xcode - NSOutlineView 的 IBOutlet 未指向有效实例

Question

我在 Xcode 中创建了一个新的 Cocoa 应用程序项目，然后将 NSOutlineView 和 NSTextView 对象添加到窗口上。这两个对象被子类化为 MyOutlineView 和 MyTextView。之后我为它们制作了两个导出并编写了如下代码。

我发现问题是应用程序在运行时有两个不同的 MyOutlineView 实例。工作(有效)大纲 View 实例不等于 myOutlineView 导出实例。我错过了什么？

//
//  AppDelegate.h

#import <Cocoa/Cocoa.h>
#import "MyOutlineView.h"
#import "MyTextView.h"

@interface AppDelegate : NSObject <NSApplicationDelegate>

@property (assign) IBOutlet NSWindow *window;
@property (weak) IBOutlet MyOutlineView *myOutlineView;
@property (unsafe_unretained) IBOutlet MyTextView *myTextView;

@end

//
//  AppDelegate.m

#import "AppDelegate.h"

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)n
{
    NSLog(@"AppDelegate.myOutlineView(INVALID)::%@", _myOutlineView);
    NSLog(@"AppDelegate.myTextView::%@", _myTextView);
}

@end

//
//  MyOutlineView.h

#import <Cocoa/Cocoa.h>

@interface MyOutlineView : NSOutlineView <NSOutlineViewDataSource>;

@end

//
//  MyOutlineView.m

#import "MyOutlineView.h"

@implementation MyOutlineView

- (id)initWithCoder:(NSCoder *)aDecoder
{
    // This method is called first.
    self = [super initWithCoder:aDecoder];
    NSLog(@"MyOutlineView initWithCoder(INVALID)::%@", self);
    return self;
}

- (id)initWithFrame:(NSRect)frame
{
    // This method is also called but through a different instance with first one.
    self = [super initWithFrame:frame];
    NSLog(@"MyOutlineView initWithFrame(valid)::%@", self);
    return self;
}

- (NSInteger)outlineView:(NSOutlineView *)outlineView numberOfChildrenOfItem:(id)item
{
    NSLog(@"MyOutlineView data source delegate(valid)::%@", self);
    return 0;
}

- (id)outlineView:(NSOutlineView *)outlineView child:(NSInteger)index ofItem:(id)item
{
    return nil;
}

- (BOOL)outlineView:(NSOutlineView *)outlineView isItemExpandable:(id)item
{
    return NO;
}

@end

//
//  MyTextView.h

#import <Cocoa/Cocoa.h>

@interface MyTextView : NSTextView

@end

//
//  MyTextView.m

#import "MyTextView.h"

@implementation MyTextView

- (id)initWithCoder:(NSCoder *)aDecoder
{
    // This method is called.
    self = [super initWithCoder:aDecoder];
    NSLog(@"MyTextView initWithCoder::%@", self);
    return self;
}

- (id)initWithFrame:(NSRect)frame
{
    // But this method is NOT called at all.
    self = [super initWithFrame:frame];
    NSLog(@"MyTextView initWithFrame::%@", self);
    return self;
}

@end

输出:

MyTextView initWithCoder::                 [MyTextView: 0x10013be80]
MyOutlineView initWithCoder(INVALID)::     [MyOutlineView: 0x10014bc90]
MyOutlineView initWithFrame(valid)::       [MyOutlineView: 0x1001604a0]
MyOutlineView data source delegate(valid)::[MyOutlineView: 0x1001604a0]
AppDelegate.myOutlineView(INVALID)::       [MyOutlineView: 0x10014bc90]
AppDelegate.myTextView::                   [MyTextView: 0x10013be80]

因此，我必须输入“AppDelegate.myOutlineView = self;”进入 MyOutletView 的实现，无论它调用 AppDelegate 的相关方法。看起来不太自然。

Answer 1

Xcode 似乎不允许您将大纲 View 的委托(delegate)或数据源设置为自身。

所以我猜你正在做这样的事情:

也就是说:实例化自定义大纲 View 类的第二个副本。

这是此设置的输出:

2012-09-26 14:11:34.511 testproj[30255:403] -[MyOutlineView initWithCoder:]
2012-09-26 14:11:34.531 testproj[30255:403] -[MyOutlineView initWithFrame:]

通过删除“我的大纲 View ”的额外(突出显示的)实例，initWithFrame: 行将消失。

要使大纲 View 拥有自己的委托(delegate)，请执行以下操作:

- (void) awakeFromNib {
    self.delegate = self;
}

也就是说，委托(delegate)模式的要点是避免子类化的需要。如果您确实需要大纲 View 子类，请尝试直接重写 NSOutlineView/NSTableView 方法，而不是使用委托(delegate)协议(protocol)。