These logic seems confused because the goal we want is to start nfc sharing when the current mode is MODE_PLAYER, but the code looks like to set mozNfc.onpeerready to null/handlePeerConnectivity when music app is in different mode.

Maybe we can write something like:

```javascript
// This can be in PlayerView.init() where we setup all the event listeners.
if (window.navigator.mozNfc)
  window.navigator.mozNfc.onpeerready = this.handleNFCPeerConnectivity;
...
// Check the current mode in handleNFCPeerConnectivity
handleNFCPeerConnectivity: function pv_handleNFCPeerConnectivity(event) {
  if (ModeManager.currentMode === MODE_PLAYER) {
    // It's player mode now we can share the file.
  }
}