// 什么時候調(diào)用:當(dāng)前控件即將顯示的時候才會調(diào)用這個方法繪制   // 作用:繪制內(nèi)容,以后只要想在一個view中繪制內(nèi)容,必須在drawRect里面繪制   - (void)drawRect:(CGRect)rect {    // 繪制曲線    // 1.獲取上下文    CGContextRef ctx = UIGraphicsGetCurrentContext();    // 2.拼接路徑    UIBezierPath *path = [UIBezierPath bezierPath];    // 設(shè)置起點(diǎn)    [path moveToPoint:CGPointMake(10, 125)];    // 描述曲線    [path addQuadCurveToPoint:CGPointMake(240, 125) controlPoint:CGPointMake(125, 240)];    [path addLineToPoint:CGPointMake(10, 125)];    // 3.添加路徑到上下文    CGContextAddPath(ctx, path.CGPath);    // 設(shè)置繪圖狀態(tài),一定要再渲染之前    // 設(shè)置顏色    [[UIColor redColor] setStroke];    // 設(shè)置線段的寬度    CGContextSetLineWidth(ctx, 15);    // 設(shè)置線段的頂角樣式    CGContextSetLineCap(ctx, kCGLineCaPRound);    // 設(shè)置連接樣式    CGContextSetLineJoin(ctx, kCGLineJoinRound);    // 4.渲染上下文    CGContextStrokePath(ctx);}

// 繪制兩條路徑的方法- (void)drawTwoLine{    // 1.獲取上下文    CGContextRef ctx = UIGraphicsGetCurrentContext();    // 2.拼接路徑,一個路徑中可以保存多條線段    UIBezierPath *path = [UIBezierPath bezierPath];    [path moveToPoint:CGPointMake(10, 10)];    [path addLineToPoint:CGPointMake(20, 20)];    // 3.把路徑添加到上下文    CGContextAddPath(ctx, path.CGPath);    // 一根線對應(yīng)一個路徑,只要繪制的線不連接,最好使用一根線對應(yīng)一個路徑的方法    path = [UIBezierPath bezierPath];    // 拼接另一根直線    // 默認(rèn)下一根線的起點(diǎn)就是上一根線的終點(diǎn)    // 設(shè)置第二根線的起點(diǎn)    //    [path moveToPoint:CGPointMake(20, 20)];    // 如果想要繪制不連接的線,重新設(shè)置起點(diǎn)    [path moveToPoint:CGPointMake(50, 50)];    [path addLineToPoint:CGPointMake(20, 200)];    // 3.把路徑添加到上下文    CGContextAddPath(ctx, path.CGPath);    // 4.渲染上下文    CGContextStrokePath(ctx);}

// 畫扇形    UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:center radius:100 startAngle:0 endAngle:M_PI_2 clockwise:YES];    [path addLineToPoint:center];    [path addLineToPoint:CGPointMake(self.bounds.size.height * 0.5 + 100, self.bounds.size.height * 0.5)];    // 關(guān)閉路徑:從路徑的終點(diǎn)連接到起點(diǎn)    [path closePath];    // 設(shè)置填充顏色    [[UIColor redColor] setFill];    // 設(shè)置描邊顏色    [[UIColor greenColor] setStroke];    //    [path stroke];    // 如果路徑不是封閉的,默認(rèn)會關(guān)閉路徑    [path fill];

#import "PieView.h"@implementation PieView// Only override drawRect: if you perform custom drawing.// An empty implementation adversely affects performance during animation.- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{   //重繪    [self setNeedsDisplay];}- (void)drawRect:(CGRect)rect {    // Drawing code    NSArray *data = @[@25,@25,@20,@30];    //圓心    CGPoint center = CGPointMake(self.bounds.size.width * 0.5, self.bounds.size.height * 0.5);    //角度    CGFloat radius = self.bounds.size.width * 0.5;    CGFloat startA = 0;    CGFloat endA = 0;    CGFloat angle = 0;    for (NSNumber *num in data) {        // 畫一個扇形        startA = endA;        angle = [num intValue] / 100.0 * M_PI * 2;        endA = startA + angle;       UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:startA endAngle:endA clockwise:YES];        [path addLineToPoint:center];        // set:同時設(shè)置描邊和填充顏色        [[self randomColor] set];        [path fill];    }}// 隨機(jī)顏色- (UIColor *)randomColor{    CGFloat r = arc4random_uniform(256) / 255.0;    CGFloat g = arc4random_uniform(256) / 255.0;    CGFloat b = arc4random_uniform(256) / 255.0;    return [UIColor colorWithRed:r green:g blue:b alpha:1];}@end效果圖：

- (void)drawRect:(CGRect)rect {    NSString *str = @"hello!";    // Attributes:屬性    // 給一個字符串添加屬性,可以叫富文本,顏色,字體大小,空心,陰影    // 利用這個屬性字典給文本添加屬性    NSMutableDictionary *strAttr = [NSMutableDictionary dictionary];    // key,value    // 如何找到設(shè)置文本的屬性key    // 描述了字體    strAttr[NSFontAttributeName] = [UIFont boldSystemFontOfSize:50];    // 設(shè)置描邊的顏色和寬度    strAttr[NSStrokeWidthAttributeName] = @1;    strAttr[NSStrokeColorAttributeName] = [UIColor redColor];    NSShadow *shadow = [[NSShadow alloc] init];    shadow.shadowColor = [UIColor yellowColor];    shadow.shadowOffset = CGSizeMake(10, 10);    shadow.shadowBlurRadius = 5;    // 陰影    strAttr[NSShadowAttributeName] = shadow;    // 文字顏色    strAttr[NSForegroundColorAttributeName] = [UIColor redColor];    [str drawAtPoint:CGPointZero withAttributes:strAttr];} 效果圖：

#import "SnowView.h"@implementation SnowView- (void)awakeFromNib{    // 設(shè)置定時器//    [NSTimer scheduledTimerWithTimeInterval:.1 target:self selector:@selector(setNeedsDisplay) userInfo:nil repeats:YES];    // 0.1 setNeedsDisplay 綁定一個標(biāo)識,等待下次刷新的時候才會調(diào)用drawRect方法    // 0.15 屏幕的刷新時間    // 定時器    // 每次屏幕刷新的時候就會調(diào)用,屏幕一秒刷新60次    CADisplayLink *link = [CADisplayLink displayLinkWithTarget:self selector:@selector(setNeedsDisplay)];    // 只要把定時器添加到主運(yùn)行循環(huán)就能自動執(zhí)行    [link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];    // setNeedsDisplay:底層并不會馬上調(diào)用drawRect,只會給當(dāng)前的控件綁定一個刷新的標(biāo)識,每次屏幕刷新的時候,就會把綁定了刷新(重繪)標(biāo)識的控件重新刷新(繪制)一次,就會調(diào)用drawRect去重繪    // 如果以后每隔一段時間需要重繪,一般不使用NSTimer,使用CADisplayLink,不會刷新的時候有延遲}// Only override drawRect: if you perform custom drawing.// An empty implementation adversely affects performance during animation.- (void)drawRect:(CGRect)rect {    // Drawing code    static CGFloat snowY = 0;    UIImage *image = [UIImage imageNamed:@"雪花"];    [image drawAtPoint:CGPointMake(0, snowY)];    snowY += 10;    if (snowY > rect.size.height) {        snowY = 0;    }}
效果圖：

#import "DrawView.h"@implementation DrawView// Only override drawRect: if you perform custom drawing.// An empty implementation adversely affects performance during animation.- (void)drawRect:(CGRect)rect {    // Drawing code    // 1.獲取上下文    CGContextRef ctx = UIGraphicsGetCurrentContext();    // 2.拼接路徑    UIBezierPath *path = [UIBezierPath bezierPath];    [path moveToPoint:CGPointMake(10, 125)];    [path addLineToPoint:CGPointMake(240, 125)];    // 3.把路徑添加到上下文    CGContextAddPath(ctx, path.CGPath);    // 保存當(dāng)前上下文的默認(rèn)狀態(tài)    CGContextSaveGState(ctx);    // 設(shè)置狀態(tài)    [[UIColor redColor] set];    CGContextSetLineWidth(ctx, 20);    // 渲染上下文    CGContextStrokePath(ctx);    // 創(chuàng)建第二根路徑    path = [UIBezierPath bezierPath];    [path moveToPoint:CGPointMake(125, 10)];    [path addLineToPoint:CGPointMake(125, 240)];    // 添加到上下文    CGContextAddPath(ctx, path.CGPath);    // 恢復(fù)下上下文狀態(tài)    // 取出之前的保存的狀態(tài)覆蓋掉當(dāng)前的狀態(tài)    CGContextRestoreGState(ctx);//    [[UIColor blackColor] set];//    CGContextSetLineWidth(ctx, 1);    // 4.渲染上下文到view的layer    // 在渲染之前,系統(tǒng)會查看下上下文的狀態(tài),根據(jù)狀態(tài)去渲染    CGContextStrokePath(ctx);}@end

#import "ViewController.h"@interface ViewController ()@property (nonatomic, weak) UIView *cover;@property (nonatomic, assign) CGPoint oriP;@property (weak, nonatomic) IBOutlet UIImageView *imageView;@property (weak, nonatomic) IBOutlet UIView *view1;@end@implementation ViewController- (UIView *)cover{    if (_cover == nil) {        UIView *view = [[UIView alloc] init];        view.backgroundColor = [UIColor blackColor];        view.alpha = 0.5;        _cover = view;        [self.view addSubview:view];    }    return _cover;}- (IBAction)pan:(UIPanGestureRecognizer *)sender {    // 獲取下當(dāng)前的觸摸    CGPoint curP = [sender locationInView:_imageView];    if (sender.state == UIGestureRecognizerStateBegan) {        // 記錄下一開始的位置        _oriP = curP;    }    // 計(jì)算下黑色蒙版的frame    CGFloat w = curP.x - _oriP.x;    CGFloat h = curP.y - _oriP.y;    self.cover.frame = CGRectMake(_oriP.x, _oriP.y, w, h);    if (sender.state == UIGestureRecognizerStateEnded) { // 手指抬起        // 裁剪圖片,生成一張新圖片        // 開啟位圖上下文        UIGraphicsBeginImageContextWithOptions(_imageView.bounds.size, NO, 0);        // 設(shè)置裁剪區(qū)域        UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.cover.frame];        [path addClip];        // 繪制圖片        [_imageView.layer renderInContext:UIGraphicsGetCurrentContext()];        // 生成圖片        UIImage *image = UIGraphicsGetImageFromCurrentImageContext();        // 關(guān)閉上下文        UIGraphicsEndImageContext();        _imageView.image = image;        [self.cover removeFromSuperview];    }}@end效果圖：截屏前

效果圖：截屏后

#import "ViewController.h"@interface ViewController ()@end@implementation ViewController// 只要用戶手指在圖片上拖動.就會調(diào)用- (IBAction)pan:(UIPanGestureRecognizer *)sender {    // 拖動的時候,擦除圖片的某一部分    // 獲取手指的觸摸點(diǎn)   CGPoint curP = [sender locationInView:sender.view];    // 計(jì)算擦除的frame    CGFloat wh = 30;    CGFloat x = curP.x - wh * 0.5;    CGFloat y = curP.y - wh * 0.5;    CGRect frame = CGRectMake(x, y, wh, wh);    // 開啟位圖上下文    UIGraphicsBeginImageContextWithOptions(sender.view.bounds.size, NO, 0);    // 獲取當(dāng)前的上下文    CGContextRef ctx = UIGraphicsGetCurrentContext();    // 把控件上的內(nèi)容渲染到上下文    [sender.view.layer renderInContext:ctx];    // 清除上下文中某一部分的內(nèi)容    CGContextClearRect(ctx, frame);    // 生成一張新的圖片    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();    // 關(guān)閉上下文    UIGraphicsEndImageContext();    // 重新顯示到UIImageView    UIImageView *imageV = (UIImageView *)sender.view;    imageV.image = image;}@end效果圖：擦除前：效果圖：擦除部分后：