如何在CGColor中访问UIColor的UIColor属性？

Question

CGContextSetFillColorWithColor(g, [UIColor greyColor].CGColor);

我试图遵循O‘’Reilly的书，iPhone游戏开发，但在第73页第3章我得到了这个错误：

error: request for member 'CGColor' in something not a structure or union

根据这本书的errata页面，这是书中一个未经证实的错误。那行可以用什么功能代码替换呢？

附加细节

示例项目可以下载这里。

我在呈现函数中遇到了错误，我按照书中从第72页到第73页的说明，在gsMain.m的呈现函数上构建gsMain类(它不同于示例项目pg77)。

本书指导构建gsMain类的代码片段如下所示：

//gsMain.h
@interface gsTest : GameState { }  
@end

//gsMain.m 
@implementation gsMain 

-(gsMain*) initWithFrame:(CGRect)frame andManager:(GameStateManager*)pManager 

    { 
        if (self = [super initWithFrame:frame andManager:pManager]) { 
        NSLog(@"gsTest init"); 
    } 
return self; 
} 

-(void) Render 
{ 
    CGContextRef g = UIGraphicsGetCurrentContext(); 
    //fill background with gray 
    CGContextSetFillColorWithColor(g, [UIColor greyColor].CGColor); //Error Occurs here
    CGContextFillRect(g, CGRectMake(0, 0, self.frame.size.width, 
    self.frame.size.height)); 
//draw text in black 
CGContextSetFillColorWithColor(g, [UIColor blackColor].CGColor); 
[@"O'Reilly Rules!" drawAtPoint:CGPointMake(10.0,20.0) 
        withFont:[UIFont systemFontOfSize:[UIFont systemFontSize]]]; 
} 
-(void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event 
{ 
    UITouch* touch = [touches anyObject]; 
    NSUInteger numTaps = [touch tapCount]; 
    //todo: implement touch event code here 
} 
@end

Chapter3_Example_p77应该显示从第71页到77页的练习结果，但是它与71到77页中给出的指示有很大的不同。下面的代码是从上述链接下载的已完成的可编译类。

//gsMain.h
#import <Foundation/Foundation.h>
#import "GameState.h"
@interface gsMain : GameState {

}

@end

//  gsMain.m
//  Example
//  Created by Joe Hogue and Paul Zirkle

#import "gsMain.h"
#import "gsTest.h"
#import "Test_FrameworkAppDelegate.h"

@implementation gsMain

-(gsMain*) initWithFrame:(CGRect)frame andManager:(GameStateManager*)pManager {
if (self = [super initWithFrame:frame andManager:pManager]) {
    //do initializations here.
}
return self;
}

- (void) Render {
[self setNeedsDisplay]; //this sets up a deferred call to drawRect.
}

- (void)drawRect:(CGRect)rect {
CGContextRef g = UIGraphicsGetCurrentContext();
//fill background with gray
CGContextSetFillColorWithColor(g, [UIColor grayColor].CGColor);
CGContextFillRect(g, CGRectMake(0, 0, self.frame.size.width, self.frame.size.height));
//draw text in black.
CGContextSetFillColorWithColor(g, [UIColor blackColor].CGColor);
[@"O'Reilly Rules!" drawAtPoint:CGPointMake(10.0, 20.0) withFont:
    [UIFont systemFontOfSize:   [UIFont systemFontSize]]];

//fps display from page 76 of iPhone Game Development
int FPS = [((Test_FrameworkAppDelegate*)m_pManager) getFramesPerSecond];
NSString* strFPS = [NSString stringWithFormat:@"%d", FPS];
[strFPS drawAtPoint:CGPointMake(10.0, 60.0) withFont:[UIFont systemFontOfSize:
    [UIFont systemFontSize]]];
}

//this is missing from the code listing on page 77.
-(void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event
{
    UITouch* touch = [touches anyObject];
    NSUInteger numTaps = [touch tapCount];
    if( numTaps > 1 ) {
    [m_pManager doStateChange:[gsTest class]];
}
}

@end

Answer 1

那[ [ UIColor grayColor ] CGColor ]呢

您正在使用最新的SDK吗？我假设您的UIColor.h头具有CGColor的属性？(我会检查您的SDK设置-当我打开示例项目时，它被设置为iOS 3.x)

在Swift 3.x：UIColor.gray.cgColor中

Answer 2

我为Simator3.1.3编译了p77示例，没有遇到任何编译器警告或错误。

守则：

- (void)drawRect:(CGRect)rect {
    CGContextRef g = UIGraphicsGetCurrentContext();
    //fill background with gray
    CGContextSetFillColorWithColor(g, [UIColor grayColor].CGColor);
    CGContextFillRect(g, CGRectMake(0, 0, self.frame.size.width, self.frame.size.height));
    //draw text in black.
    CGContextSetFillColorWithColor(g, [UIColor blackColor].CGColor);
    [@"O'Reilly Rules!" drawAtPoint:CGPointMake(10.0, 20.0) withFont:[UIFont systemFontOfSize:[UIFont systemFontSize]]];

    //...
}

好像编译好了。也许您可以指定您正在编译的三个示例中的哪个，以及针对哪个目标OS版本？

Answer 3

确保你的#include <UIKit/UIKit.h>。

这是-grayColor，而不是-greyColor。