代码部分
TouchView.h
代码如下：

#import <UIKit/UIKit.h> 
 
@interface TouchView : UIView 
{ 
    NSMutableArray *points; 
    NSArray *points_all; 
    CGContextRef context; 
    UIColor *paint_clr; 
} 
@property (strong,nonatomic) NSMutableArray *points; 
@property (strong,nonatomic) NSArray *points_all; 
@property (strong,nonatomic) UIColor *paint_clr; 
 
@end 

TouchView.m
代码如下：

#import "TouchView.h" 
 
@implementation TouchView 
@synthesize points, points_all, paint_clr; 
 
- (id)initWithFrame:(CGRect)frame 
{ 
    self = [super initWithFrame:frame]; 
    if (self) { 
        // Initialization code 
        paint_clr = [UIColor greenColor]; 
    } 
    return self; 
} 
 
// Only override drawRect: if you perform custom drawing. 
// An empty implementation adversely affects performance during animation. 
- (void)drawRect:(CGRect)rect 
{ 
    // Drawing code 
    if ((!self.points) || (self.points.count < 2)) { 
        return; 
    } 
       
    context = UIGraphicsGetCurrentContext(); 
    //设置画笔粗细  
    CGContextSetLineWidth(context, 5.0f); 
    //设置画笔颜色 
    //[[UIColor blueColor]set ]; 
    // [paint_clr set]; 
    //CGContextSetStrokeColorWithColor(context, [[UIColor blueColor]CGColor]); 
    CGContextSetStrokeColorWithColor(context, [paint_clr CGColor]); 
     
    //画以前的轨迹 
    for (int j = 0 ; j < [self.points_all count]; j++) { 
        NSMutableArray *points_tmp = [points_all objectAtIndex:j]; 
             
            for (int i = 0;i < [points_tmp count]-1;i++) 
            { 
                CGPoint point1 = [[points_tmp objectAtIndex:i] CGPointValue]; 
                CGPoint point2 = [[points_tmp objectAtIndex:(i+1)] CGPointValue]; 
                CGContextMoveToPoint(context, point1.x, point1.y); 
                CGContextAddLineToPoint(context, point2.x, point2.y); 
                CGContextStrokePath(context); 
            } 
        } 
     
    //画这次 
    for (int i=0; i < [self.points count]-1; i++) { 
        CGPoint point1 = [[self.points objectAtIndex:i] CGPointValue]; 
        CGPoint point2 = [[self.points objectAtIndex:(i+1)] CGPointValue]; 
        CGContextMoveToPoint(context, point1.x, point1.y); 
        CGContextAddLineToPoint(context, point2.x, point2.y); 
        CGContextStrokePath(context); 
    }     
} 
 
//不支持多点触摸 
- (BOOL) isMultipleTouchEnabled 
{ 
    return NO; 
} 
 
//创建一个array，并且记录初始ponit 
- (void) touchesBegan:(NSSet *) touches withEvent:(UIEvent *) event 
{ 
    self.points = [NSMutableArray array]; 
    CGPoint pt = [[touches anyObject] locationInView:self]; 
    [self.points addObject:[NSValue valueWithCGPoint:pt]]; 
} 
 
//移动过程中记录这些points 
//调用setNeedsDisplay，会触发drawRect方法的调用 
- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    CGPoint pt = [[touches anyObject] locationInView:self]; 
    [self.points addObject:[NSValue valueWithCGPoint:pt]]; 
    [self setNeedsDisplay]; 
} 
 
- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    NSMutableArray *points_tmp = [[NSMutableArray alloc] initWithArray:self.points]; 
    if (self.points_all == nil) { 
        self.points_all = [[NSArray alloc] initWithObjects:points_tmp, nil]; 
    }else { 
        self.points_all = [self.points_all arrayByAddingObject:points_tmp]; 
    } 
} 
@end 

ViewController.h
代码如下：

#import <UIKit/UIKit.h> 
 
@class TouchView; 
@interface ViewController : UIViewController 
{ 
    TouchView *tv; 
} 
@end 

ViewController.m
代码如下：

#import "ViewController.h" 
#import "TouchView.h" 
 
@interface ViewController () 
 
@end 
 
@implementation ViewController 
 
- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    // Do any additional setup after loading the view, typically from a nib. 
    self.view.userInteractionEnabled = YES; 
     
  // TouchView *tv = [[TouchView alloc]initWithFrame:CGRectMake(0.0f, 0.0f, 260.0f, 260.0f)]; 
    tv = [[TouchView alloc]initWithFrame:self.view.frame]; 
    tv.backgroundColor = [UIColor blackColor]; 
     
    [self.view addSubview:tv]; 
     
    UISegmentedControl *seg = [[UISegmentedControl alloc] initWithItems:[@"White Red Blue Green Yellow" componentsSeparatedByString:@" "]]; 
    seg.segmentedControlStyle = UISegmentedControlSegmentCenter; 
    seg.tintColor = [UIColor blackColor];  
    seg.center = CGPointMake(self.view.center.x, (self.view.bounds.size.height - seg.bounds.size.height));  
    [self.view addSubview:seg]; 
     
    [seg addTarget:self action:@selector(colorChange:) forControlEvents:UIControlEventValueChanged]; 
} 
 
- (void)viewDidUnload 
{ 
    [super viewDidUnload]; 
    // Release any retained subviews of the main view. 
} 
 
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation 
{ 
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown); 
} 
 
- (void) colorChange: (UISegmentedControl *) seg 
{ 
    switch ([seg selectedSegmentIndex]) 
    { 
        case 0:  
            tv.paint_clr = [UIColor whiteColor]; 
            break; 
        case 1: 
            tv.paint_clr = [UIColor redColor]; 
            break; 
        case 2: 
            tv.paint_clr = [UIColor blueColor]; 
            break; 
        case 3: 
            tv.paint_clr = [UIColor greenColor]; 
            break; 
        case 4: 
            tv.paint_clr = [UIColor yellowColor]; 
            break; 
        default: 
             
            break; 
    } 
} 
 
@end 

效果图