cocoa touch——UIImage——create，init

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create

bundle(cache)

+ (nullable UIImage *)imageNamed:(NSString *)name;      // load from main bundle#if __has_include(<UIKit/UITraitCollection.h>)+ (nullable UIImage *)imageNamed:(NSString *)name inBundle:(nullable NSBundle *)bundle compatibleWithTraitCollection:(nullable UITraitCollection *)traitCollection NS_AVAILABLE_IOS(8_0);#endif

注意：

前者是后者的特定版本，相当于后者的bundle为nil(main bundle，app)，traitCollection为nil(main screen)
name可能是asset catalogs中的image asset名，也可能是图像文件名
name是图像文件名时，如果是PNG，可以省略文件扩展名.png，如果是其他格式图像文件，不能省略
bundle中的图像system cache，提高了图像访问性能，但增加了app 内存消耗

file

+ (nullable UIImage *)imageWithContentsOfFile:(NSString *)path;

NSData

+ (nullable UIImage *)imageWithData:(NSData *)data;+ (nullable UIImage *)imageWithData:(NSData *)data scale:(CGFloat)scale NS_AVAILABLE_IOS(6_0);

Quartz(CGImage)

+ (UIImage *)imageWithCGImage:(CGImageRef)cgImage;+ (UIImage *)imageWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(4_0);

Core Image(CIImage)

#if __has_include(<CoreImage/CoreImage.h>)+ (UIImage *)imageWithCIImage:(CIImage *)ciImage NS_AVAILABLE_IOS(5_0);+ (UIImage *)imageWithCIImage:(CIImage *)ciImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(6_0);#endif

init

file

- (nullable instancetype)initWithContentsOfFile:(NSString *)path;

注意：

path必须包含文件扩展名用来识别图像类型(格式)
此方法把file的image data加载入内存，并且标记可清除，如果image data在内存中被清除，可以重读path指定的文件重新加载

NSData

- (nullable instancetype)initWithData:(NSData *)data;- (nullable instancetype)initWithData:(NSData *)data scale:(CGFloat)scale NS_AVAILABLE_IOS(6_0);

注意：

data数据格式必须符合系统支持的图像格式之一

Quartz(CGImage)

- (instancetype)initWithCGImage:(CGImageRef)cgImage;- (instancetype)initWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(4_0);

Core Image(CIImage)

#if __has_include(<CoreImage/CoreImage.h>)- (instancetype)initWithCIImage:(CIImage *)ciImage NS_AVAILABLE_IOS(5_0);- (instancetype)initWithCIImage:(CIImage *)ciImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(6_0);#endif

image

bundle(cache)

#if __has_include(<UIKit/UITraitCollection.h>)@property (nonatomic, readonly, copy) UITraitCollection *traitCollection NS_AVAILABLE_IOS(8_0); // describes the image in terms of its traits@property (nullable, nonatomic, readonly) UIImageAsset *imageAsset NS_AVAILABLE_IOS(8_0); // The asset is not encoded along with the image. Returns nil if the image is not CGImage based.#endif

Quartz(CGImage)

@property(nullable, nonatomic,readonly) CGImageRef CGImage; // returns underlying CGImageRef or nil if CIImage based- (nullable CGImageRef)CGImage NS_RETURNS_INNER_POINTER CF_RETURNS_NOT_RETAINED;

Core Image(CIImage)

#if __has_include(<CoreImage/CoreImage.h>)@property(nullable,nonatomic,readonly) CIImage *CIImage NS_AVAILABLE_IOS(5_0); // returns underlying CIImage or nil if CGImageRef based#endif

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