委托不触发方法

Question

我查看了其他代表问题，但没有任何好的现有答案。一切都应该正确设置，我可以看到我的滑块将更改日志中的值。由于某种原因，当我从 squareView 调用委托函数 numberOfSquaresInSquareView() 时，它永远不会触发，并且 squareView 委托调用仅返回 nil。我知道我已经相当接近了，因为这与我发现的一些课程非常匹配，但我认为我错过了一些东西。 changeSquareCount() 有效，我可以在日志中看到它保存了该值。

squareView.h

#import <Cocoa/Cocoa.h>

NS_ASSUME_NONNULL_BEGIN
@class SquareView;
@protocol SquareViewDelegate <NSObject>

- (NSNumber *)numberOfSquaresInSquareView:(SquareView *)squareView;

@end

@interface SquareView : NSView
@property (nonatomic, weak) id<SquareViewDelegate> delegate;

@end

NS_ASSUME_NONNULL_END

squareView.m

#import "SquareView.h"

@implementation SquareView
@synthesize delegate;

- (id)initWithFrame:(NSRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
    }
    return self;
}

- (void)drawRect:(NSRect)dirtyRect {
    [super drawRect:dirtyRect];
    NSLog(@"drawing rect");
    [[NSColor redColor]set];

    //NSNumber *num = ; //cound pass in nil, dont matter
    NSLog(@"squares to draw: %@", [delegate numberOfSquaresInSquareView:self]);
    // Drawing code here.
}

@end

AppController.h

#import <Foundation/Foundation.h>
#import "SquareView.h"
//@class SquareView;
NS_ASSUME_NONNULL_BEGIN

@interface AppController : NSObject <SquareViewDelegate>

@property (retain) IBOutlet SquareView *squareView;

- (IBAction)changeSquareCount:(id)sender;
@end

NS_ASSUME_NONNULL_END

AppController.m

#import "AppController.h"

@implementation AppController
{
    NSNumber *_squareCount;
}
@synthesize squareView = _squareView;
- (void)awakeFromNib
{
    [_squareView setDelegate:nil];
    _squareCount = @(10);
    [_squareView setNeedsDisplay:YES];
}

- (void)changeSquareCount:(id)sender
{
    _squareCount = @([sender intValue]);
    NSLog(@"square count stored: %@",_squareCount);
    [_squareView setNeedsDisplay:YES];
}
-(NSNumber *)numberOfSquaresInSquareView:(SquareView *) squareView
{
    NSLog(@"triggering numberOfSquaresInSquareView");
    return _squareCount;
}

@end

Answer 1

delegate

必须“保留”某处才能使其发挥作用。正如我在这里看到的，

SquareView

是

AppController

的子视图，

delegate

的工作方式与

SquareView <-> AppController

类似。在这种情况下，这是一种回调。但是，您将其分配给

nil

[_squareView setDelegate:nil]

它应该是：

_squareView.delegate = self;

这样，每次调用 SquareView 中的

drawRect

时，都会触发 AppController 中的

numberOfSquaresInSquareView

，在这种情况下，它会打印出来

要绘制的方块：10