详解iOS App中图片的线段涂鸦功能的添加方法

接下来我们要讲图片的涂鸦，我们分开一点一点拓展，先给图片上划线
创建项目 起名testAddLine

接下来我们在默认生成的ViewController中添加一张图片 待用
同时添加一个按钮


代码如下:

- (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:@"添加直线" forState:UIControlStateNormal]; 
    [testBtn addTarget:self action:@selector(addLineAct:) forControlEvents:UIControlEventTouchUpInside]; 
    [self.view addSubview:testBtn]; 
} 
 
- (void)addLineAct:(id)sender{ 
    NSLog(@"测试按钮"); 
}

接下来我们创建一个UIView 用来添加直线 起名：DrawLine

创建几个变量


代码如下:

@property(nonatomic,strong) NSMutableArray * completeLines; //已经画好的线条 存入数组 
@property(nonatomic,strong) NSMutableDictionary* LinesInProscess; //正在画的线条 存入字典 
@property(nonatomic,strong) UIColor *lineColor;//线条颜色 
@property (nonatomic)float lineWidth;//线条的粗细

初始化DrawLine

代码如下:

//初始化 
- (id)initWithFrame:(CGRect)frame{ 
    if (self = [super initWithFrame:frame]) { 
        //初始化变量 
        _completeLines = [[NSMutableArray alloc]init]; 
        _LinesInProscess = [[NSMutableDictionary alloc]init]; 
        //设置透明背景 
        self.backgroundColor = [UIColor clearColor]; 
         
    } 
     
    return  self; 
}

我们把线条单独抽象出来 创建一个类 创建对象 起名 Line

线条 两个属性 起始点 结束点（这就是数学中的两点确定一条直线）
给Line 类创建两个属性


代码如下:

#import <Foundation/Foundation.h> 
#import <UIKit/UIKit.h> 
 
@interface Line : NSObject 
 
@property(nonatomic)CGPoint begin; //线条开始点 
 
@property(nonatomic)CGPoint end; //线条结束点 
 
@end

接下来 我们重写DrawLine 的  drawRect 方法  绘制线条

代码如下:

// Only override drawRect: if you perform custom drawing. 
// An empty implementation adversely affects performance during animation. 
- (void)drawRect:(CGRect)rect { 
    // Drawing code 
     
    //获取上下文 
    CGContextRef cgt=UIGraphicsGetCurrentContext(); 
    //设置线条宽度 
    CGContextSetLineWidth(cgt, self.lineWidth); 
    //设置线条两端形状为圆角 
    CGContextSetLineCap(cgt, kCGLineCapRound); 
     
    //设置颜色 
    [self.lineColor set]; 
    //绘制已经完成的线段 
    for (Line *line in _completeLines){ 
        CGContextMoveToPoint(cgt, [line begin].x, [line begin].y); 
        CGContextAddLineToPoint(cgt, [line end].x, [line end].y ); 
        CGContextStrokePath(cgt); 
    } 
     
     
    //绘制正在画的线段 
    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); 
    } 
     
}

实现几个手指滑动方法 用来接受手指的位置画线

代码如下:

//清空画板 
-(void)clearAll 
{ 
    [_completeLines removeLastObject]; 
    [_LinesInProscess removeAllObjects]; 
    [self setNeedsDisplay]; 
} 
 
 
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    //判断是否连按 
    for (UITouch *t in touches) { 
        if ([t tapCount]>1) { 
            //第二次画线时第一条线还未完成时结束画线 
            [self clearAll]; 
            return; 
        } 
         
        //NSValue 作为键使用 
        NSValue *key=[NSValue valueWithNonretainedObject:t]; 
         
        // 根据触摸位置创建Line对象 
        CGPoint loc=[t locationInView:self]; 
        Line *newLine=[[Line alloc]init ]; 
        newLine.begin=loc; 
        newLine.end=loc; 
        //将当前正在画的线存入字典 
        [_LinesInProscess setObject:newLine forKey:key]; 
         
    } 
} 
 
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event 
{ 
    //手指移动过程中按照当前手指的位置动态更新线条 
    for (UITouch * t in touches) { 
        NSValue *key=[NSValue valueWithNonretainedObject:t]; 
        // 找对象当前UITouch对象的Line对象 
        Line *line =[_LinesInProscess objectForKey:key]; 
         
        CGPoint loc=[t locationInView:self]; 
        line.end=loc; 
    } 
    [self setNeedsDisplay]; 
} 
 
-(void)endTouches:(NSSet *) touches 
{ 
    //画线完成之后将当前线条加入_completeLines 数组中 同时删除字典_LinesInProscess里的线条 
    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 给按钮点击事件中 添加DrawLine到ImageView上

代码如下:

- (void)addLineAct:(id)sender{ 
    NSLog(@"测试按钮"); 
     
    DrawLine *touchdrawView = [[DrawLine alloc]initWithFrame:imageV.frame]; 
 
    touchdrawView.lineColor = [UIColor yellowColor]; 
    touchdrawView.lineWidth = 5.0; 
    touchdrawView.tag = 902; 
    [self.view addSubview:touchdrawView]; 
     
     
}

好了 运行程序试试
点击 添加直线 按钮之后 试试在图片上画线

带剪头的线条
在上面例子的基础上稍微拓展一下，给线段末尾加上一个箭头
给DrawLine 类中添的方法 drawRect 中添加一段代码

代码如下:

//添加剪头 
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));//线条长度 
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 就是在线段画完之后 确定三个点 画一个三角形作为箭头形状