Fixed warning: 'const' type qualifier on return type has no effect [-Wignored-qualifiers]
Fixed fields initialization order warnings [-Wreorder]
Fixed warning: comparison of integers of different signs [-Wsign-compare]
Fixed warning: auto property synthesis is synthesizing property not explicitly synthesized [-Wobjc-missing-property-synthesis]
Fixed warning: weak instance variable '_delegate' is accessed multiple times in this method but may be unpredictably set to nil; assign to a strong variable to keep the object alive [-Warc-repeated-use-of-weak]