按钮流水布局

- (void)createBtn {
    
    CGFloat spacing = 10;
    
    CGFloat x = 0;
    CGFloat y = 10;
    CGFloat btnH = 40;
    for (int i = 0; i < _arr.count; i ++) {
        UIButton *btn = [UIButton buttonWithType:0];
        [btn setTitle:[_arr objectAtIndex:i] forState:UIControlStateNormal];
        [btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
        btn.backgroundColor = [UIColor lightGrayColor];
        btn.titleLabel.font = [UIFont systemFontOfSize:17];
        [btn addTarget:self action:@selector(clickBtn:) forControlEvents:UIControlEventTouchUpInside];
        [self.view addSubview:btn];
        
        CGSize titleSize = [[self.arr objectAtIndex:i] boundingRectWithSize:CGSizeMake(MAXFLOAT, btnH) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:btn.titleLabel.font} context:nil].size;
        
        CGFloat btnW = titleSize.width + 2 * spacing;
        if (x + btnW > SCREEN_WIDTH) {
            x = 0;
            y += btnH + spacing;
        }
        btn.frame = CGRectMake(x, y, btnW, btnH);
        x += btnW + spacing;
       
    }  
}