Question

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

我正在尝试关注O'Reilly的书，iPhone游戏开发，但是在第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 page，这是书中未经证实的勘误表。该行可以替换哪些功能代码？

其他详细信息

可以下载示例项目here。

我在渲染函数中遇到错误，按照第72页到第73页的书中的说明，在gsMain.m的渲染函数中构建gsMain类（它与示例项目pg77不同）

本书指示构建gsMain类的代码片段如下：

//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应该显示第71页到第77页的练习结果，但它与71到77中给出的给定指令非常不同。以下代码是从上面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

[ [ UIColor grayColor ] CGColor ]怎么样？

您使用的是最新的SDK吗？我假设您的UIColor.h标头有CGColor的属性？（我会检查你的SDK设置 - 当我打开示例项目时，它被设置为iOS 3.x）

在Swift 3.x中：UIColor.gray.cgColor

Answer 2

我为Simulator 3.1.3编译了p77示例，并没有遇到任何编译器警告或错误。

代码：

- (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]]];

    //...
}

似乎编译好了。也许您可以指定您正在编译的三个示例中的哪一个以及目标OS版本？

Answer 3

确保#include <UIKit/UIKit.h>。

它是-grayColor，而不是-greyColor。

如何在CGContextSetFillColorWithColor中访问UIColor的CGColor属性？

3 个答案: