UIImage 类说明

+ (UIImage *)imageNamed:(NSString *)name
               inBundle:(NSBundle *)bundle
compatibleWithTraitCollection:(UITraitCollection *)traitCollection

　　name：图片的名字。bundle：设置为nil则默认为main bundle。traitCollection：设置为nil则为main screen中描述的traits。

　　该方法在系统的缓存中查找具有指定名字和特征集的图像并返回。如果在缓存中没有找到，该方法将定位到disk和asset catalog查找图像。如果没有合适的图像，将返回nil。

+ (UIImage *)imageNamed:(NSString *)name

　　如果屏幕的scale为2.0，该方法首先搜索带@2x后缀的文件名。如，name = @“button"，会先搜索button@2x的文件。

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创建新的图像对象

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

　　path参数可为绝对路径或者相对路径。该方法不会缓存图像对象。

+ (UIImage *)imageWithData:(NSData *)data

+ (UIImage *)imageWithData:(NSData *)data
                     scale:(CGFloat)scale

　　如果scale = 1.0，将使得图像的大小跟基于像素的图像大小相匹配。如果scale = 2.0，图像的大小将会改变。

+ (UIImage *)imageWithCGImage:(CGImageRef)cgImage　　

+ (UIImage *)imageWithCGImage:(CGImageRef)imageRef
                        scale:(CGFloat)scale
                  orientation:(UIImageOrientation)orientation

　　orientation指定图像的方向。

+ (UIImage *)imageWithCIImage:(CIImage *)ciImage

+ (UIImage *)imageWithCIImage:(CIImage *)ciImage
                        scale:(CGFloat)scale
                  orientation:(UIImageOrientation)orientation

- (UIImage *)imageWithAlignmentRectInsets:(UIEdgeInsets)alignmentInsets

+ (UIImage *)animatedImageNamed:(NSString *)name
                       duration:(NSTimeInterval)duration

　　name：绝对路径或相对路径，无后缀。

+ (UIImage *)animatedImageWithImages:(NSArray<UIImage *> *)images
                            duration:(NSTimeInterval)duration

　　images：UIImage对象组成的数组，全部的图像应当具有相同的size和scale。

+ (UIImage *)animatedResizableImageNamed:(NSString *)name
                               capInsets:(UIEdgeInsets)capInsets
                                duration:(NSTimeInterval)duration

　　如果name = @"image"，这个方法会尝试去加载文件名为image0，image1, ... , image1024的图像。全部图像应具有相同的size和scale。

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets

+ (UIImage *)animatedResizableImageNamed:(NSString *)name
                               capInsets:(UIEdgeInsets)capInsets
                            resizingMode:(UIImageResizingMode)resizingMode
                                duration:(NSTimeInterval)duration

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets
                            resizingMode:(UIImageResizingMode)resizingMode

　　图像的resizingMode 默认为UIImageResizingModeTile。当想要使用UIImageResizingModeStretch时，才调用该方法。

- (UIImage *)imageWithRenderingMode:(UIImageRenderingMode)renderingMode

- (UIImage *)imageFlippedForRightToLeftLayoutDirection

　　水平翻转图像。

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初始化UIImage对象：

- (instancetype)initWithContentsOfFile:(NSString *)path

　　path：文件的路径，应包含扩展名。

　　该方法将图像加载入内存并标记为purgeable。如果需要加载图像数据时但已被清除，图像对象会再次从指定的路径加载数据。

- (instancetype)initWithData:(NSData *)data

- (instancetype)initWithData:(NSData *)data
                       scale:(CGFloat)scale

- (instancetype)initWithCGImage:(CGImageRef)CGImage

- (instancetype)initWithCGImage:(CGImageRef)imageRef
                          scale:(CGFloat)scale
                    orientation:(UIImageOrientation)orientation

- (instancetype)initWithCIImage:(CIImage *)ciImage
- (instancetype)initWithCIImage:(CIImage *)ciImage
                          scale:(CGFloat)scale
                    orientation:(UIImageOrientation)orientation

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图像对象的属性：

@property(nonatomic, readonly) UIImageOrientation imageOrientation

typedef enum {

UIImageOrientationUp,

UIImageOrientationDown ,   // 180 deg rotation

UIImageOrientationLeft ,   // 90 deg CW

UIImageOrientationRight ,   // 90 deg CCW

UIImageOrientationUpMirrored ,    // as above but image mirrored along

// other axis. horizontal flip

UIImageOrientationDownMirrored ,  // horizontal flip

UIImageOrientationLeftMirrored ,  // vertical flip

UIImageOrientationRightMirrored , // vertical flip

} UIImageOrientation;

@property(nonatomic, readonly) CGSize size

　　size反应了图像以point测量的逻辑大小。

@property(nonatomic, readonly) CGFloat scale

　　如果加载的图像文件名包括@2x，scale则为2.0。其他图像都假设其scale为1.0。

　　size * scale 可获得图像的像素大小。

@property(nonatomic, readonly) BOOL flipsForRightToLeftLayoutDirection

@property(nonatomic, readonly) UIImageResizingMode resizingMode

typedef enum {

UIImageResizingModeTile,

UIImageResizingModeStretch,

} UIImageResizingMode;

@property(nonatomic, readonly) CGImageRef CGImage

@property(nonatomic, readonly) CIImage *CIImage

@property(nonatomic, readonly) NSArray <UIImage *> *images

　　对于non-animated图像，images的值为nil。

@property(nonatomic, readonly) NSTimeInterval duration

　　对于non-animated图像，duration的值为0.0。

@property(nonatomic, readonly) UIEdgeInsets capInsets

@property(nonatomic, readonly) UIEdgeInsets alignmentRectInsets

@property(nonatomic, readonly) UIImageAsset *imageAsset

@property(nonatomic, readonly, copy) UITraitCollection *traitCollection

@property(nonatomic, readonly) UIImageRenderingMode renderingMode

typedef enum : NSInteger {

UIImageRenderingModeAutomatic,

UIImageRenderingModeAlwaysOriginal,

UIImageRenderingModeAlwaysTemplate,

information

} UIImageRenderingMode;

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绘制图像：

- (void)drawAtPoint:(CGPoint)point

　　point：图像的左上角。

　　该方法绘制的图像完全不透明，并使用kCGBlendModeNormal 混合模式。

- (void)drawAtPoint:(CGPoint)point
          blendMode:(CGBlendMode)blendMode
              alpha:(CGFloat)alpha

- (void)drawInRect:(CGRect)rect

- (void)drawInRect:(CGRect)rect
         blendMode:(CGBlendMode)blendMode
             alpha:(CGFloat)alpha

- (void)drawAsPatternInRect:(CGRect)rect