今天我决定要使用 Xcode 为我的 Mac 编写屏幕保护程序，并希望在 C++ 中完成大部分繁重的工作。根据我以前混合C++和Objective-C++的经验，当您想在其中合并一些C++时，您只需要将.m源文件的扩展名更改为.mm。
但是，我遇到了一个烦人的问题。如果我制作一个 Xcode 屏幕保护程序项目并且除了将初始TestScreenSaverView.m文件重命名为TestScreenSaverView.mm之外什么都不做，屏幕保护程序从编译和链接正常到编译并在链接时遇到问题。请注意，除了更改文件的扩展名外，我没有添加任何新代码。以下是日志输出：
Showing Recent Issues
Check dependencies
Write auxiliary files
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver.hmap
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-generated-files.hmap
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-all-target-headers.hmap
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-own-target-headers.hmap
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-project-headers.hmap
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-all-non-framework-target-headers.hmap
/bin/mkdir -p /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64
write-file /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaver.LinkFileList
Create product structure
/bin/mkdir -p /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/TestScreensaver.saver/Contents
/bin/mkdir -p /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/TestScreensaver.saver/Contents/MacOS
ProcessInfoPlistFile /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/TestScreensaver.saver/Contents/Info.plist TestScreensaver/Info.plist
cd /Users/cjh/Documents/code/swift/TestScreensaver
builtin-infoPlistUtility /Users/cjh/Documents/code/swift/TestScreensaver/TestScreensaver/Info.plist -expandbuildsettings -platform macosx -o /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/TestScreensaver.saver/Contents/Info.plist
CompileC /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaverView.o TestScreensaver/TestScreensaverView.mm normal x86_64 objective-c++ com.apple.compilers.llvm.clang.1_0.compiler
cd /Users/cjh/Documents/code/swift/TestScreensaver
export LANG=en_US.US-ASCII
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x objective-c++ -arch x86_64 -fmessage-length=0 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -std=gnu++14 -stdlib=libc++ -fobjc-arc -fobjc-weak -fmodules -gmodules -fmodules-cache-path=/Users/cjh/Library/Developer/Xcode/DerivedData/ModuleCache.noindex -fmodules-prune-interval=86400 -fmodules-prune-after=345600 -fbuild-session-file=/Users/cjh/Library/Developer/Xcode/DerivedData/ModuleCache.noindex/Session.modulevalidation -fmodules-validate-once-per-build-session -Wnon-modular-include-in-framework-module -Werror=non-modular-include-in-framework-module -Wno-trigraphs -fpascal-strings -O0 -fno-common -Wno-missing-field-initializers -Wno-missing-prototypes -Werror=return-type -Wdocumentation -Wunreachable-code -Wno-implicit-atomic-properties -Werror=deprecated-objc-isa-usage -Werror=objc-root-class -Wno-arc-repeated-use-of-weak -Wimplicit-retain-self -Wno-non-virtual-dtor -Wno-overloaded-virtual -Wno-exit-time-destructors -Wduplicate-method-match -Wno-missing-braces -Wparentheses -Wswitch -Wunused-function -Wno-unused-label -Wno-unused-parameter -Wunused-variable -Wunused-value -Wempty-body -Wuninitialized -Wconditional-uninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-conversion -Wconstant-conversion -Wint-conversion -Wbool-conversion -Wenum-conversion -Wno-float-conversion -Wnon-literal-null-conversion -Wobjc-literal-conversion -Wshorten-64-to-32 -Wno-newline-eof -Wno-selector -Wno-strict-selector-match -Wundeclared-selector -Wdeprecated-implementations -Wno-c++11-extensions -DDEBUG=1 -DOBJC_OLD_DISPATCH_PROTOTYPES=0 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk -fasm-blocks -fstrict-aliasing -Wprotocol -Wdeprecated-declarations -Winvalid-offsetof -mmacosx-version-min=10.13 -g -fvisibility-inlines-hidden -Wno-sign-conversion -Winfinite-recursion -Wmove -Wcomma -Wblock-capture-autoreleasing -Wstrict-prototypes -Wrange-loop-analysis -Wunguarded-availability -index-store-path /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Index/DataStore -iquote /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-generated-files.hmap -I/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-own-target-headers.hmap -I/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-all-target-headers.hmap -iquote /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/TestScreensaver-project-headers.hmap -I/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/include -I/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/DerivedSources/x86_64 -I/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/DerivedSources -F/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug -MMD -MT dependencies -MF /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaverView.d --serialize-diagnostics /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaverView.dia -c /Users/cjh/Documents/code/swift/TestScreensaver/TestScreensaver/TestScreensaverView.mm -o /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaverView.o
Ld /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/TestScreensaver.saver/Contents/MacOS/TestScreensaver normal x86_64
cd /Users/cjh/Documents/code/swift/TestScreensaver
export MACOSX_DEPLOYMENT_TARGET=10.13
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -arch x86_64 -bundle -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk -L/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug -F/Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug -filelist /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaver.LinkFileList -mmacosx-version-min=10.13 -Xlinker -object_path_lto -Xlinker /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaver_lto.o -Xlinker -export_dynamic -Xlinker -no_deduplicate -stdlib=libc++ -fobjc-arc -fobjc-link-runtime -ObjC -lc++ -Xlinker -dependency_info -Xlinker /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Intermediates.noindex/TestScreensaver.build/Debug/TestScreensaver.build/Objects-normal/x86_64/TestScreensaver_dependency_info.dat -o /Users/cjh/Library/Developer/Xcode/DerivedData/TestScreensaver-dufowvmnhdeakfekvozrelyhhccq/Build/Products/Debug/TestScreensaver.saver/Contents/MacOS/TestScreensaver
Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_ScreenSaverView", referenced from:
_OBJC_CLASS_$_TestScreensaverView in TestScreensaverView.o
"_OBJC_METACLASS_$_ScreenSaverView", referenced from:
_OBJC_METACLASS_$_TestScreensaverView in TestScreensaverView.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Activity Log Complete 6/4/18, 2:06 PM
不太确定问题是什么，因为我以前从未遇到过问题。有没有人知道可能是什么问题？
为了完整起见，下面是项目初始化时使用的代码：
TestScreensaverView.h
//
// TestScreensaverView.h
// TestScreensaver
//
// Created by C. Howard on 6/4/18.
// Copyright © 2018 C. Howard. All rights reserved.
//
#import <ScreenSaver/ScreenSaver.h>
@interface TestScreensaverView : ScreenSaverView
@end
TestScreensaverView.mm(最初是TestScreensaverView.m(
//
// TestScreensaverView.m
// TestScreensaver
//
// Created by C. Howard on 6/4/18.
// Copyright © 2018 C. Howard. All rights reserved.
//
#import "TestScreensaverView.h"
@implementation TestScreensaverView
- (instancetype)initWithFrame:(NSRect)frame isPreview:(BOOL)isPreview
{
self = [super initWithFrame:frame isPreview:isPreview];
if (self) {
[self setAnimationTimeInterval:1/30.0];
}
return self;
}
- (void)startAnimation
{
[super startAnimation];
}
- (void)stopAnimation
{
[super stopAnimation];
}
- (void)drawRect:(NSRect)rect
{
[super drawRect:rect];
}
- (void)animateOneFrame
{
return;
}
- (BOOL)hasConfigureSheet
{
return NO;
}
- (NSWindow*)configureSheet
{
return nil;
}
@end
Obj-C 类ScreenSaverView的实现似乎丢失了，从错误消息中可以明显看出。 我没有在命令行中看到它在那里ld，但由于您发布了屏幕截图而不是从日志中复制粘贴，因此我无法搜索它，所以也许我错过了它。
编辑Hokay，我自己错过了重点，一路上对 OP 相当粗鲁，我现在已经深入了解了这一点，这很简单。
似乎您需要将ScreenSaverView框架添加到您的项目中，您可以按照此处的配方进行操作：
http://docs.onemobilesdk.aol.com/ios-ad-sdk/adding-frameworks-xcode.html
如果源文件按.m构建，为什么不需要这样做尚不清楚。 你会认为你总是需要它，但显然不是。 把它归结为史蒂夫乔布斯的精神，只是玩弄我们这些来自坟墓之外的凡人。