使用CaLayer创建的柱形图，使用方便，可定制
_chartView = [[ATBarChartVIew alloc] initWithFrame:CGRectMake(10, 100, 400, 400)];
_chartView.backgroundColor = [UIColor greenColor];
NSMutableArray *arr = [NSMutableArray arrayWithCapacity:1];
for (int i =0 ; i < 12; i++) {
BarChartItem *item = [[BarChartItem alloc] init];
item.xAisxTitle = [NSString stringWithFormat:@"第%d级",i];
item.dataArr = @[
@(arc4random() % 27 + 1),
@(arc4random() % 27 + 1),
];
[arr addObject:item];
}
_chartView.dataArr = arr;
[self.view addSubview:_chartView];