ios Navigation Bar 透明

-(void)viewWillAppear:(BOOL)animated{

[super viewWillAppear:animated];

[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];

[self.navigationController.navigationBar setShadowImage:[UIImage new]];

}

-(void)viewWillDisappear:(BOOL)animated{

[super viewWillDisappear:animated];

[self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];

[self.navigationController.navigationBar setShadowImage:nil];

}