思路是将每一次按下屏幕的touch move时的点存到一个数组里，即一个数组相当于一个笔画；再将该代表笔画的数组保存到一个大数组中，每组每次touch的移动都历遍大数组和笔画数组，将点于点之间连接起来。
#import <UIKit/UIKit.h>
@interface BIDDrawView : UIView
{
NSMutableArray *allPoints;
} @end
#import "BIDDrawView.h" @implementation BIDDrawView - (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
allPoints=[[NSMutableArray alloc] init]; UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
btn.frame=CGRectMake(, , , );
[btn addTarget:self action:@selector(undo:) forControlEvents:UIControlEventTouchUpInside];
[self addSubview:btn];
}
return self;
} -(void)undo:(UIButton *)sender
{
if (allPoints.count>) { // 如果撤销有问题需要把该判断移除
[allPoints removeLastObject];
[self setNeedsDisplay];
}
} - (void)drawRect:(CGRect)rect
{
if (allPoints.count == ) {
return;
} CGContextRef ctx=UIGraphicsGetCurrentContext(); //获取画板，或者说获取画图上下文。
CGContextSetStrokeColorWithColor(ctx, [UIColor redColor].CGColor); //设置画笔颜色。
CGContextSetLineWidth(ctx, 1.5); //设置线条宽度。 for (NSMutableArray *points in allPoints) {
for (int i=;i<points.count-;i++) {
if (points.count==) {
break;
}
NSValue *sValue = [points objectAtIndex:i];
CGPoint sPoint=[sValue CGPointValue]; NSValue *eValue = [points objectAtIndex:i+];
CGPoint ePoint=[eValue CGPointValue]; CGContextMoveToPoint(ctx, sPoint.x, sPoint.y); //前往起点。
CGContextAddLineToPoint(ctx, ePoint.x, ePoint.y); //由起点加线到终点。 CGContextStrokePath(ctx);
}
}
} -(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
NSMutableArray *points = [NSMutableArray array];
[allPoints addObject:points];
} -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint p = [touch locationInView:self];
NSValue *v = [NSValue valueWithCGPoint:p]; //CGPoint 转为 对象
NSMutableArray *points = [allPoints lastObject];
[points addObject:v];
//驱动画笔（drawRect方法）
[self setNeedsDisplay];
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{}
@end
效果：