两个button之间来回切换选中状态

@interface ViewController()
@property (nonatomic,strong)UIButton * selectButton;
@end

-(void)createUI{
    UIButton *button1 = [UIButton buttonWithType:UIButtonTypeCustom];
    [button1 setBackgroundImage:[UIImage imageNamed:@"选择"] forState:UIControlStateNormal];
    [button1 setBackgroundImage:[UIImage imageNamed:@"选择 (1)"] forState:UIControlStateSelected];

    [button1 addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];
    button1.backgroundColor = [UIColor redColor];
    button1.selected = YES;
//    把button1对象赋值给一个全局变量
    self.selectButton = button1;
    [self.view addSubview:button1];
    [button1 mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.mas_offset(50);
        make.top.mas_offset(50);
        make.size.mas_equalTo(CGSizeMake(50, 50));
    }];
    
    
    UIButton *button2 = [UIButton buttonWithType:UIButtonTypeCustom];
    [button2 setBackgroundImage:[UIImage imageNamed:@"选择"] forState:UIControlStateNormal];
    [button2 setBackgroundImage:[UIImage imageNamed:@"选择 (1)"] forState:UIControlStateSelected];
    [button2 addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];
    button2.backgroundColor = [UIColor redColor];

    [self.view addSubview:button2];
    [button2 mas_makeConstraints:^(MASConstraintMaker *make) {
        make.left.mas_offset(200);
        make.top.mas_offset(50);
        make.size.mas_equalTo(CGSizeMake(50, 50));
    }];
    
}

-(void)buttonClick:(UIButton *)button{
//    判断这个点击事件的button和selectButton是不是同一个对象，不是同一个，先把selectButton置为未选择状态（也就是把原来的button1的selected属性置为NO,）再把button2置为选择，把这个button2赋值给selectButton，依次循环
    if (button != self.selectButton) {
        self.selectButton.selected = NO;
        button.selected = YES;
        self.selectButton = button;
    }else{
        self.selectButton.selected = YES;
    }
}