接下來我們要講圖片的塗鴉，我們分開一點一點拓展，先給圖片上劃線
創建項目 起名testAddLine

接下來我們在默認生成的ViewController中添加一張圖片 待用
同時添加一個按鈕
復制代碼 代碼如下:
- (void)viewDidLoad { 
    [super viewDidLoad]; 
    // Do any additional setup after loading the view, typically from a nib. 
     
    UIImageView *imageV = [[UIImageView alloc]initWithFrame:CGRectMake(10, 120, screen_Width-20, screen_Height-150)]; 
    imageV.image = [UIImage imageNamed:@"640-960-1.jpg"]; 
    [self.view addSubview:imageV]; 
     
    UIButton *testBtn = [[UIButton alloc]initWithFrame:CGRectMake(screen_Width/2.0-60, 60, 120, 36)]; 
    [testBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal]; 
    [testBtn setTitle:@"添加直線" forState:UIControlStateNormal]; 
    [testBtn addTarget:self action:@selector(addLineAct:) forControlEvents:UIControlEventTouchUpInside]; 
    [self.view addSubview:testBtn]; 
} 
 
- (void)addLineAct:(id)sender{ 
    NSLog(@"測試按鈕"); 
} 

接下來我們創建一個UIView 用來添加直線 起名：DrawLine

創建幾個變量
復制代碼 代碼如下:
@property(nonatomic,strong) NSMutableArray * completeLines; //已經畫好的線條 存入數組 
@property(nonatomic,strong) NSMutableDictionary* LinesInProscess; //正在畫的線條 存入字典 
@property(nonatomic,strong) UIColor *lineColor;//線條顏色 
@property (nonatomic)float lineWidth;//線條的粗細 

初始化DrawLine
復制代碼 代碼如下:
//初始化 
- (id)initWithFrame:(CGRect)frame{ 
    if (self = [super initWithFrame:frame]) { 
        //初始化變量 
        _completeLines = [[NSMutableArray alloc]init]; 
        _LinesInProscess = [[NSMutableDictionary alloc]init]; 
        //設置透明背景 
        self.backgroundColor = [UIColor clearColor]; 
         
    } 
     
    return  self; 
} 

我們把線條單獨抽象出來 創建一個類 創建對象 起名 Line

線條 兩個屬性 起始點 結束點（這就是數學中的兩點確定一條直線）
給Line 類創建兩個屬性
復制代碼 代碼如下:
#import <Foundation/Foundation.h> 
#import <UIKit/UIKit.h> 
 
@interface Line : NSObject 
 
@property(nonatomic)CGPoint begin; //線條開始點 
 
@property(nonatomic)CGPoint end; //線條結束點 
 
@end 

接下來 我們重寫DrawLine 的  drawRect 方法  繪制線條
復制代碼 代碼如下:
// Only override drawRect: if you perform custom drawing. 
// An empty implementation adversely affects performance during animation. 
- (void)drawRect:(CGRect)rect { 
    // Drawing code 
     
    //獲取上下文 
    CGContextRef cgt=UIGraphicsGetCurrentContext(); 
    //設置線條寬度 
    CGContextSetLineWidth(cgt, self.lineWidth); 
    //設置線條兩端形狀為圓角 
    CGContextSetLineCap(cgt, kCGLineCapRound); 
     
    //設置顏色 
    [self.lineColor set]; 
    //繪制已經完成的線段 
    for (Line *line in _completeLines){ 
        CGContextMoveToPoint(cgt, [line begin].x, [line begin].y); 
        CGContextAddLineToPoint(cgt, [line end].x, [line end].y ); 
        CGContextStrokePath(cgt); 
    } 
     
     
    //繪制正在畫的線段 
    for (NSArray *v in _LinesInProscess) { 
        Line *line =[_LinesInProscess objectForKey:v]; 
        CGContextMoveToPoint(cgt, [line begin].x, [line begin].y); 
        CGContextAddLineToPoint(cgt, [line end].x, [line end].y ); 
        CGContextStrokePath(cgt); 
    } 
     
} 

實現幾個手指滑動方法 用來接受手指的位置畫線
復制代碼 代碼如下:
//清空畫板 
-(void)clearAll 
{ 
    [_completeLines removeLastObject]; 
    [_LinesInProscess removeAllObjects]; 
    [self setNeedsDisplay]; 
} 
 
 
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    //判斷是否連按 
    for (UITouch *t in touches) { 
        if ([t tapCount]>1) { 
            //第二次畫線時第一條線還未完成時結束畫線 
            [self clearAll]; 
            return; 
        } 
         
        //NSValue 作為鍵使用 
        NSValue *key=[NSValue valueWithNonretainedObject:t]; 
         
        // 根據觸摸位置創建Line對象 
        CGPoint loc=[t locationInView:self]; 
        Line *newLine=[[Line alloc]init ]; 
        newLine.begin=loc; 
        newLine.end=loc; 
        //將當前正在畫的線存入字典 
        [_LinesInProscess setObject:newLine forKey:key]; 
         
    } 
} 
 
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    //手指移動過程中按照當前手指的位置動態更新線條 
    for (UITouch * t in touches) { 
        NSValue *key=[NSValue valueWithNonretainedObject:t]; 
        // 找對象當前UITouch對象的Line對象 
        Line *line =[_LinesInProscess objectForKey:key]; 
         
        CGPoint loc=[t locationInView:self]; 
        line.end=loc; 
    } 
    [self setNeedsDisplay]; 
} 
 
-(void)endTouches:(NSSet *) touches 
{ 
    //畫線完成之後將當前線條加入_completeLines 數組中 同時刪除字典_LinesInProscess裡的線條 
    for (UITouch *t in touches) { 
        NSValue *key=[NSValue valueWithNonretainedObject:t]; 
        Line *line =[_LinesInProscess objectForKey:key]; 
        if (line) { 
            [_completeLines addObject:line]; 
            [_LinesInProscess removeObjectForKey:key]; 
        } 
    } 
    [self setNeedsDisplay]; 
} 
 
-(void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [self endTouches:touches]; 
} 
 
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    [self endTouches:touches]; 
} 

回到 ViewController中 給按鈕點擊事件中 添加DrawLine到ImageView上
復制代碼 代碼如下:
- (void)addLineAct:(id)sender{ 
    NSLog(@"測試按鈕"); 
     
    DrawLine *touchdrawView = [[DrawLine alloc]initWithFrame:imageV.frame]; 
 
    touchdrawView.lineColor = [UIColor yellowColor]; 
    touchdrawView.lineWidth = 5.0; 
    touchdrawView.tag = 902; 
    [self.view addSubview:touchdrawView]; 
     
     
} 

好了 運行程序試試
點擊 添加直線 按鈕之後 試試在圖片上畫線

帶剪頭的線條
在上面例子的基礎上稍微拓展一下，給線段末尾加上一個箭頭
給DrawLine 類中添的方法 drawRect 中添加一段代碼

復制代碼 代碼如下:
//添加剪頭 
double r = sqrt((line.end.x-line.begin.x)*(line.end.x-line.begin.x)+(line.begin.y-line.end.y)*(line.begin.y-line.end.y));//線條長度 
CGContextMoveToPoint(cgt,line.end.x,line.end.y); 
//P1 
CGContextAddLineToPoint(cgt,line.end.x-(10*(line.begin.y-line.end.y)/r),line.end.y-(10*(line.end.x-line.begin.x)/r)); 
//P3 
CGContextAddLineToPoint(cgt,line.end.x+(20*(line.end.x-line.begin.x)/r), line.end.y-(20*(line.begin.y-line.end.y)/r)); 
//P2 
CGContextAddLineToPoint(cgt,line.end.x+(10*(line.begin.y-line.end.y)/r),line.end.y+(10*(line.end.x-line.begin.x)/r)); 
 
CGContextAddLineToPoint(cgt, line.end.x,line.end.y); 
CGContextDrawPath(cgt,kCGPathFillStroke); 
CGContextStrokePath(cgt); 

以上方法的思路 就是在線段畫完之後 確定三個點 畫一個三角形作為箭頭形狀