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轉自：http://blog.csdn.net/likendsl/article/details/7662739
1. UIImageView不支持內部圖片平鋪(tile)
2. 資源中的圖片要用小寫的,模擬器中可能不區分大小寫,但在真機中區分 .
?? [UIImage imageNamed:@""]; 在設備中區分大小寫
3. UIView沒有背景圖屬性,有背景色屬性.設置背景圖可以用addSubView(backgroundImage);，推薦的是設置背景色。
4. [UIImage imageNamed:@""];它是有緩存特性 的
?? + (UIImage *)imageWithContentsOfFile:(NSString?*)path;? //does not cache the image object.
?? imageNamed文檔解釋：
??This method looks?in the system caches for an image object? with the specified name and returns that object if it exists. If a matching image object is not already in the cache, this method loads the image data from the specified file, caches it, and then returns the resulting object.
? On a device running iOS 4 or later, the behavior is identical if the device’s screen has a scale of1.0. If the screen has a scale of2.0, this method first searches for an image file with the same filename with an@2xsuffix appended to it. For example, if the file’s name isbutton, it first searches forbutton@2x. If it finds a 2x, it loads that image and sets thescale?property of the returnedUIImage?object to2.0. Otherwise, it loads the unmodified filename and sets thescale?property to1.0.
?? On iOS 4 and later, the name of the file is not required to specify the filename extension. Prior to iOS 4, you must specify the filename extension.
??? 可能在多次操作之后，應用經常發生內存警告從而導致自動退出的問題。定位之后發現是由于[UIImage imageNamed: @""]分配的圖像都沒有釋放引起的。而之前從官方的reference中得到的信息應該是[UIImage imageNamed:@""]分配的圖像系統會放到cache里面。而關于cache管理的規則就沒有明確的介紹。由此看來[UIImage imageNamed:]只適合與UI界面中小的貼圖的讀取，而一些比較大的資源文件應該盡量避免使用這個接口。
?5. ?UIImage的 - (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight
?????指定兩個方向上不被縮放的部分。
???? 對應的 rightCapWidth = image.size.width - (image.leftCapWidth + 1);
??????????????? bottomCapHeight = image.size.height - (image.topCapHeight + 1);
???? leftCapWidth,rightCapWidth之間的，topCapHeight,bottomCapHeight之間的像素被平鋪以達到縮放效果。
???? 另外UIView.contentStretch在這里好像不起作用。
????? 注意：使用這個函數時，要取它的返回值。并且 That method could return nil?if the base image is less than 5 pixels wide or 5 pixels tall? since it needs the 4 pixels for the caps + 1 pixel to stretch.
示例：設置導航欄上的自定義返回按鈕
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[cpp] ?view plaincopy
-?(void )setNavigationBackButton?? {?? ????const ?int ?KLeftWidth=25;?? ????UIImage*?image=[[UIImage?imageNamed:@"back.png" ]?stretchableImageWithLeftCapWidth:KLeftWidth?topCapHeight:0];?? ????UIImage*?hightlightedImage=[[UIImage?imageNamed:@"back_pressed.png" ]?stretchableImageWithLeftCapWidth:KLeftWidth?topCapHeight:0];?? ????NSString*?text=[[[self.navigationController?viewControllers]?objectAtIndex:0]?navigationItem].title;?? ????UIFont*?font=[Utility?fontWithSize:12];?? ????CGSize?stringSize?=?[text?sizeWithFont:font];?? ????CGFloat?textWidth?=?stringSize.width+KLeftWidth;?? ?????? ????UIButton*?button=[UIViewUtil?createUIButtonWithImage:image?? ???????????????????????????????????????hightlightedImage:hightlightedImage???? ???????????????????????????????????????????selectedImage:nil?? ???????????????????????????????????????????????????title:text?? ??????????????????????????????????????????????titleColor:color(0x33,0x33,0x33)?? ????????????????????????????????????????????????????posX:0?posY:0];?? ????button.titleLabel.font=[Utility?fontWithSize:12];?? ????CGRect?rect=button.frame;?? ????rect.size.width=textWidth;?? ????button.frame=rect;?? ????UIBarButtonItem*?buttonItem?=?[[UIBarButtonItem?alloc]?initWithCustomView:button];?? ????[button?addTarget:self?action:@selector(popViewControllerAnimated)?forControlEvents:UIControlEventTouchUpInside];?? ????[[self?navigationItem]?setLeftBarButtonItem:buttonItem];?? ????[buttonItem?release];?? ????[button?release];?????? }?? ?
6. 支持內置動畫，播放圖片序列。
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[cpp] ?view plaincopy
imageView.animationImages?=?imageArray;?? imageView.animationDuration?=?0.75f;?? [self.view?addSubview:imageView];?? [imageView?startAnimating];?? ?
7. UIImageView要設置self.userInteractionEnabled = YES才支持交互。
8.? 構建圖像的方式：
[cpp] ?view plaincopy
UIGraphicsBeginImageContext(CGSizeMake(SIDE_LENGTH,?SIDE_LENGTH));?? CGContextRef?context?=?UIGraphicsGetCurrentContext();?? ...?? UIImage?*theImage?=?UIGraphicsGetImageFromCurrentImageContext();?? ?? UIGraphicsEndImageContext();?? ?? return ?theImage;??9. 動態圖像，如gif，貌似 iphone不支持動態圖象，采用UIWebView替代顯示gif。
[cpp] ?view plaincopy
???(void )imagePickerController:(UIImagePickerController?*)picker?didFinishPickingMediaWithInfo:(NSDictionary?*)info?? ?? {?????? ?? ????????NSString*?referenceURL=[info?objectForKey:UIImagePickerControllerReferenceURL];?? ????????NSLog(@"%@" ,referenceURL);???? ?????????? ????????ALAssetsLibrary?*library?=?[[ALAssetsLibrary?alloc]?init];?? ?? ...?? }?? ?? #import?<AssetsLibrary/ALAssetsLibrary.h> ??#import?<AssetsLibrary/ALAssetRepresentation.h> ???? ?? 10. 保存圖片到相冊
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[cpp] ?view plaincopy
-(void )saveToPhotosAlbum?? {?? ????UIImage*?image=nil;?? ????NSObject*?obj=..;?? ????if ([obj?isKindOfClass:[UIImage?class ]])?? ????{?? ????????image=(UIImage*)obj;?? ????}?? ????else ?? ????{?? ????????image=[UIImage?imageWithData:(NSData?*)obj];?? ????}?? ?? ????if (image)?? ????{?? ????????UIImageWriteToSavedPhotosAlbum(image,self,@selector(image:didFinishSavingWithError:contextInfo:),?nil);??? ????}?? ????else ?? ????{?? ??????????? ????}?? }?? ?? #if?1?? ??-?(void )image:(UIImage?*)image?didFinishSavingWithError:(NSError?*)error?contextInfo:(void ?*)contextInfo???? {???? ????if ?(error?==?nil)???? ?????????? ????else ???? ????????? }???? #endif?? ??11. emoji表情
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emoji是日本開發的一字符編碼集，在iOS中集成了該字符集， 可以通過編程的方式判斷，開啟或關閉該功能。
已測試它可顯示于UILabel，UIButton，UIWebView，使用如“\ue415”的unicode碼。
http://pukupi.com/post/1964/
可結合NSString的draw方法，把表情畫到UIImage上：
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[cpp] ?view plaincopy
CGSize?size?=?[text?sizeWithFont:aFont];?? if ?(UIGraphicsBeginImageContextWithOptions?!=?NULL)??{?? ???UIGraphicsBeginImageContextWithOptions(size,NO,0.0);?? }?? else ??{?? ???UIGraphicsBeginImageContext(size);?? }?? [text?drawAtPoint:CGPointMake(0.0,?0.0)?withFont:aFont];?? UIImage?*image?=?UIGraphicsGetImageFromCurrentImageContext();?? UIGraphicsEndImageContext();?????? return ?image;??編程開啟iOS emoji，未測試成功。
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iOS5.1下emoji表情顯示方框的解決辦法? ??
在iOS5.1的部分設備上,emoji表情無法正常顯示.原因是iOS4上面的emoji用的是softbank的編碼,到iOS5以后,emoji被放進了Unicode6.0,導致原來的老編碼可能存在部分不兼容現象.
http://www.cocoachina.com/bbs/read.php?tid=96847&page=1
12. UIImagePickerController 拍照后，圖片旋轉了90度?？赡苓@個情況在5.0就不出現了。
[cpp] ?view plaincopy
#pragma?mark?UIImagePickerControllerDelegate ??-?(void )imagePickerController:(UIImagePickerController?*)picker?didFinishPickingMediaWithInfo:(NSDictionary?*)info?? {?? ????[picker?dismissModalViewControllerAnimated:YES];?? ?????? ????NSString*?mediaType=[info?objectForKey:UIImagePickerControllerMediaType];?? ????if ([mediaType?isEqualToString:(NSString*)kUTTypeImage])?? ????{?? ????????UIImage*?image=[info?objectForKey:UIImagePickerControllerOriginalImage];?? ????????UIImageOrientation?imageOrientation=image.imageOrientation;?? ????????if (imageOrientation!=UIImageOrientationUp)?? ????????{?? ?????????????? ?????????????? ????????????UIGraphicsBeginImageContext(image.size);?? ????????????[image?drawInRect:CGRectMake(0,?0,?image.size.width,?image.size.height)];?? ????????????iPortraitImageView.image?=?UIGraphicsGetImageFromCurrentImageContext();?? ????????????UIGraphicsEndImageContext();?? ?????????????? ????????}?? ????}?? }???? ?? ?? ?? UIImagePickerController*?pickerController?=?[[UIImagePickerController?alloc]?init];?? ????????pickerController.delegate?=?self;?? ????????pickerController.allowsEditing=YES;?? ?? ????????if (buttonIndex==0)?? ????????{?? ????????????if ([UIImagePickerController?isSourceTypeAvailable:UIImagePickerControllerSourceTypePhotoLibrary])?? ????????????{?? ????????????????pickerController.sourceType?=?UIImagePickerControllerSourceTypePhotoLibrary;?? ????????????}?? ????????}?? ????????else ?? ????????{?? ????????????if ([UIImagePickerController?isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])?? ????????????{?? ????????????????pickerController.sourceType?=?UIImagePickerControllerSourceTypeCamera;?? ????????????}?? ????????}?? ?????????? ????????[[UIViewUtil?firstAvailableUIViewControllerWithView:self]?presentModalViewController:pickerController?animated:YES];?? ????????[pickerController?release];?? ?? -?(void )imagePickerController:(UIImagePickerController?*)picker?didFinishPickingMediaWithInfo:(NSDictionary?*)info?? {?? ????[picker?dismissModalViewControllerAnimated:YES];?? ?????? ????NSString*?mediaType=[info?objectForKey:UIImagePickerControllerMediaType];?? ????if ([mediaType?isEqualToString:(NSString*)kUTTypeImage])?? ????{?? ????????UIImage*?image=[info?objectForKey:UIImagePickerControllerEditedImage];?? ????????iPortraitImageView.image=image;?? ????}?? }??? ?? 后面再次測試，結果測試每次拍照：?? ?? UIImage*?image=[info?objectForKey:UIImagePickerControllerOriginalImage];?? UIImageOrientation?imageOrientation=image.imageOrientation;?? ?? imageOrientation的值如左列，拍照時home鍵在位置為右列的值?? ?? UIImageOrientationRight?下?? UIImageOrientationUp????右?? UIImageOrientationDown??左?? UIImageOrientationLeft??上?? 若拍照多次后，出現黑屏，檢查是否有打印內容警告，同時看是否有上一次的拍照的圖片沒釋放。
13. ?對nil的image.size.width取值，結果可能不確定?？赡茉诖蠖鄶禉C器上取值為0，而有的機器上取到的是不確定值。
????? 所以一定要判斷如果為nil，width取值0。
14. 用圖片填充backgroundColor時，圖片上的透明區域可能為成為黑色。backgroundColor是隨內容大小而鋪的。
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15. 在資源目錄中，如果同時存在Icon.png 114x114像素，Icon@2x.png?114x114像素
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[java] ?view plaincopy
[image?imageNamed:@"Icon.png" ];??? ?? NSString*?path=[[NSBundle?mainBundle?]?pathForResource:@"Icon" ?ofType:@"png" ];?? [UIImage?imageWithContentsOfFile:path];?? ?? path=[[NSBundle?mainBundle?]?pathForResource:@"Icon@2x" ?ofType:@"png" ];?? UIImage?imageWithContentsOfFile:path];?? ?
在Documents中時，imageWithContentsOfFile的結果同上。
看樣子，對文件名中的@2x的識別，是UIImage在根據路徑找圖片后本身完成的，并且它是看最后使用的圖片名，而不一定是在路徑中指定的。
[java] ?view plaincopy
data=[NSData?dataWithContentsOfFile:path];?? image=[UIImage?imageWithData:data];對于Icon.png和Icon@2x .png，尺寸都是114 點，像素/點為1 :1 。?? ?
16. 圖片圓角化
?????http://www.cocoachina.com/bbs/read.php?tid=1757&page=1
17.? 給圖片加濾鏡
??????用Core Graphic的API，把圖片解析成RGBA四通道的位圖放入內存， 然后內存中有一個數組，數組中的每四個元素都是圖像上的一個像素點的RGBA的數值(0-255)，改變RGB的數值，再寫回去重新生成。
????? 變為黑白照片就是把每個像素點的RGB的值相加求平均值，再回寫回去。例如：R=B=G=100，就是灰色的，寫 for循環把每個像素點的RGB都改成各自的平均值，照片就變為黑白色了。如果圖像變為懷舊照片，就是底色發黃的，就是RG的比值調高，B保持不變，因為紅綠相配就是黃色。
??????http://www.cocoachina.com/bbs/read.php?tid=69525
??????http://www.cnblogs.com/leon19870907/articles/1978065.html
18.? ? 繪半透明矩形
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19. ? GPUImage
?????? https://github.com/BradLarson/GPUImage
?????? 先編譯framework目錄下GPUImage.xcodeproj，生成.a，再編譯examples下某個應用程序。
轉載于:https://www.cnblogs.com/yifanfenfei/archive/2012/09/04/2671109.html
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