Memory usage upgrade

autorelease the bitmap context for clearing cache when memory warnings

@@ -13,49 +13,57 @@
 @implementation UIImage (ForceDecode)
 
 + (UIImage *)decodedImageWithImage:(UIImage *)image {
-    // do not decode animated images
-    if (image.images) { return image; }
-
-    CGImageRef imageRef = image.CGImage;
-
-    CGImageAlphaInfo alpha = CGImageGetAlphaInfo(imageRef);
-    BOOL anyAlpha = (alpha == kCGImageAlphaFirst ||
-                     alpha == kCGImageAlphaLast ||
-                     alpha == kCGImageAlphaPremultipliedFirst ||
-                     alpha == kCGImageAlphaPremultipliedLast);
-
-    if (anyAlpha) { return image; }
-
-    size_t width = CGImageGetWidth(imageRef);
-    size_t height = CGImageGetHeight(imageRef);
-
-    // current
-    CGColorSpaceModel imageColorSpaceModel = CGColorSpaceGetModel(CGImageGetColorSpace(imageRef));
-    CGColorSpaceRef colorspaceRef = CGImageGetColorSpace(imageRef);
+    // while downloading huge amount of images
+    // autorelease the bitmap context
+    // and all vars to help system to free memory
+    // when there are memory warning.
+    // on iOS7, do not forget to call
+    // [[SDImageCache sharedImageCache] clearMemory];
+    @autoreleasepool{
+        // do not decode animated images
+        if (image.images) { return image; }
     
-    bool unsupportedColorSpace = (imageColorSpaceModel == 0 || imageColorSpaceModel == -1 || imageColorSpaceModel == kCGColorSpaceModelIndexed);
-    if (unsupportedColorSpace)
-        colorspaceRef = CGColorSpaceCreateDeviceRGB();
-
-    CGContextRef context = CGBitmapContextCreate(NULL, width,
-                                                 height,
-                                                 CGImageGetBitsPerComponent(imageRef),
-                                                 0,
-                                                 colorspaceRef,
-                                                 kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedFirst);
-
-    // Draw the image into the context and retrieve the new image, which will now have an alpha layer
-    CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
-    CGImageRef imageRefWithAlpha = CGBitmapContextCreateImage(context);
-    UIImage *imageWithAlpha = [UIImage imageWithCGImage:imageRefWithAlpha];
-
-    if (unsupportedColorSpace)
-        CGColorSpaceRelease(colorspaceRef);
+        CGImageRef imageRef = image.CGImage;
+    
+        CGImageAlphaInfo alpha = CGImageGetAlphaInfo(imageRef);
+        BOOL anyAlpha = (alpha == kCGImageAlphaFirst ||
+                         alpha == kCGImageAlphaLast ||
+                         alpha == kCGImageAlphaPremultipliedFirst ||
+                         alpha == kCGImageAlphaPremultipliedLast);
+    
+        if (anyAlpha) { return image; }
+    
+        size_t width = CGImageGetWidth(imageRef);
+        size_t height = CGImageGetHeight(imageRef);
+    
+        // current
+        CGColorSpaceModel imageColorSpaceModel = CGColorSpaceGetModel(CGImageGetColorSpace(imageRef));
+        CGColorSpaceRef colorspaceRef = CGImageGetColorSpace(imageRef);
+        
+        bool unsupportedColorSpace = (imageColorSpaceModel == 0 || imageColorSpaceModel == -1 || imageColorSpaceModel == kCGColorSpaceModelIndexed);
+        if (unsupportedColorSpace)
+            colorspaceRef = CGColorSpaceCreateDeviceRGB();
+    
+        CGContextRef context = CGBitmapContextCreate(NULL, width,
+                                                     height,
+                                                     CGImageGetBitsPerComponent(imageRef),
+                                                     0,
+                                                     colorspaceRef,
+                                                     kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedFirst);
     
-    CGContextRelease(context);
-    CGImageRelease(imageRefWithAlpha);
+        // Draw the image into the context and retrieve the new image, which will now have an alpha layer
+        CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
+        CGImageRef imageRefWithAlpha = CGBitmapContextCreateImage(context);
+        UIImage *imageWithAlpha = [UIImage imageWithCGImage:imageRefWithAlpha];
     
-    return imageWithAlpha;
+        if (unsupportedColorSpace)
+            CGColorSpaceRelease(colorspaceRef);
+        
+        CGContextRelease(context);
+        CGImageRelease(imageRefWithAlpha);
+        
+        return imageWithAlpha;
+    }
 }
 
 @end