# getCallbackHandle method

CallbackHandle getCallbackHandle (Function callback)

Get a handle to a named top-level or static callback function which can be easily passed between isolates.

The `callback` argument must not be null.

Returns a CallbackHandle that can be provided to PluginUtilities.getCallbackFromHandle to retrieve a tear-off of the original callback. If `callback` is not a top-level or static function, null is returned.

## Implementation

    static CallbackHandle getCallbackHandle(Function callback) {
      assert(callback != null, "'callback' must not be null.");
      return _forwardCache.putIfAbsent(callback, () {
        final int handle = _getCallbackHandle(callback);
        return handle != null ? new CallbackHandle.fromRawHandle(handle) : null;
      });
    }