问题描述
编译此代码时，我得到错误initializer元素不是编译时常量。谁能解释为什么？
When compiling this code, I get the error "initializer element is not a compile-time constant". Can anyone explain why?
#import "PreferencesController.h"
@implementation PreferencesController
- (id)init
{
self = [super init];
if (self) {
// Initialization code here.
}
return self;
}
NSImage* imageSegment = [[NSImage alloc] initWithContentsOfFile:@"/User/asd.jpg"];//error here
推荐答案
当你在函数范围之外定义一个变量时，到您的可执行文件。这意味着您只能使用常量值。因为你不知道编译时运行时环境的一切（可用的类，它们的结构是什么），所以在运行时之前不能创建目标c对象，除了常量字符串，结构并保证保持这种方式。你应该做的是将变量初始化为nil并使用 + initialize 创建图像。 initialize 是一个类方法，将在您的类上调用任何其他方法之前调用。
When you define a variable outside the scope of a function, that variable's value is actually written into your executable file. This means you can only use a constant value. Since you don't know everything about the runtime environment at compile time (which classes are available, what is their structure, etc.), you cannot create objective c objects until runtime, with the exception of constant strings, which are given a specific structure and guaranteed to stay that way. What you should do is initialize the variable to nil and use +initialize to create your image. initialize is a class method which will be called before any other method is called on your class.
示例： / p>
Example:
NSImage *imageSegment = nil;
+ (void)initialize {
if(!imageSegment)
imageSegment = [[NSImage alloc] initWithContentsOfFile:@"/User/asd.jpg"];
}
- (id)init {
self = [super init];
if (self) {
// Initialization code here.
}
return self;
}
这篇关于编译器错误：“初始化器元素不是编译时常量”的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！