UITabBarController的代理方法

-(BOOL)tabBarController:(UITabBarController *)tabBarController shouldSelectViewController:(UIViewController *)viewController {
    if (viewController == self.viewControllers[3]) {
        picker = [[UIImagePickerController alloc]init];
        picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        [self presentViewController:picker animated:YES completion:nil];
        return NO;
    }
    return YES;
}