A drop-in utility to customize input accessory view for `WKWebView`.

WKWebView+InputAccessory.h

#import <WebKit/WebKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface WKWebView (InputAccessory)

@property (nonatomic, nullable, setter=cy_setCustomInputAccessoryView:) UIView *cy_customInputAccessoryView;

@end

NS_ASSUME_NONNULL_END

WKWebView+InputAccessory.m

#import <objc/runtime.h>
#import <objc/message.h>

#import "WKWebView+InputAccessory.h"

#define PROTECT_SPI_SELECTOR(x) (x)

@implementation WKWebView (InputAccessory)

+ (void)load {
    Class WKContentViewClass = objc_getClass("WKContentView");
    SEL targetSEL = sel_registerName(PROTECT_SPI_SELECTOR("inputAccessoryViewForWebView"));
    Method targetMethod = class_getInstanceMethod(WKContentViewClass, targetSEL);
    IMP origIMP = method_getImplementation(targetMethod);
    
    SEL webViewSEL = sel_registerName(PROTECT_SPI_SELECTOR("webView"));
    method_setImplementation(targetMethod, imp_implementationWithBlock(^(id self) {
        WKWebView *webView = ((id (*)(id, SEL)) objc_msgSend)(self, webViewSEL);
        UIView *customInputAccessoryView = webView.cy_customInputAccessoryView;
        if (customInputAccessoryView) {
            return (id) customInputAccessoryView;
        }
        return ((id (*)(id, SEL)) origIMP)(self, targetSEL);
    }));
}

- (void)cy_setCustomInputAccessoryView:(UIView *)view {
    objc_setAssociatedObject(self, @selector(cy_customInputAccessoryView), view, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (UIView *)cy_customInputAccessoryView {
    return objc_getAssociatedObject(self, @selector(cy_customInputAccessoryView));
}

@end