Objective-C 实例状态问题

[silentwins]

抄了Cocoa的一个实例：

#import <Cocoa/Cocoa.h>

@interface ViewController : NSViewController
{
    NSSpeechSynthesizer* _speechSynth;
}
- (IBAction)stopIt:(id)sender;
- (IBAction)sayIt:(id)sender;
@property (weak) IBOutlet NSTextField *textField;

@end

#import "ViewController.h"

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // Do any additional setup after loading the view.
}


- (void)setRepresentedObject:(id)representedObject {
    [super setRepresentedObject:representedObject];

    // Update the view, if already loaded.
}

- (id)init {
    self = [super init];
    if (self) {
        // Logs can help the beginner understand what
        // is happening and hunt down bugs.
        NSLog(@"init");
        
        // Create a new instance of NSSpeechSynthesizer
        // with the default voice.
        _speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:@"com.apple.speech.synthesis.voice.Alex"];
                }
        return self;
}

- (IBAction)stopIt:(id)sender {
    NSLog(@"stopping");
    [_speechSynth stopSpeaking];
}

- (IBAction)sayIt:(id)sender {
    NSString *string = [_textField stringValue];
    // Is the string zero-length?
    if ([string length] == 0) {
        NSLog(@"string from %@ is of zero-length", _textField);
        return; }
    // _speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:nil];
    // [_speechSynth setVoice:@"com.apple.speech.synthesis.voice.Alex"];
    [_speechSynth startSpeakingString:string];
    while([NSSpeechSynthesizer isAnyApplicationSpeaking] == true) {}
    NSLog(@"Have started to say: %@", string);
}
@end

如果代码如现在所描述，代码到[_speechSynth startSpeakingString:string];这一行是发不出声音出来的，而且我调试到_speechSynth此时是nil;

如果把
// _speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:nil];
// [_speechSynth setVoice:@"com.apple.speech.synthesis.voice.Alex"];
[_speechSynth startSpeakingString:string];
前两行的注释取消掉，程序就能正常发出声音，此时_speechSynth也不为nil。

请教一下为什么会这样，_speechSynth为什么没有持久化？谢谢！

[wuzesong]

在初始化方法里面，你通过 _speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:@"com.apple.speech.synthesis.voice.Alex"]; 初始化了_speechSynth， 在 [_speechSynth startSpeakingString:string]; 的前面，你又通过 _speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:nil]; [_speechSynth setVoice:@"com.apple.speech.synthesis.voice.Alex"]; 这两行代码又对_speechSynth进行了赋值，如果你说注释掉这两行代码，就可以正常播放声音， 那么我觉得 [[NSSpeechSynthesizer alloc] initWithVoice:nil] 这个方法返回的就是个nil， 你可以点进 initWithVoice 这个构造方法里面去看下，看看里面是不是判断了后面的参数，如果参数为nil，也返回空对象（nil），才出现你说的这个问题，跟持久化没有关系。