Ios 通过文件URL远程获取图像文件维度

我正在使用Dropbox Core API，在寻找获取图像文件的方法时，我陷入了困境。我在设备上检索缩略图，但我需要知道图像的宽度和高度，以便对其进行修改

我绝对不想在手机上下载整个文件来检查它的尺寸。你有没有想过要耍什么花招。元数据中唯一的东西就是文件大小，这在我的例子中是非常无用的

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非常感谢。

我找到了答案。我使用UIImage类别，而不是通过URL下载部分文件。一旦获得足够的数据来定义大小，它就会停止下载

我做了一些测试，它下载了大约30KB来获取图片的尺寸，不管文件大小是300KB还是10MB，这都非常快

它可以用于任何图像文件，而不仅仅是Dropbox API

以下是类别的标题：

#import <UIKit/UIKit.h>

typedef void (^UIImageSizeRequestCompleted) (NSURL* imgURL, CGSize size);

@interface UIImage (RemoteSize)

+ (void) requestSizeFor: (NSURL*) imgURL completion: (UIImageSizeRequestCompleted) completion;

@end

#导入
typedef void（^UIImageSizeRequestCompleted）（NSURL*imgURL，CGSize）；
@接口UIImage（RemoteSize）
+（无效）请求大小用于：（NSURL*）完成图：（UIImageSizeRequestCompleted）完成图；
@结束

以下是源文件：

#import "UIImage+RemoteSize.h"
#import <objc/runtime.h>`

#import <objc/runtime.h>

static char *kSizeRequestDataKey = "NSURL.sizeRequestData";
static char *kSizeRequestTypeKey = "NSURL.sizeRequestType";
static char *kSizeRequestCompletionKey = "NSURL.sizeRequestCompletion";

typedef uint32_t dword;

@interface NSURL (RemoteSize)

@property (nonatomic, strong) NSMutableData* sizeRequestData;
@property (nonatomic, strong) NSString* sizeRequestType;
@property (nonatomic, copy) UIImageSizeRequestCompleted sizeRequestCompletion;

@end

@implementation NSURL (RemoteSize)

- (void) setSizeRequestCompletion: (UIImageSizeRequestCompleted) block {
objc_setAssociatedObject(self, &kSizeRequestCompletionKey, block, OBJC_ASSOCIATION_COPY);
}

- (UIImageSizeRequestCompleted) sizeRequestCompletion {
return objc_getAssociatedObject(self, &kSizeRequestCompletionKey);
}

- (void) setSizeRequestData:(NSMutableData *)sizeRequestData {
objc_setAssociatedObject(self, &kSizeRequestDataKey, sizeRequestData, OBJC_ASSOCIATION_RETAIN);
}

- (NSMutableData*) sizeRequestData {
return objc_getAssociatedObject(self, &kSizeRequestDataKey);
}

- (void) setSizeRequestType:(NSString *)sizeRequestType {
objc_setAssociatedObject(self, &kSizeRequestTypeKey, sizeRequestType, OBJC_ASSOCIATION_RETAIN);
}

- (NSString*) sizeRequestType {
return objc_getAssociatedObject(self, &kSizeRequestTypeKey);
}

#pragma mark - NSURLConnectionDelegate

- (void) connection: (NSURLConnection*) connection didReceiveResponse:(NSURLResponse *)response {
[self.sizeRequestData setLength: 0];    //Redirected => reset data
}

- (void) connection: (NSURLConnection*) connection didReceiveData:(NSData *)data {
NSMutableData* receivedData = self.sizeRequestData;

if( !receivedData ) {
    receivedData = [NSMutableData data];
    self.sizeRequestData = receivedData;
}

[receivedData appendData: data];

//Parse metadata
const unsigned char* cString = [receivedData bytes];
const NSInteger length = [receivedData length];
const char pngSignature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
const char bmpSignature[2] = {66, 77};
const char gifSignature[2] = {71, 73};
const char jpgSignature[2] = {255, 216};

if(!self.sizeRequestType ) {
    if( memcmp(pngSignature, cString, 8) == 0 ) {
        self.sizeRequestType = @"PNG";
    }
    else if( memcmp(bmpSignature, cString, 2) == 0 ) {
        self.sizeRequestType = @"BMP";
    }
    else if( memcmp(jpgSignature, cString, 2) == 0 ) {
        self.sizeRequestType = @"JPG";
    }
    else if( memcmp(gifSignature, cString, 2) == 0 ) {
        self.sizeRequestType = @"GIF";
    }
}

if( [self.sizeRequestType isEqualToString: @"PNG"] ) {
    char type[5];
    int offset = 8;

    dword chunkSize = 0;
    int chunkSizeSize = sizeof(chunkSize);

    if( offset+chunkSizeSize > length )
        return;

    memcpy(&chunkSize, cString+offset, chunkSizeSize);
    chunkSize = OSSwapInt32(chunkSize);
    offset += chunkSizeSize;

    if( offset + chunkSize > length )
        return;

    memcpy(&type, cString+offset, 4); type[4]='\0';
    offset += 4;

    if( strcmp(type, "IHDR") == 0 ) {   //Should always be first
        dword width = 0, height = 0;
        memcpy(&width, cString+offset, 4);
        offset += 4;
        width = OSSwapInt32(width);

        memcpy(&height, cString+offset, 4);
        offset += 4;
        height = OSSwapInt32(height);

        if( self.sizeRequestCompletion ) {
            self.sizeRequestCompletion(self, CGSizeMake(width, height));
        }

        self.sizeRequestCompletion = nil;

        [connection cancel];
    }
}
else if( [self.sizeRequestType isEqualToString: @"BMP"] ) {
    int offset = 18;
    dword width = 0, height = 0;
    memcpy(&width, cString+offset, 4);
    offset += 4;

    memcpy(&height, cString+offset, 4);
    offset += 4;

    if( self.sizeRequestCompletion ) {
        self.sizeRequestCompletion(self, CGSizeMake(width, height));
    }

    self.sizeRequestCompletion = nil;

    [connection cancel];
}
else if( [self.sizeRequestType isEqualToString: @"JPG"] ) {
    int offset = 4;
    dword block_length = cString[offset]*256 + cString[offset+1];

    while (offset<length) {
        offset += block_length;

        if( offset >= length )
            break;
        if( cString[offset] != 0xFF )
            break;
        if( cString[offset+1] == 0xC0 ||
           cString[offset+1] == 0xC1 ||
           cString[offset+1] == 0xC2 ||
           cString[offset+1] == 0xC3 ||
           cString[offset+1] == 0xC5 ||
           cString[offset+1] == 0xC6 ||
           cString[offset+1] == 0xC7 ||
           cString[offset+1] == 0xC9 ||
           cString[offset+1] == 0xCA ||
           cString[offset+1] == 0xCB ||
           cString[offset+1] == 0xCD ||
           cString[offset+1] == 0xCE ||
           cString[offset+1] == 0xCF ) {

            dword width = 0, height = 0;

            height = cString[offset+5]*256 + cString[offset+6];
            width = cString[offset+7]*256 + cString[offset+8];

            if( self.sizeRequestCompletion ) {
                self.sizeRequestCompletion(self, CGSizeMake(width, height));
            }

            self.sizeRequestCompletion = nil;

            [connection cancel];

        }
        else {
            offset += 2;
            block_length = cString[offset]*256 + cString[offset+1];
        }

    }
}
else if( [self.sizeRequestType isEqualToString: @"GIF"] ) {
    int offset = 6;
    dword width = 0, height = 0;
    memcpy(&width, cString+offset, 2);
    offset += 2;

    memcpy(&height, cString+offset, 2);
    offset += 2;

    if( self.sizeRequestCompletion ) {
        self.sizeRequestCompletion(self, CGSizeMake(width, height));
    }

    self.sizeRequestCompletion = nil;

    [connection cancel];
}
}

- (void) connection: (NSURLConnection*) connection didFailWithError:(NSError *)error {
if( self.sizeRequestCompletion )
    self.sizeRequestCompletion(self, CGSizeZero);
}

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
return cachedResponse;
}

- (void) connectionDidFinishLoading: (NSURLConnection *)connection {
// Basically, we failed to obtain the image size using metadata and the
// entire image was downloaded...

if(!self.sizeRequestData.length) {
    self.sizeRequestData = nil;
}
else {
    //Try parse to UIImage
    UIImage* image = [UIImage imageWithData: self.sizeRequestData];

    if( self.sizeRequestCompletion && image) {
        self.sizeRequestCompletion(self, [image size]);
        return;
    }
}

self.sizeRequestCompletion(self, CGSizeZero);
}

@end

@implementation UIImage (RemoteSize)

+ (void) requestSizeFor: (NSURL*) imgURL completion: (UIImageSizeRequestCompleted) completion {

if( [imgURL isFileURL] ) {
    //Load from file stream
}
else {
    imgURL.sizeRequestCompletion = completion;

    NSURLRequest* request = [NSURLRequest requestWithURL: imgURL];
    NSURLConnection* conn = [NSURLConnection connectionWithRequest: request delegate: imgURL];
    [conn scheduleInRunLoop: [NSRunLoop mainRunLoop] forMode: NSDefaultRunLoopMode];
    [conn start];
}
}

@end

#导入“UIImage+RemoteSize.h”
#进口`
#进口
静态字符*kSizeRequestDataKey=“NSURL.sizeRequestData”；
静态字符*kSizeRequestTypeKey=“NSURL.sizeRequestType”；
静态字符*kSizeRequestCompletionKey=“NSURL.sizeRequestCompletion”；
类型定义uint32_t dword；
@接口NSURL（RemoteSize）
@属性（非原子，强）NSMutableData*sizeRequestData；
@属性（非原子，强）NSString*sizeRequestType；
@属性（非原子，副本）UIImageSizeRequestCompleted SizeRequestCompleted；
@结束
@实现NSURL（RemoteSize）
-（void）setSizeRequestCompletion:（UIImageSizeRequestCompleted）块{
objc_setAssociatedObject（self，&ksizereRequestCompletionKey，block，objc_ASSOCIATION_COPY）；
}
-（UIImageSizeRequestCompleted）sizeRequestCompletion{
返回objc_getAssociatedObject（self和ksizereRequestCompletionKey）；
}
-（void）setSizeRequestData:（NSMutableData*）sizeRequestData{
objc_setAssociatedObject（self和kSizeRequestDataKey、sizeRequestData、objc_ASSOCIATION_RETAIN）；
}
-（NSMutableData*）大小请求数据{
返回objc_getAssociatedObject（self和ksizereRequestDataKey）；
}
-（void）setSizeRequestType:（NSString*）sizeRequestType{
objc_setAssociatedObject（self和kSizeRequestTypeKey、sizeRequestType、objc_ASSOCIATION_RETAIN）；
}
-（NSString*）sizeRequestType{
返回objc_getAssociatedObject（self和ksizereRequestTypeKey）；
}
#pragma标记-NSURLConnectionLegate
-（void）连接：（NSURLConnection*）连接DidReceiverResponse：（NSURResponse*）响应{
[self.sizeRequestData setLength:0]；//重定向=>重置数据
}
-（void）连接：（NSURLConnection*）连接didReceiveData:（NSData*）数据{
NSMutableData*receivedData=self.sizeRequestData；
如果（！receivedData）{
接收数据=[NSMutableData]；
self.sizeRequestData=receivedData；
}
[接收数据附录数据：数据]；
//分析元数据
const unsigned char*cString=[receivedData bytes]；
const NSInteger length=[receivedData length]；
const char pngSignature[8]={137,80,78,71,13,10,26,10}；
常量字符bmpSignature[2]={66,77}；
常量字符签名[2]={71,73}；
const char jpgSignature[2]={255，216}；
如果（！self.sizeRequestType）{
if（memcmp（pngSignature，cString，8）=0）{
self.sizeRequestType=@“PNG”；
}
else if（memcmp（bmpSignature，cString，2）=0）{
self.sizeRequestType=@“BMP”；
}
else if（memcmp（jpgSignature，cString，2）=0）{
self.sizeRequestType=@“JPG”；
}
else if（memcmp（gifSignature，cString，2）=0）{
self.sizeRequestType=@“GIF”；
}
}
if（[self.sizeRequestType IsequalString:@“PNG”]）{
字符类型[5]；
整数偏移=8；
dword chunkSize=0；
int chunkSizeSize=sizeof（chunkSize）；
如果（偏移量+块大小大小>长度）
返回；
memcpy（&chunkSize，cString+offset，chunkSizeSize）；
chunkSize=OSSwapInt32（chunkSize）；
偏移量+=chunkSizeSize；
如果（偏移量+块大小>长度）
返回；
memcpy（&type，cString+offset，4）；type[4]='\0'；
偏移量+=4；
if（strcmp（type，“IHDR”）==0）{//应始终位于第一位
dword宽度=0，高度=0；
memcpy（&width，cString+offset，4）；
偏移量+=4；
宽度=OSSwapInt32（宽度）；
memcpy（&height，cString+offset，4）；
偏移量+=4；
高度=OSSwapInt32（高度）；
if（self.sizeRequestCompletion）{
self.sizeRequestCompletion（self，CGSizeMake（宽度、高度））；
}
self.sizeRequestCompletion=nil；
[连接取消]；
}
}
else if（[self.sizeRequestType IsequalString:@“BMP”]）{
整数偏移=18；
dword宽度=0，高度=0；
memcpy（&width，cString+offset，4）；
偏移量+=4；
memcpy（&height，cString+offset，4）；
偏移量+=4；
if（self.sizeRequestCompletion）{
self.sizeRequestCompletion（self，CGSizeMake（宽度、高度））；
}
self.sizeRequestCompletion=nil；
[连接取消]；
}
else if（[self.sizeRequestType IsequalString:@“JPG”]）{
整数偏移=4；
dword块_长度=cString[offset]*256+cString[offset+1]；
while（偏移量=长度）
打破
如果（cString[偏移量]！=0xFF）
打破
如果（cString[偏移量+1]==0xC0||
cString[偏移量+1]==0xC1||
cString[偏移量+1]==0xC2||
cString[偏移量+1]==0xC3||
cString[偏移量+1]==0xC5||
cString[偏移量+1]==0xC6||
cString[偏移量+1]==0xC7||
cString[偏移量+1]==0xC9||
cString[offset+1]==0xCA||
cString[偏移量+1]==0xCB||
cString[offset+1]==0xCD||
cString[offset+1]==0xCE||
cString[偏移量+1]==0xCF）{
dword宽度=0，高度=0；