IOS 获取网络图片大小实例详解

ios 获取网络图片大小实例详解

　在ios开发过程中经常需要通过网络请求加载图片，有时，需要在创建uiimageview或uibutton来显示图片之前需要提前知道图片的尺寸，根据图片尺寸创建对应大小的控件。但是对于网络图片来说，要想通过最优的方法获得尺寸就略微有点困难，大体思路就是下面这种：

如果有使用sdwebimage，则首先检查是否缓存过该图片，如果没有，先通过文件头获取图片大小(针对格式为png、gif、jpg文件获取其尺寸大小)，如果获取失败，则下载完整的图片data，然后计算大小，如果有使用sdwebimage，则使用sdwebimage缓存该图片。

实例代码：

+(cgsize)downloadimagesizewithurl:(id)imageurl

{

  nsurl* url = nil;

  if([imageurl iskindofclass:[nsurl class]]){

    url = imageurl;

  }

  if([imageurl iskindofclass:[nsstring class]]){

    url = [nsurl urlwithstring:imageurl];

  }

  if(url == nil)

    return cgsizezero;

#ifdef dispatch_main_sync_safe

  if([[sdimagecache sharedimagecache] diskimageexistswithkey:absolutestring])

  {

    uiimage* image = [[sdimagecache sharedimagecache] imagefrommemorycacheforkey:absolutestring];

    if(!image)

    {

      nsdata* data = [[sdimagecache sharedimagecache] performselector:@selector(diskimagedatabysearchingallpathsforkey:) withobject:url.absolutestring];

      image = [uiimage imagewithdata:data];

    }

    if(image)

    {

      return image.size;

    }

  }

#endif

  nsmutableurlrequest *request = [[nsmutableurlrequest alloc]initwithurl:url cachepolicy:nsurlrequestuseprotocolcachepolicy timeoutinterval:1];

  

  nsstring* pathextendsion = [url.pathextension lowercasestring];

  cgsize size = cgsizezero;

  if ([pathextendsion rangeofstring:@"png"].location != nsnotfound) {

    size = [self downloadpngimagesizewithrequest:request];

  }

  else if([pathextendsion rangeofstring:@"gif"].location != nsnotfound)

  {

    size = [self downloadgifimagesizewithrequest:request];

  }

  else{

    size = [self downloadjpgimagesizewithrequest:request];

  }

  if(cgsizeequaltosize(cgsizezero, size))

  {

    nsdata* data = [nsdata datawithcontentsofurl:url];

    uiimage* image = [uiimage imagewithdata:data];

    if(image)

    {

      //如果未使用sdwebimage，则忽略；缓存该图片

#ifdef dispatch_main_sync_safe

      [[sdimagecache sharedimagecache] storeimage:image recalculatefromimage:yes imagedata:data forkey:url.absolutestring todisk:yes];

#endif

      size = image.size;

    }

  }

  //过滤掉不符合大小的图片，大图太大浪费流量，用户体验不好

  if (size.height > 2048 || size.height <= 0 || size.width > 2048 || size.width <= 0 ) {

    return cgsizezero;

  }

  else

  {

    return size;

  }

}

+(cgsize)downloadpngimagesizewithrequest:(nsmutableurlrequest*)request

{

  [request setvalue:@"bytes=16-23" forhttpheaderfield:@"range"];

  nsdata* data = [nsurlconnection sendsynchronousrequest:request returningresponse:nil error:nil];

  if(data.length == 8)

  {

    int w1 = 0, w2 = 0, w3 = 0, w4 = 0;

    [data getbytes:&w1 range:nsmakerange(0, 1)];

    [data getbytes:&w2 range:nsmakerange(1, 1)];

    [data getbytes:&w3 range:nsmakerange(2, 1)];

    [data getbytes:&w4 range:nsmakerange(3, 1)];

    int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;

    int h1 = 0, h2 = 0, h3 = 0, h4 = 0;

    [data getbytes:&h1 range:nsmakerange(4, 1)];

    [data getbytes:&h2 range:nsmakerange(5, 1)];

    [data getbytes:&h3 range:nsmakerange(6, 1)];

    [data getbytes:&h4 range:nsmakerange(7, 1)];

    int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;

    return cgsizemake(w, h);

  }

  return cgsizezero;

} 

+(cgsize)downloadgifimagesizewithrequest:(nsmutableurlrequest*)request

{

  [request setvalue:@"bytes=6-9" forhttpheaderfield:@"range"];

  nsdata* data = [nsurlconnection sendsynchronousrequest:request returningresponse:nil error:nil];

  if(data.length == 4)

  {

    short w1 = 0, w2 = 0;

    [data getbytes:&w1 range:nsmakerange(0, 1)];

    [data getbytes:&w2 range:nsmakerange(1, 1)];

    short w = w1 + (w2 << 8);

    short h1 = 0, h2 = 0;

    [data getbytes:&h1 range:nsmakerange(2, 1)];

    [data getbytes:&h2 range:nsmakerange(3, 1)];

    short h = h1 + (h2 << 8);

    return cgsizemake(w, h);

  }

  return cgsizezero;

} 

+(cgsize)downloadjpgimagesizewithrequest:(nsmutableurlrequest*)request

{

  [request setvalue:@"bytes=0-209" forhttpheaderfield:@"range"];

  nsdata* data = [nsurlconnection sendsynchronousrequest:request returningresponse:nil error:nil];

  

  if ([data length] <= 0x58) {

    return cgsizezero;

  }

  if ([data length] < 210) {// 肯定只有一个dqt字段

    short w1 = 0, w2 = 0;

    [data getbytes:&w1 range:nsmakerange(0x60, 0x1)];

    [data getbytes:&w2 range:nsmakerange(0x61, 0x1)];

    short w = (w1 << 8) + w2;

    short h1 = 0, h2 = 0;

    [data getbytes:&h1 range:nsmakerange(0x5e, 0x1)];

    [data getbytes:&h2 range:nsmakerange(0x5f, 0x1)];

    short h = (h1 << 8) + h2;

    return cgsizemake(w, h);

  } else {

    short word = 0x0;

    [data getbytes:&word range:nsmakerange(0x15, 0x1)];

    if (word == 0xdb) {

      [data getbytes:&word range:nsmakerange(0x5a, 0x1)];

      if (word == 0xdb) {// 两个dqt字段

        short w1 = 0, w2 = 0;

        [data getbytes:&w1 range:nsmakerange(0xa5, 0x1)];

        [data getbytes:&w2 range:nsmakerange(0xa6, 0x1)];

        short w = (w1 << 8) + w2;

        short h1 = 0, h2 = 0;

        [data getbytes:&h1 range:nsmakerange(0xa3, 0x1)];

        [data getbytes:&h2 range:nsmakerange(0xa4, 0x1)];

        short h = (h1 << 8) + h2;

        return cgsizemake(w, h);

      } else {// 一个dqt字段

        short w1 = 0, w2 = 0;

        [data getbytes:&w1 range:nsmakerange(0x60, 0x1)];

        [data getbytes:&w2 range:nsmakerange(0x61, 0x1)];

        short w = (w1 << 8) + w2;

        short h1 = 0, h2 = 0;

        [data getbytes:&h1 range:nsmakerange(0x5e, 0x1)];

        [data getbytes:&h2 range:nsmakerange(0x5f, 0x1)];

        short h = (h1 << 8) + h2;

        return cgsizemake(w, h);

      }

    } else {

      return cgsizezero;

    }

  }

}

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