Objective-C/Cocoa/XCode 新手 : How to receive Notifications?

Question

我无法从 cocoa 编程书​​中找到一个可以工作的示例(我认为部分问题是 XCode 已经过时了)。除了在 IB 中建立适当的连接之外，它没有提到我必须做的任何特殊事情才能接收来自 NSTableView 的通知。该应用程序是一个带有用于用户输入的 NSTextField 的程序，当单击按钮时，NSSpeechSynthesizer 的实例将说出输入的行。我应该能够通过选择表格 View 上的一行来切换说话的声音。我可以单击，该应用程序在技术上可以工作，但我无法通过单击 GUI 上 NSTableView 上的一行来更改默认语音:

appdelegate.h:

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate,NSSpeechSynthesizerDelegate,NSTableViewDelegate>
{
    NSArray *_voices;
    NSSpeechSynthesizer *_speechSynth;
}

@property (assign) IBOutlet NSWindow *window;
@property (weak) IBOutlet NSTextField *textField;
@property (assign) IBOutlet NSTextField *text;

@property (assign) IBOutlet NSButton *_speakButton;
@property (assign) IBOutlet NSButton *_stopButton;

@property (assign) IBOutlet NSTableView *table;

-(IBAction)sayIt:(id)sender;
-(IBAction)stopIt:(id)sender;

@end

appdelegate.m:

#import "AppDelegate.h"

@implementation AppDelegate

@synthesize window = _window;
@synthesize textField = _textField;
@synthesize text = _text;
@synthesize _speakButton;
@synthesize _stopButton;

@synthesize table;

-(void)speechSynthesizer:(NSSpeechSynthesizer *)sender didFinishSpeaking:(BOOL)finishedSpeaking
{
    NSLog(@"finishedSpeaking=%d",finishedSpeaking);
    [_speakButton setEnabled:YES];
    [_stopButton setEnabled:NO];
    [table setEnabled:YES];
}

-(id)init
{
    NSLog(@"init called");
    self = [super init];
    if (self)
    {
        NSLog(@"init");
        _speechSynth = [[NSSpeechSynthesizer  alloc] initWithVoice:nil];
        [_speechSynth setDelegate:self];
        [_text setStringValue:@""];
        _voices = [NSSpeechSynthesizer availableVoices];
    }

    //I added this line myself as I was trying to figure it out
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(tableViewSelectionDidChange:) name:@"MyNotification" object:table];
    return self;
}
-(IBAction)sayIt:(id)sender
{
    NSString *string = [_textField stringValue];
    if([string length]==0)
    {
        NSLog(@"string from %@ is of zero-length",_textField);
        return;
    }
    [_speechSynth startSpeakingString:string];
    [_text setStringValue:[_speechSynth voice]];
    ...
}
-(IBAction)stopIt:(id)sender
{
    NSLog(@"stopping");
    ...
}
-(NSInteger)numberOfRowsInTableView:(NSTableView *)tv
{
    return (NSInteger)[_voices count];
}
-(id)tableView:(NSTableView *)tv
objectValueForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row
{
    NSString *v = [_voices objectAtIndex:row];
    NSDictionary *dict =[NSSpeechSynthesizer attributesForVoice:v];
    return [dict objectForKey:NSVoiceName];
}

-(void)tableViewSelectionDidChange:(NSNotification *)notification
{
    NSInteger row = [table selectedRow];
    if(row==-1) return;
    NSString *selectedVoice = [_voices objectAtIndex:row];
    [_speechSynth setVoice:selectedVoice];
    NSLog(@"new voice = %@",selectedVoice);
}

-(void)awakeFromNib
{
    NSLog(@"awakeFromNib");
    NSString *defaultVoice = [NSSpeechSynthesizer defaultVoice];
    NSInteger defaultRow = [_voices indexOfObject:defaultVoice];
    NSIndexSet *indices = [NSIndexSet indexSetWithIndex:defaultRow];
    [table selectRowIndexes:indices byExtendingSelection:NO];
    [table scrollRowToVisible:defaultRow];
}
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    NSLog(@"Appdidfinishlaunching called");
}

@end

我猜我的做法是错误的。我只需要有人为我指明正确的方向，让我明白这应该如何运作。

Answer 1

这里有几个可能的错误来源。

• 您可能忘记将 Nib 中的表格 View 作为其委托(delegate)挂接到应用委托(delegate)。

• 您可能忘记将 Nib 中的应用委托(delegate)作为其 textField 挂接到文本字段。

  (还有其他可能性(与将东西连接到 Nib 有关)，但我不会列出所有这些......)

• 如果您的目标确实是获取选择消息作为通知，那么此行是错误的:

  [[NSNotificationCenter defaultCenter] 
    addObserver:self selector:@selector(tableViewSelectionDidChange:) 
    name:@"MyNotification" object:table];
  

  此通知的名称不是@"MyNotification"；它是NSTableViewSelectionDidChangeNotification。