read_value_async
Description:
public async unowned Value? read_value_async (Type type, int io_priority, Cancellable? cancellable) throws Error
  
  Asynchronously request the this contents converted to the given type.
For local clipboard contents that are available in the given `GType`, the value will be copied directly. Otherwise, GDK will try to use [ func@content_deserialize_async] to convert the clipboard's data.
Parameters:
| this | 
           a `GdkClipboard`  | 
      
| type | 
           a `GType` to read  | 
      
| io_priority | 
           the I/O priority of the request  | 
      
| cancellable | 
           optional `GCancellable` object  | 
      
| callback | 
           callback to call when the request is satisfied  | 
      
| user_data | 
           the data to pass to callback function  |