The UIVisualEffectView extension for customized blurRadius.

UIVisualEffectView+BlurRadius.h

//
//  UIVisualEffectView+BlurRadius.h
//  Created by Daniel Hsieh on 2018/8/22.
//

#import <UIKit/UIKit.h>

@interface UIVisualEffectView (BlurRadius)

@property (nonatomic) CGFloat blurRadius;

@end

UIVisualEffectView+BlurRadius.m

//
//  UIVisualEffectView+BlurRadius.m
//  Created by Daniel Hsieh on 2018/8/22.
//

#import "UIVisualEffectView+BlurRadius.h"

@implementation UIVisualEffectView (BlurRadius)

- (void)setBlurRadius:(CGFloat)blurRadius {
    objc_setAssociatedObject(self, @selector(blurRadius), @(blurRadius), OBJC_ASSOCIATION_ASSIGN);
    if (@available(iOS 9.0, *)) {
        UIBlurEffect *effect = [NSClassFromString(@"_UICustomBlurEffect") new];
        [effect setValue:@(blurRadius) forKeyPath:@"blurRadius"];
        self.effect = effect;
    } else {
        NSLog(@"Minimum OS requirement for iOS 9.0 or later.");
    }
}

- (CGFloat)blurRadius {
    return [objc_getAssociatedObject(self, _cmd) floatValue];
}

@end