iOS的imageIO加载和获取exif iOS开发中用imageIO渐进加载图片及获取exif的方法

//
//  SvIncrementallyImage.m
//  SvIncrementallyImage
//
//  Created by  maple on 6/27/13.
//  Copyright (c) 2013 maple. All rights reserved.
//

#import "SvIncrementallyImage.h"
#import <ImageIO/ImageIO.h>
#import <CoreFoundation/CoreFoundation.h>

@interface SvIncrementallyImage () {
    NSURLRequest    *_request;
    NSURLConnection *_conn;
   
    CGImageSourceRef _incrementallyImgSource;
   
    NSMutableData   *_recieveData;
    long long       _expectedLeght;
    bool            _isLoadFinished;
}

@property (nonatomic, retain) UIImage *image;
@property (nonatomic, retain) UIImage *thumbImage;

@end

@implementation SvIncrementallyImage

@synthesize imageURL = _imageURL;
@synthesize image    = _image;
@synthesize thumbImage = _thumbImage;

- (id)initWithURL:(NSURL *)imageURL
{
    self = [super init];
    if (self) {
        _imageURL = [imageURL retain];
       
        _request = [[NSURLRequest alloc] initWithURL:_imageURL];
        _conn    = [[NSURLConnection alloc] initWithRequest:_request delegate:self];
       
        _incrementallyImgSource = CGImageSourceCreateIncremental(NULL);
       
        _recieveData = [[NSMutableData alloc] init];
        _isLoadFinished = false;
    }
   
    return self;
}

#pragma mark -
#pragma mark NSURLConnectionDataDelegate

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    _expectedLeght = response.expectedContentLength;
    NSLog(@"expected Length: %lld", _expectedLeght);
   
    NSString *mimeType = response.MIMEType;
    NSLog(@"MIME TYPE %@", mimeType);
   
    NSArray *arr = [mimeType componentsSeparatedByString:@"/"];
    if (arr.count < 1 || ![[arr objectAtIndex:0] isEqual:@"image"]) {
        NSLog(@"not a image url");
        [connection cancel];
        [_conn release]; _conn = nil;
    }
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"Connection %@ error, error info: %@", connection, error);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"Connection Loading Finished!!!");
   
    // if download image data not complete, create final image
    if (!_isLoadFinished) {
        CGImageSourceUpdateData(_incrementallyImgSource, (CFDataRef)_recieveData, _isLoadFinished);
        CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyImgSource, 0, NULL);
        self.image = [UIImage imageWithCGImage:imageRef];
        CGImageRelease(imageRef);
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [_recieveData appendData:data];
   
    _isLoadFinished = false;
    if (_expectedLeght == _recieveData.length) {
        _isLoadFinished = true;
    }
   
    CGImageSourceUpdateData(_incrementallyImgSource, (CFDataRef)_recieveData, _isLoadFinished);
    CGImageRef imageRef = CGImageSourceCreateImageAtIndex(_incrementallyImgSource, 0, NULL);
    self.image = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
}

@end

image property: {
    ColorModel = RGB;
    DPIHeight = 72;
    DPIWidth = 72;
    Depth = 8;
    Orientation = 6;
    PixelHeight = 2448;
    PixelWidth = 3264;
    "{Exif}" =     {
        ApertureValue = "2.526069";
        BrightnessValue = "-0.5140446";
        ColorSpace = 1;
        ComponentsConfiguration =         (
            1,
            2,
            3,
            0
        );
        DateTimeDigitized = "2013:06:24 22:11:30";
        DateTimeOriginal = "2013:06:24 22:11:30";
        ExifVersion =         (
            2,
            2,
            1
        );
        ExposureMode = 0;
        ExposureProgram = 2;
        ExposureTime = "0.06666667";
        FNumber = "2.4";
        Flash = 16;
        FlashPixVersion =         (
            1,
            0
        );
        FocalLenIn35mmFilm = 33;
        FocalLength = "4.13";
        ISOSpeedRatings =         (
            400
        );
        MeteringMode = 3;
        PixelXDimension = 3264;
        PixelYDimension = 2448;
        SceneCaptureType = 0;
        SensingMethod = 2;
        ShutterSpeedValue = "3.906905";
        SubjectArea =         (
            2815,
            1187,
            610,
            612
        );
        WhiteBalance = 0;
    };
    "{GPS}" =     {
        Altitude = "27.77328";
        AltitudeRef = 0;
        Latitude = "22.5645";
        LatitudeRef = N;
        Longitude = "113.8886666666667";
        LongitudeRef = E;
        TimeStamp = "14:11:23.36";
    };
    "{TIFF}" =     {
        DateTime = "2013:06:24 22:11:30";
        Make = Apple;
        Model = "iPhone 5";
        Orientation = 6;
        ResolutionUnit = 2;
        Software = "6.1.4";
        XResolution = 72;
        YResolution = 72;
        "_YCbCrPositioning" = 1;
    };
}

enum {
    exifOrientationUp = 1,      // UIImageOrientationUp
    exifOrientationDown = 3,    // UIImageOrientationDown
    exifOrientationLeft = 6,    // UIImageOrientationLeft
    exifOrientationRight = 8,   // UIImageOrientationRight
   
    // these four exifOrientation does not support by all camera, but IOS support these orientation
    exifOrientationUpMirrored = 2,          // UIImageOrientationUpMirrored
    exifOrientationDownMirrored = 4,        // UIImageOrientationDownMirrored
    exifOrientationLeftMirrored = 5,        // UIImageOrientationLeftMirrored
    exifOrientationRightMirrored = 7,       // UIImageOrientationRightMirrored
};
typedef NSInteger ExifOrientation;