使用block函数的基本形式

@property (nonatomic, copy) void(^fontValueChangedBlock)(void);

_fontValueChangedBlock = ^(){
    [self.fontSmallButton addTarget:self action:@selector(btnFontSmallClicked) forControlEvents:UIControlEventTouchUpInside];
        };
self.fontValueChangedBlock();

- (void)btnFontSmallClicked {
    NSLog(@"正文字体大小为 - 14号");
}