【学习ios之路:UI系列】绘图(drawRect)

实现代码如下:
①在自定义视图中定义3个属性

//记录线条的路径
@property (nonatomic, retain) NSMutableArray *paths;
//设置绘图过程中线条的颜色
@property (nonatomic, retain) UIColor *pathColor;
@property (nonatomic, assign) CGFloat pathWidth;
//撤销功能
- (void)undo;
//清除功能
- (void)clear;

②实现效果,需要在手指开始移动即移动过程中处理操作,即需要在下面两个方法中操作.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event; - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;

方法中实现:

//实现相应时间
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    //获取手指对象
    UITouch *touch =  [touches anyObject];
    //获取手指当前触摸点
    CGPoint startPoint = [touch locationInView:touch.view];
    //创建路径对象
    UIBezierPath *path = [UIBezierPath bezierPath];
    //设置路径的起始点
    [path moveToPoint:startPoint];
    //配置路径属性
    //线条宽度
    path.lineWidth = self.pathWidth;
   //线条结合处样式
    path.lineJoinStyle = kCGLineJoinRound; 
    //线条样式
    path.lineCapStyle = kCGLineCapRound;  
    //将路径添加到路径数组中
    [self.paths addObject:path];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    //获取手指对象
    UITouch *touch = [touches anyObject];
    //获取手指当前触摸的位置
    CGPoint currentPoint = [touch locationInView:touch.view];
    //获得当前路径
    UIBezierPath *path = [self.paths lastObject];
    //设置路径终点
    [path addLineToPoint:currentPoint];
    //该方法无需实现,只是通过它自动调用drawRect方法
    [self setNeedsDisplay];
}

③实现视图中自带方法(drawRect),代码如下:

- (void)drawRect:(CGRect)rect {
     [self.pathColor setStroke];
    //遍历所有路径
    for (UIBezierPath *path in self.paths) {
    path.usesEvenOddFillRule = YES;
        [self.pathColor setFill];
        //设置笔画的颜色
        [self.pathColor setStroke];
        //和所有的路径相连
       [path stroke];
    }
}

④属性实现懒加载 即实现消除 和撤销操作

- (NSMutableArray *)paths {
    if (!_paths) {
        self.paths = [NSMutableArray arrayWithCapacity:1];
    }
    return [[_paths retain] autorelease];
}
- (CGFloat)pathWidth {
    if (!_pathWidth) {
        _pathWidth = 1;
    }
    return _pathWidth;
}
//撤销功能
- (void)undo {
    //删除最后一条数据,路径
    [self.paths removeLastObject];
    [self setNeedsDisplay];
}
//清除功能
- (void)clear {
     //删除所有信息
    [self.paths removeAllObjects];
    [self setNeedsDisplay];
}

④实现将涂鸦图片保存到系统相册.
1)获取涂鸦图片(UIImage的分类方法),view即当前涂鸦的视图

  + (UIImage *)saveImageFromDrawView:(UIView *)view {
    //获取图形上下文(上下文在这两个Graphics之间有效或者在DracRect中有效)
    UIGraphicsBeginImageContext(view.frame.size);
    //2.将要保存的view的layer绘制到bitmap图形上下文中,完成拍照的功能
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    //从当前上下文获取图片
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    //结束操作
    UIGraphicsEndImageContext();
    return image;

2)将图片保存(写在button的触发事件中)

   //获取要保存的图片
    UIImage *image = [UIImage saveImageFromDrawView:self.nameView];
    //保存到相册
    UIImageWriteToSavedPhotosAlbum(image, self, nil, nil);

⑤滑动最下方的滑竿实现改变线条颜色,即线条的宽度.

//设置颜色
- (IBAction)colorAction:(UISlider *)sender { 
    //CGFloat value = sender.value;
    self.nameView.pathColor = [UIColor colorWithHue:sender.value saturation:sender.value brightness:sender.value alpha:sender.value];

}
//设置线条的宽度
- (IBAction)boldAction:(UISlider *)sender {
    self.nameView.pathWidth = sender.value;
}