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Malloc到一个CGPoint指针,在访问时抛出EXC\u BAD\u访问

core-foundation uikit c iphone

3

kdbdallas · 技术社区 · 15 年前

(供参考: iPhone Application Programming Guide: Event Handling - Listing 3-6 )

问题代码非常简单:

CFMutableDictionaryRef touchBeginPoints;
UITouch *touch;

....

CGPoint *point = (CGPoint *)CFDictionaryGetValue(touchBeginPoints, touch);

if (point == NULL)
{
    point = (CGPoint *)malloc(sizeof(CGPoint));
    CFDictionarySetValue(touchBeginPoints, touch, point);
}

现在当程序进入 if malloc 进入 point

当它试图通过进入 CFDictionarySetValue 使应用程序崩溃的函数: Program received signal: âEXC_BAD_ACCESSâ.

马洛克 并通过变量/指针为: &point 然而,这仍然给了我一个机会 EXC_BAD_ACCESS .

3 回复 | 直到 15 年前

1

4

Dave DeLong 15 年前

肖恩的回答基本上是正确的。根据 the documentation for CFDictionarySetValue retain 价值取决于你的 CFMutableDictionaryRef 已设置。我猜当您创建可变字典(大概是使用 CFDictionaryCreateMutable() how to handle setting and removing values .

NULL

CFMutableDictionaryRef dict = CFDictionaryCreateMutable(NULL, 0, &kCFTypeDictionaryKeyCallBacks, NULL);

CGPoint * point = (CGPoint *)malloc(sizeof(CGPoint));
point->x = 42;
point->y = 42;

CFDictionarySetValue(dict, @"foo", point);


CGPoint * newPoint = CFDictionaryGetValue(dict, @"foo");
NSLog(@"%f, %f", newPoint->x, newPoint->y);

日志:

2010-06-17 11:32:47.942 EmptyFoundation[45294:a0f] 42.000000, 42.000000

2

Dave Dribin 15 年前

CGPoint是一个struct,而不是Objective-C/CF对象,因此您需要将它包装在 NSValue :

+ (NSValue *)valueWithPoint:(NSPoint)aPoint

http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSValue_Class/Reference/Reference.html#//apple_ref/occ/clm/NSValue/valueWithPoint :

3

1

Sean 15 年前