Question

PrefMySpotsViewCtrl.h

@class Location;

@interface PrefMySpotsViewCtrl : NSViewController
{
  NSTextField *locationSearchInput;
  NSString * enteredLocation;

  Location *l;
}

@property (nonatomic, retain) IBOutlet NSTextField *locationSearchInput;
@property (nonatomic, retain) NSString *enteredLocation;

PrefMySpotsViewCtrl.m

#import "Location.h"


- (void) controlTextDidChange:(NSNotification *)aNotification
{
   enteredLocation = [locationSearchInput stringValue];
   NSLog(@"in class:%@", enteredLocation);
   [l searchLocation];
}

Location.h

@class PrefMySpotsViewCtrl;

@interface Location : NSObject

{
  PrefMySpotsViewCtrl *p;  
}

- (void) searchLocation;

Location.m

#import "Location.h"
#import "PrefMySpotsViewCtrl.h"

@implementation Location

- (void) searchLocation
{
   NSLog(@"out of class: %@", [p enteredLocation]);
}

用户输入a到locationSearchInput，这是输出

2012-09-30 10:18:12.915 MyApp[839:303] in class:
2012-09-30 10:18:12.917 MyApp[839:303] in class:a

永远不会执行

searchLocation方法。

如果我执行l = [[Location alloc] init];，则会执行searchLocation，但输出为null

2012-09-30 10:28:46.928 MyApp[880:303] in class:
2012-09-30 10:28:46.929 MyApp[880:303] out of class: (null)
2012-09-30 10:28:46.930 MyApp[880:303] in class:a
2012-09-30 10:28:46.931 MyApp[880:303] out of class: (null)

有什么想法吗？

感谢？

Answer 1

但问题是：您是否已将有效的控制器实例（PrefMySpotsViewCtrl）分配给位置对象？

我的意思是：

l = [[Location alloc] init];
l->p = self;
[l searchLocation];

请记住，最好将PrefMySpotsViewCtrl声明为Location声明中的属性，如下所示：

@interface Location : NSObject
{
  PrefMySpotsViewCtrl *p;  
}
@property (nonatomic, assign) PrefMySpotsViewCtrl *p;

然后使用属性setter分配它：

l = [[Location alloc] init];
l.p = self;
[l searchLocation];

修改

由于下面的评论似乎OP不理解逻辑，我发布一个简单的例子让他更好地理解：

1）ClassA声明：

@interface ClassA : NSObject @property(nonatomic,retain) NSString *ABC; @end

2）ClassB声明：

@interface ClassB : NSObject @property(nonatomic,assign) ClassA *p; -(void) printClassAvar; @end @implementation ClassB -(void) printClassAvar { NSLog(@"Variable = %@", [self.p ABC]); } @end

3）用法：

ClassA *a = [ClassA new]; a.ABC = @"XZY"; ClassB *b = [ClassB new]; b.p = a; [b printClassAvar];

Answer 2

您尚未展示您的初始化方法。

您可能实际上没有为l创建iVar。就像这样：

// in the view controllers `initWithNibName:bundle:` method
l = [Location alloc] init]; // or whatever the inititializer for a Location object is.

因为你还没有创建l类型的对象，所以它是nil（无论如何都使用较新的LLVM编译器），并且它不会接收消息，所以永远不会调用你的方法。 / p>

目标C：方法和实例变量

2 个答案: