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# forSelector(_:argumentIndex:ofReply:)

Returns the interface previously set for the specified selector and parameter.

```
func forSelector(_ sel: Selector, argumentIndex arg: Int, ofReply: Bool) -> NSXPCInterface?
```

## Parameters

`sel`

Specifies which method in the protocol you want information about.

`arg`

Specifies the position (starting at index 0) of the parameter for which you want to obtain the current interface. This may be either the position of a parameter in the method itself or the position in its reply block.

`ofReply`

Pass <doc://com.apple.documentation/documentation/Swift/true> if `arg` is an index into the parameters of the reply block, or <doc://com.apple.documentation/documentation/Swift/false> if it is an index into the parameters of the method itself.

## Discussion

See [`setInterface(_:for:argumentIndex:ofReply:)`](/documentation/Foundation/NSXPCInterface/setInterface(_:for:argumentIndex:ofReply:)) for more explanation.

---

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