objective-c - __unsafe_unretained 代表不会建立

Question

我有来自 .h 文件的代码(片段):

#import <UIKit/UIKit.h>
#import "ILView.h"

/**
 * Controls the orientation of the picker
 */
typedef enum {
    ILHuePickerViewOrientationHorizontal     =   0,
    ILHuePickerViewOrientationVertical       =   1
} ILHuePickerViewOrientation;

@class ILHuePickerView;

/**
 * Hue picker delegate
 */
@protocol ILHuePickerViewDelegate

/**
 * Called when the user picks a new hue
 *
 * @param hue 0..1 The hue the user picked
 * @param picker The picker used
 */
-(void)huePicked:(float)hue picker:(ILHuePickerView *)picker;

@end

/**
 * Displays a gradient allowing the user to select a hue
 */
@interface ILHuePickerView : ILView {
    id<ILHuePickerViewDelegate> delegate;
    float hue;
    ILHuePickerViewOrientation pickerOrientation;
}

/**
 * Delegate
 */
//@property (assign, nonatomic) IBOutlet id<ILHuePickerViewDelegate> delegate;
@property (assign, nonatomic) IBOutlet __unsafe_unretained id<ILHuePickerViewDelegate> delegate;

/**
 * The current hue
 */
@property (assign, nonatomic) float hue;

.m 文件如下所示:

#import "ILHuePickerView.h"
#import "UIColor+GetHSB.h"

@interface ILHuePickerView(Private)

-(void)handleTouches:(NSSet *)touches withEvent:(UIEvent *)event;

@end

@implementation ILHuePickerView

@synthesize color, delegate, hue, pickerOrientation;

#pragma mark - Setup

-(void)setup
{
    [super setup];

我查看了类似案例的 SO，发现我需要在属性中放置“__unsafe_unretained”……我做到了(希望是正确的)，但它仍然在构建时失败。完整的错误信息是: Existing ivar 'delegate' for property 'delegate' with assign attribute must be __unsafe_unretained

我做错了什么？

Answer 1

正如错误消息告诉您的那样，ivar:

@interface ILHuePickerView : ILView {
    id<ILHuePickerViewDelegate> delegate;    // <-- This is the ivar

需要声明__unsafe_unretained:

__unsafe_unretained id<ILHuePickerViewDelegate> delegate;

不是属性:

@property (assign, nonatomic) IBOutlet id<ILHuePickerViewDelegate> delegate;

因为 ARC 所有权限定符不适用于属性；它们仅适用于变量。

由于 @synthesize 指令为您创建了 ivar(使用正确的 ARC 限定符)，但是，您可以跳过它的声明:

@interface ILHuePickerView : ILView 

/**
 * Delegate
 */
@property (assign, nonatomic) IBOutlet id<ILHuePickerViewDelegate> delegate;

// etc.

事实上，这是现在推荐的程序；见Defining Classes在 TOCPL 中。