iOS13的presentViewController问题解决方

UIViewController的modalPresentationStyle属性，在iOS13之前默认值为UIModalPresentationFullScreen，iOS13中苹果将默认值改为了UIModalPresentationAutomatic。

而这个万恶的UIModalPresentationAutomatic，苹果文档只写了一句话：

For most view controllers, UIKit maps this style to the UIModalPresentationPageSheet style, but some system view controllers may map it to a different style.

所以几乎所有使用了custom presentViewController的页面全部会变成这个样纸：

为了保持iOS13与老版本的UI一致，最简单的办法就是全局将UIViewcontroller的modalPresentationStyle属性改回UIModalPresentationFullScreen。

这里我没太深入的思考，用runtime交换了下modalPresentationStyle的get方法，把我自己hack的get方法return出UIModalPresentationFullScreen就行了。

@implementation UIViewController (MDAdditions)

+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        SEL sel = @selector(modalPresentationStyle);
        SEL swizzSel = @selector(swiz_modalPresentationStyle);
        Method method = class_getInstanceMethod([self class], sel);
        Method swizzMethod = class_getInstanceMethod([self class], swizzSel);
        BOOL isAdd = class_addMethod(self, sel, method_getImplementation(swizzMethod), method_getTypeEncoding(swizzMethod));
        if (isAdd) {
            class_replaceMethod(self, swizzSel, method_getImplementation(method), method_getTypeEncoding(method));
        }else{
            method_exchangeImplementations(method, swizzMethod);
        }
    });
}

- (UIModalPresentationStyle)swiz_modalPresentationStyle {
    return UIModalPresentationFullScreen;
}

@end

当然重写presentViewController:方法之类的也可以，个人感觉区别不大。
有其他更好的改进意见欢迎提出。