the Selected and Highlighted state:

Swift

button.setImage(UIImage(named:"test-image"), forState:[.selected, .highlighted])

Objective C

[self.button setImage:[UIImage imageNamed:@"test-image"] forState:UIControlStateSelected|UIControlStateHighlighted];