自定义涂鸦DEMO

#import "DoodleView.h"

@implementation DoodleView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        //创建一个大数组用来保存画过的线
        self._lineArray = [NSMutableArray arrayWithCapacity:1];
        //创建撤销按钮
        UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
        button.frame = CGRectMake((frame.size.width - 100) / 2, 430, 100, 30);
        [button setTitle:@"撤销" forState:UIControlStateNormal];
        [button addTarget:self action:@selector(undo:) forControlEvents:UIControlEventTouchUpInside];
        [self addSubview:button];
        
    }
    return self;
}

-(void)undo:(UIButton *)button
{
    [__lineArray removeLastObject];
    //重绘界面
    [self setNeedsDisplay];
}

//要绘图必须重写这个方法
- (void)drawRect:(CGRect)rect
{
    //拿到VIEW的上下文,context用来得到绘图中的一些设置信息
    CGContextRef context = UIGraphicsGetCurrentContext();
   //设置画笔颜色
    CGContextSetStrokeColorWithColor(context,[UIColor yellowColor].CGColor);
    //设置画笔的粗细
    CGContextSetLineWidth(context, 2.0);
    //拿到每一笔中的小数组
    for (int i = 0; i < self._lineArray.count; i++) {
        NSMutableArray *arrayPoint = [__lineArray objectAtIndex:i];
        //在建一个循环，拿到小数组每一个点
        for (int j = 0; j < (int)arrayPoint.count - 1; j++) {
            //先拿到第一个点和第二个点
            NSValue *firstPointValue = [arrayPoint objectAtIndex:j];
            NSValue *secondPointValue = [arrayPoint objectAtIndex:j + 1];
            //将两个转化成CGPoint类型
            CGPoint firstPoint = [firstPointValue CGPointValue];
            CGPoint secondPoint = [secondPointValue CGPointValue];
            //把笔触移动到一个点
            CGContextMoveToPoint(context, firstPoint.x, firstPoint.y);
            //将第二个点的笔触与第一个连成一个路径
            CGContextAddLineToPoint(context, secondPoint.x, secondPoint.y);
        }
    }
    //绘制路径
    CGContextStrokePath(context);
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //创建一个小数组用来记录每一条线，将每一条线放入大数组保存
    NSMutableArray *arrayPoint = [NSMutableArray arrayWithCapacity:1];
    [__lineArray addObject:arrayPoint];
    
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    //取得手指移动的位置
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self];
    //将手指的点透过大数组来放入小数组中
    //取得小数组，每次加入可变数组的元素都在最后一位
    NSMutableArray *arrayPoint = [__lineArray lastObject];
//  [arrayPoint addObject:point];数组只能放对象类型，所以想把Point放入数组必须先转化成对  象类型
    NSValue *pointValue = [NSValue valueWithCGPoint:point];
    //将点加入数组中保存
    [arrayPoint addObject:pointValue];
    //重绘界面
    [self setNeedsDisplay];
//    NSLog(@"point = %@",NSStringFromCGPoint(point));
    
}

@end