Change the SDWebImageContextPDFPageNumber to use 0-indexed, which is less surprising

Author: dreampiggy

SDWebImagePDFCoder/Classes/SDImagePDFCoder.m

@@ -42,18 +42,13 @@ - (UIImage *)decodedImageWithData:(NSData *)data options:(SDImageCoderOptions *)
         return nil;
     }
 
-    NSUInteger pageNumber = 1;
+    NSUInteger pageNumber = 0;
     CGSize imageSize = CGSizeZero;
     BOOL preserveAspectRatio = YES;
     // Parse args
     SDWebImageContext *context = options[SDImageCoderWebImageContext];
     if (context[SDWebImageContextPDFPageNumber]) {
-        NSUInteger rawPageNumber = [context[SDWebImageContextPDFPageNumber] unsignedIntegerValue];
-        if (rawPageNumber == 0) {
-            // start with 1 index
-            rawPageNumber = 1;
-        }
-        pageNumber = rawPageNumber;
+        pageNumber = [context[SDWebImageContextPDFPageNumber] unsignedIntegerValue];
     }
     if (context[SDWebImageContextPDFImageSize]) {
         NSValue *sizeValue = context[SDWebImageContextPDFImageSize];
@@ -84,7 +79,6 @@ - (NSData *)encodedDataWithImage:(UIImage *)image format:(SDImageFormat)format o
 // Using Core Graphics to draw PDF but not PDFKit(iOS 11+/macOS 10.4+) to keep old firmware compatible
 - (UIImage *)sd_createPDFImageWithData:(nonnull NSData *)data pageNumber:(NSUInteger)pageNumber targetSize:(CGSize)targetSize preserveAspectRatio:(BOOL)preserveAspectRatio {
     NSParameterAssert(data);
-    NSParameterAssert(pageNumber > 0);
     UIImage *image;
 
 #if SD_MAC
@@ -93,8 +87,7 @@ - (UIImage *)sd_createPDFImageWithData:(nonnull NSData *)data pageNumber:(NSUInt
     if (!imageRep) {
         return nil;
     }
-    // NSPDFImageRep page is 0 index...
-    imageRep.currentPage = pageNumber - 1;
+    imageRep.currentPage = pageNumber
     image = [[NSImage alloc] initWithSize:imageRep.size];
     [image addRepresentation:imageRep];
 
@@ -110,7 +103,8 @@ - (UIImage *)sd_createPDFImageWithData:(nonnull NSData *)data pageNumber:(NSUInt
         return nil;
     }
 
-    CGPDFPageRef page = CGPDFDocumentGetPage(document, pageNumber);
+    // `CGPDFDocumentGetPage` page number is 1-indexed.
+    CGPDFPageRef page = CGPDFDocumentGetPage(document, pageNumber + 1);
     if (!page) {
         CGPDFDocumentRelease(document);
         return nil;

SDWebImagePDFCoder/Classes/SDWebImagePDFCoderDefine.h

@@ -10,8 +10,8 @@
 NS_ASSUME_NONNULL_BEGIN
 
 /**
- A unsigned interger raw value which specify the desired PDF image page number. Because PDF can contains mutiple pages. Attention the page number index is started with 1. (NSNumber)
- If you don't provide this value, or the value is out of [1,MAX], use 1 (the first page) instead.
+ A unsigned interger raw value which specify the desired PDF image page number. Because PDF can contains mutiple pages. The page number index is started with 0. (NSNumber)
+ If you don't provide this value, use 0 (the first page) instead.
  */
 FOUNDATION_EXPORT SDWebImageContextOption _Nonnull const SDWebImageContextPDFPageNumber;