Kotlin type mismatch !! and?

Question

I just recently started studying kotlin and when I changed Webrtc release to a newer one(1.0.22920) encountered following problem:

 Type mismatch: inferred type is PeerConnection? but PeerConnection was expected

Here is the part of code where the error occurs:

val rtcConfig = PeerConnection.RTCConfiguration(iceServers)
peerConnection = peerConnectionFactory.createPeerConnection(rtcConfig, getPeerConnectionMediaConstraints(), videoPeerConnectionListener)

Most likely this is due to the fact that in the Webrtc library createPeerConnection became @Nullable:

@Nullable
      public PeerConnection createPeerConnection(RTCConfiguration rtcConfig, MediaConstraints constraints, Observer observer) {
        long nativeObserver = PeerConnection.createNativePeerConnectionObserver(observer);
        if (nativeObserver == 0L) {
            return null;
        } else {
            long nativePeerConnection = nativeCreatePeerConnection(this.nativeFactory, rtcConfig, constraints, nativeObserver);
            return nativePeerConnection == 0L ? null : new PeerConnection(nativePeerConnection);
        }
    }

Attempt to put ? and !! in different places did not work.

I think that only my poor knowledge of kotlin separates me from solving the problem, can you help me?

Answer 1

Most probably because earlier you have declare the variable as not nullable:

var peerConnection: PeerConnection

And that means you cannot assign a @Nullablevalue to that variable. Change that to:

var peerConnection: PeerConnection?

Or you can force the value being returned to be non-null, (which I do not recommend) in which case:

peerConnection = peerConnectionFactory.createPeerConnection(rtcConfig, getPeerConnectionMediaConstraints(), videoPeerConnectionListener)!!

Notice the !! at the end.