iphonesimulator（找不到 SDK）xcode 中的错误

问：

一段时间以来，我一直在尝试解决这个问题。我尝试为模拟器构建的原因是在视网膜 4 英寸显示屏上获取屏幕截图，现在应用商店需要该显示屏。我正在用 unity 制作一个应用程序，我从论坛上看到人们成功地制作了模拟器构建。

在为 iphone/ipad 进行常规构建时，我没有任何错误，但是打开我的项目（在 unity 中它被标记为模拟器）并尝试将其构建到模拟器失败并出现链接器错误（见下文）。很明显.尽管在检查首选项时>下载，但所有模拟器都已安装。我可以手动启动模拟器"iphonesimulator (SDK not found)" message in Architecture -> Base SDK selection list

我是 iphone/ipad 开发的初学者，尤其是在 Xcode 中，我正在搜索有关此问题的论坛，但没有找到任何可以解决我的问题的东西。谁能为我指出正确的方向？我应该尝试什么，我应该在哪里寻找错误？

谢谢！

ld: warning: directory not found for option '-L"/Users/mirko/Dropbox/Unity'
ld: warning: directory not found for option '-LProjects/Project3D'
ld: warning: directory not found for option '-LProject/Project3D/Builds/iOS/S3D"'
ld: warning: directory not found for option '-L"/Users/mirko/Dropbox/Unity'
ld: warning: directory not found for option '-LProjects/Project3D'
ld: warning: directory not found for option '-LProject/Project3D/Builds/iOS/S3D/Libraries"'
0  0x10a87b098  __assert_rtn + 144
1  0x10a87e431  mach_o::relocatable::Section<x86>::addRelocFixup(mach_o::relocatable::Parser<x86>&, macho_relocation_info<Pointer32<LittleEndian> > const*) + 1781
2  0x10a88e636  mach_o::relocatable::Section<x86>::makeFixups(mach_o::relocatable::Parser<x86>&, mach_o::relocatable::Parser<x86>::CFI_CU_InfoArrays const&) + 90
3  0x10a88aaad  mach_o::relocatable::Parser<x86>::parse(mach_o::relocatable::ParserOptions const&) + 1433
4  0x10a8820c3  mach_o::relocatable::Parser<x86>::parse(unsigned char const*, unsigned long long, char const*, long, ld::File::Ordinal, mach_o::relocatable::ParserOptions const&) + 313
5  0x10a87faa1  mach_o::relocatable::parse(unsigned char const*, unsigned long long, char const*, long, ld::File::Ordinal, mach_o::relocatable::ParserOptions const&) + 149
6  0x10a8a033a  archive::File<x86>::makeObjectFileForMember(archive::File<x86>::Entry const*) const + 794
7  0x10a89fb50  archive::File<x86>::forEachAtom(ld::File::AtomHandler&) const + 198
8  0x10a8b176c  ld::tool::InputFiles::forEachInitialAtom(ld::File::AtomHandler&) + 420
9  0x10a8ba884  ld::tool::Resolver::resolve() + 44
10  0x10a87b380  main + 370
11  0x10a86ccd4  start + 52
A linker snapshot was created at:
    /tmp/Project3DSystem-2013-02-20-134511.ld-snapshot
ld: Assertion failed: (src.atom != NULL), function addRelocFixup, file /SourceCache/ld64/ld64-136/src/ld/parsers/macho_relocatable_file.cpp, line 5468.