NValue存放的数据

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NSValue仅仅存放的是地址

如何在数据结构中存入C 结构体数据

在使用cocos2d时候发现需要将CGPoint存入数组中，而数组接受的类型是 id。为了解决这个问题，下面使用NSDictionary作为演示。
解决方案是使用 NSValue 进行转换，它有两个函数供使用，
1 valueWithPoint：转换CGPoint和NSPoint 为NSValue;
2 valueWithPointer:转换任何C数据结构为NSValue
这样就可以使用NSValue来代替C结构体数据存入数据结构了。
相应的从NSValue中获取数据的函数分别是 pointValue 和 pointerValue。
具体的样例代码如下：
复制代码

//Test.h#import <Foundation/Foundation.h>
@interface Test : NSObject {
NSMutableDictionary* dictionary;
CGPoint point1;
}
@property (nonatomic, retain) NSMutableDictionary* dictionary;
-(void)test;
@end

复制代码

//Test.m@implementation Test
@synthesize dictionary=dictionary;
-(id)init
{
if ((self = [super init])) {
dictionary = [[NSMutableDictionary alloc] init];
}
return self;
}
-(void)test
{
CGPoint point = CGPointMake(1.0f, 2.0f);
NSValue* value = [NSValue valueWithPoint:point];
[dictionary setObject:value forKey:@"point"];
point1 = CGPointMake(3.0f, 4.0f);
NSValue* value1 = [NSValue valueWithPointer:&point1];
[dictionary setObject:value1 forKey:@"point1"];
CGPoint point2 = CGPointMake(5.0f, 6.0f);
NSValue* value2 = [NSValue valueWithPointer:&point2];
[dictionary setObject:value2 forKey:@"point2"];
CGPoint* point3 = (CGPoint*)malloc(sizeof(CGPoint));
point3->x = 7.0f;
point3->y = 8.0f;
NSValue* value3 = [NSValue valueWithPointer:point3];
[dictionary setObject:value3 forKey:@"point3"];
}
-(void)dealloc
{
[dictionary release];
dictionary = nil;
[super dealloc];
}
@end

复制代码

//main.m#import <Foundation/Foundation.h>
#import "Test.h"
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// insert code here...
NSLog(@"Hello, World!");
Test* test = [[Test alloc] init];
[test test];
NSValue* val = [test.dictionary valueForKey:@"point"];
CGPoint p = [val pointValue];
NSLog(@"point x = %f, y = %f", p.x, p.y);
val = [test.dictionary valueForKey:@"point1"];
CGPoint p1 = *(CGPoint*)[val pointerValue];
NSLog(@"point1 x = %f, y = %f", p1.x, p1.y);
val = [test.dictionary valueForKey:@"point2"];
CGPoint p2 = *(CGPoint*)[val pointerValue];
NSLog(@"point2 x = %f, y = %f", p2.x, p2.y);
val = [test.dictionary valueForKey:@"point3"];
CGPoint* p3 = [val pointerValue];
NSLog(@"point2 x = %f, y = %f", p3->x, p3->y);
free(p3);
p3 = NULL;
[pool drain];
return 0;
}

输出结果如下：

2011-12-15 02:09:53.261 TestNSValue[2157:903] Hello, World!
2011-12-15 02:09:53.267 TestNSValue[2157:903] point x = 1.000000, y = 2.000000
2011-12-15 02:09:53.268 TestNSValue[2157:903] point1 x = 3.000000, y = 4.000000
2011-12-15 02:09:53.268 TestNSValue[2157:903] point2 x = 0.000000, y = 0.000000
2011-12-15 02:09:53.269 TestNSValue[2157:903] point3 x = 7.000000, y = 8.000000

注意：point2 的数据是有问题的因为 point2的内存在test函数中已经释放了，这说明NSValue仅仅存放的是地址而已。
point1 是Test类的成员变量所以内存一直都在数据是正确的。
point3 是使用malloc分配内存的所以也是正确的，别忘记在main中free掉。