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# needsDisplay(forKey:)

Returns a Boolean indicating whether changes to the specified key require the layer to be redisplayed.

```
class func needsDisplay(forKey key: String) -> Bool
```

## Parameters

`key`

A string that specifies an attribute of the layer.

## Return Value

<doc://com.apple.documentation/documentation/Swift/true> if the layer requires a redisplay.

## Discussion

Subclasses can override this method and return <doc://com.apple.documentation/documentation/Swift/true> if the layer should be redisplayed when the value of the specified attribute changes. Animations changing the value of the attribute also trigger redisplay.

The default implementation of this method returns <doc://com.apple.documentation/documentation/Swift/false>.

## See Also

[`defaultAction(forKey:)`](/documentation/QuartzCore/CALayer/defaultAction(forKey:))

Returns the default action for the current class.

[`defaultValue(forKey:)`](/documentation/QuartzCore/CALayer/defaultValue(forKey:))

Specifies the default value associated with the specified key.


---

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