众所周知，给图片添加圆角有CALayer的cornerRadius，

比如：

最直接的方法：

imgView.layer.cornerRadius1=110;
imgView.clipsToBounds = YES;

这事离屏渲染 （off - screen - rendering）， 是很消耗性能的；有很多公司面试的时候会问到，你怎么将图片设置圆角，如果你

只回答了这个方法，那么很遗憾，没有加分。

下面我介绍一种更好的方法：

#import "Bys.h"

@implementation Bys

- (UIImage*)imageWithCornerRadius:(CGFloat)radius{
   CGRect rect = (CGRect){0.f,0.f,self.size};
   // void UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale);
   //size——同UIGraphicsBeginImageContext,参数size为新创建的位图上下文的大小
   //    opaque—透明开关，如果图形完全不用透明，设置为YES以优化位图的存储。
   //    scale—–缩放因子
   UIGraphicsBeginImageContextWithOptions(self.size, NO, [UIScreen mainScreen].scale);
   //根据矩形画带圆角的曲线
   CGContextAddPath(UIGraphicsGetCurrentContext(), [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius].CGPath);
   [self drawInRect:rect];
   //图片缩放，是非线程安全的
   UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
   //关闭上下文
   UIGraphicsEndImageContext();
   return image;
}

给UIImage添加生成圆角图片的扩展API: 这是on-screen-rendering

iOS app启动的方式有哪些：

1. 自己启动（用户手动点击启动）
2. urlscheme启动（关于urlScheme的详解点击打开链接）
3. 本地通知启动 （自己写的本地通知启动，蓝牙模块的启动，地理围栏的启动）
4. 远程通知启动 （后台服务器的推送通知）

在appdelegate.m文件中

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

系统给的一些关于launchoption的字典里面的内容

UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsURLKey                   NS_AVAILABLE_IOS(3_0); // userInfo contains NSURL with launch URL
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsSourceApplicationKey     NS_AVAILABLE_IOS(3_0); // userInfo contains NSString with launch app bundle ID
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsRemoteNotificationKey    NS_AVAILABLE_IOS(3_0) __TVOS_PROHIBITED; // userInfo contains NSDictionary with payload
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsLocalNotificationKey     NS_AVAILABLE_IOS(4_0) __TVOS_PROHIBITED; // userInfo contains a UILocalNotification
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsAnnotationKey            NS_AVAILABLE_IOS(3_2); // userInfo contains object with annotation property list
UIKIT_EXTERN NSString *const UIApplicationProtectedDataWillBecomeUnavailable    NS_AVAILABLE_IOS(4_0);
UIKIT_EXTERN NSString *const UIApplicationProtectedDataDidBecomeAvailable       NS_AVAILABLE_IOS(4_0);
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsLocationKey              NS_AVAILABLE_IOS(4_0); // app was launched in response to a CoreLocation event.
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsNewsstandDownloadsKey    NS_AVAILABLE_IOS(5_0) __TVOS_PROHIBITED; // userInfo contains an NSArray of NKAssetDownload identifiers
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsBluetoothCentralsKey     NS_AVAILABLE_IOS(7_0); // userInfo contains an NSArray of CBCentralManager restore identifiers
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsBluetoothPeripheralsKey  NS_AVAILABLE_IOS(7_0); // userInfo contains an NSArray of CBPeripheralManager restore identifiers
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsShortcutItemKey          NS_AVAILABLE_IOS(9_0) __TVOS_PROHIBITED; // userInfo contains the UIApplicationShortcutItem used to launch the app.

// Key in options dict passed to application:[will | did]FinishLaunchingWithOptions and info for UIApplicationDidFinishLaunchingNotification
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsUserActivityDictionaryKey    NS_AVAILABLE_IOS(8_0); // Sub-Dictionary present in launch options when user activity is present
UIKIT_EXTERN NSString *const UIApplicationLaunchOptionsUserActivityTypeKey          NS_AVAILABLE_IOS(8_0); // Key in user activity dictionary for the activity type

UIKIT_EXTERN NSString *const UIApplicationOpenSettingsURLString NS_AVAILABLE_IOS(8_0);

// Keys for application:openURL:options:
UIKIT_EXTERN NSString *const UIApplicationOpenURLOptionsSourceApplicationKey NS_AVAILABLE_IOS(9_0);   // value is an NSString containing the bundle ID of the originating application
UIKIT_EXTERN NSString *const UIApplicationOpenURLOptionsAnnotationKey NS_AVAILABLE_IOS(9_0);   // value is a property-list typed object corresponding to what the originating application passed in UIDocumentInteractionController's annotation property
UIKIT_EXTERN NSString *const UIApplicationOpenURLOptionsOpenInPlaceKey NS_AVAILABLE_IOS(9_0);   // value is a bool NSNumber, set to YES if the file needs to be copied before use

如何判断如下:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    
    //用户自己点击启动
    if(!launchOptions)
    {
        NSLog(@"用户点击app启动");
    }
    else
    {
        NSURL *url = [launchOptions objectForKey:UIApplicationLaunchOptionsURLKey];
        //app 通过urlscheme启动
        if (url) {
            NSLog(@"app 通过urlscheme启动 url = %@",url);
        }
        UILocalNotification *localNotification = [launchOptions objectForKey:UIApplicationLaunchOptionsLocalNotificationKey];
        //通过本地通知启动
        if(localNotification)
        {
            NSLog(@"app 通过本地通知启动 localNotification = %@",localNotification);
        }
        NSDictionary *remoteCotificationDic = [launchOptions objectForKey:UIApplicationLaunchOptionsRemoteNotificationKey];
        //远程通知启动
        if(remoteCotificationDic)
        {
            NSLog(@"app 通过远程推送通知启动 remoteCotificationDic = %@",remoteCotificationDic);
        }
        //位置变动的通知
        if(launchOptions[@"UIApplicationLaunchOptionsLocationKey"])
        {
            //写你的重新定位的代码
        }
    }
    
    
    
    
    return YES;
}

SDWebImage没有提供下载图片后对图片进行调整后再缓存的扩展，唯一的办法是利用

- (UIImage *)imageManager:(SDWebImageManager *)imageManager transformDownloadedImage:(UIImage *)image withURL:(NSURL *)imageURL

这个代理方法去实现，在此处运用代理模式不大合理！因为SDWebImage是单例，这种自定义行为显然不属于全局范畴，明显应该用block传递。再者比如我想用它来加载图片，从网上下载后裁切成圆角再缓存就不行了，因为源码会根据下载下来的图片格式做相应缓存，就算你裁成圆角，并且UIImage本身已经是PNG格式了，但是因为你下载的时候原图是JPG格式的，那么还是会以JPG格式保存，透明部分也没了。

iOS中Layer的坐标系统:

效果:

代码实例如下:

- (void)viewDidLoad
{
    [super viewDidLoad];

    CAGradientLayer *colorLayer = [CAGradientLayer layer];
    colorLayer.frame    = (CGRect){CGPointZero, CGSizeMake(200, 200)};
    colorLayer.position = self.view.center;
    [self.view.layer addSublayer:colorLayer];

    // 颜色分配
    colorLayer.colors = @[(__bridge id)[UIColor redColor].CGColor,
      (__bridge id)[UIColor greenColor].CGColor,
      (__bridge id)[UIColor blueColor].CGColor];
    
    // 颜色分割线
    colorLayer.locations  = @[@(0.25), @(0.5), @(0.75)];
    
    // 起始点
    colorLayer.startPoint = CGPointMake(0, 0);
    
    // 结束点
    colorLayer.endPoint   = CGPointMake(1, 0);
}

颜色分配严格遵守Layer的坐标系统,locations,startPoint,endPoint都是以Layer坐标系统进行计算的.
而locations并不是表示颜色值所在位置,它表示的是颜色在Layer坐标系相对位置处要开始进行渐变颜色了.

CAGradientLayer 的这四个属性 colors locations startPoint endPoint 都是可以进行动画的哦.
附录:
稍微复杂点的动画效果

代码实例:

//
//  RootViewController.m
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import "RootViewController.h"
#import "YXGCD.h"

@interface RootViewController ()

@property (nonatomic, strong) GCDTimer  *timer;

@end

@implementation RootViewController

- (void)viewDidLoad
{
  [super viewDidLoad];

  CAGradientLayer *colorLayer = [CAGradientLayer layer];
  colorLayer.backgroundColor = [UIColor blueColor].CGColor;
  colorLayer.frame	= (CGRect){CGPointZero, CGSizeMake(200, 200)};
  colorLayer.position = self.view.center;
  [self.view.layer addSublayer:colorLayer];

  // 颜色分配
  colorLayer.colors = @[(__bridge id)[UIColor cyanColor].CGColor,
              (__bridge id)[UIColor orangeColor].CGColor,
              (__bridge id)[UIColor magentaColor].CGColor];
  
  // 起始点
  colorLayer.startPoint = CGPointMake(0, 0);
  
  // 结束点
  colorLayer.endPoint   = CGPointMake(1, 0);
  
  _timer = [[GCDTimer alloc] initInQueue:[GCDQueue mainQueue]];
  [_timer event:^{
    
    static CGFloat test = - 0.1f;
    
    if (test >= 1.1)
    {
      test = - 0.1f;
      [CATransaction setDisableActions:YES];
      colorLayer.locations  = @[@(test), @(test + 0.05), @(test + 0.1)];
    }
    else
    {
      [CATransaction setDisableActions:NO];
      colorLayer.locations  = @[@(test), @(test + 0.05), @(test + 0.1)];
    }
    
    test += 0.1f;
    
  } timeInterval:NSEC_PER_SEC];
  [_timer start];
}

@end

代码实例:

_timer = [[GCDTimer alloc] initInQueue:[GCDQueue mainQueue]];
  [_timer event:^{
    
    static CGFloat test = - 0.1f;
    
    if (test >= 1.1)
    {
      test = - 0.1f;
      [CATransaction setDisableActions:NO];
      colorLayer.locations  = @[@(test), @(test + 0.01), @(test + 0.011)];
    }
    else
    {
      [CATransaction setDisableActions:NO];
      colorLayer.locations  = @[@(test), @(test + 0.01), @(test + 0.011)];
    }
    
    test += 0.1f;
    
  } timeInterval:NSEC_PER_SEC];
  [_timer start];