xcode 为什么将 NSString 对象传递给 XCTAssertTrue 的“格式”参数会导致构建错误？
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Why does passing an NSString object to the "format" parameter of XCTAssertTrue cause a build error?
提问by akivajgordon
In attempting to use XCTest to test my application, I get a build error when doing the following:
在尝试使用 XCTest 测试我的应用程序时，我在执行以下操作时遇到构建错误：
#import <XCTest/XCTest.h>
@interface MyTests : XCTestCase
@end
@implementation MyTests
- (void)testExample
{
NSString *str = @"foo";
XCTAssertTrue(YES, str); // Parse issue: Expected ')'
}
@end
but I do notget a build error if I do this:
但如果我这样做，我不会收到构建错误：
#import <XCTest/XCTest.h>
@interface MyTests : XCTestCase
@end
@implementation MyTests
- (void)testExample
{
XCTAssertTrue(YES, @"foo"); // this is just fine...
}
@end
The build error that I get is:
我得到的构建错误是：
Parse issue: Expected ')'
and it puts an arrow under the "s" in "str".
并在“str”中的“s”下方放置一个箭头。
I discovered that I can remedy this by changing
我发现我可以通过改变来解决这个问题
XCTAssertTrue(YES, str)
to
到
XCTAssertTrue(YES, @"%@", str)
but I just cannot figure out why that makes a difference. Can somebody please explain why this is so?
但我就是不明白为什么这会有所作为。有人可以解释一下为什么会这样吗？
回答by Itai Ferber
The XCT...macros are written to accept format strings — the strings themselves are optional (so that writing XCTAssertTrue(YES)is valid), but they must be constant strings. You cannot pass objects into the macro without having a format string, which is why XCTAssertTrue(YES, @"%@", str)works, but, say, XCTAssertTrue(YES, str)or XCTAssertTrue(NO, nil)wouldn't.
该XCT...宏被写入接受格式字符串-字符串本身是可选的（这样写XCTAssertTrue(YES)是有效的），但必须是常量字符串。你不能在没有格式字符串的情况下将对象传递到宏中，这就是为什么XCTAssertTrue(YES, @"%@", str)有效，但是，XCTAssertTrue(YES, str)或者XCTAssertTrue(NO, nil)不会。
回答by Greg Parker
Deep inside the implementation, the code does this:
在实现的深处，代码是这样做的：
@"" format
If formatis a constant string literal, the compiler concatenates the strings. If formatis anything else, you get a compiler error.
如果format是常量字符串文字，编译器将连接字符串。如果format是其他任何事情，您会收到编译器错误。
回答by Jonathan Mitchell
Passing predefined text into the assertion is sometimes desirable so:
有时需要将预定义文本传递到断言中，因此：
XCTAssertTrue(YES, @"foo"); // this is just fine...
As is this
就像这个
#define FOO @"foo"
XCTAssertTrue(YES, FOO); // this is just fine too...
So I do stuff like:
所以我做这样的事情：
#define DBUEqualityTestFailed @"Equality test failed"
// test
DBNumber *n1 = [@((int)1) dbNumberFromIntValue];
XCTAssertTrue(*(int *)[n1 valuePointer] == 1, DBUEqualityTestFailed);
XCTAssertTrue([n1 valuePointer] == [n1 valuePointer], DBUEqualityTestFailed);
XCTAssertTrue(*(int *)[n1 valuePointer] == *(int *)[n1 valuePointer], DBUEqualityTestFailed);
