macOS中与剪切板相关的接口封装在框架<AppKit.framework>中，主要的类为NSPasteboard，类似iOS系统上的UIPasteboard。

通过接口[NSPasteboard generalPasteboard] 可以获取通用剪切板实例，这个实例为macOS所有App共用，App之间也是通过generalPasteboard来实现内容的复制粘贴。

1. 往剪切板写入内容：

NSString *text = [[NSString alloc] initWithUTF8String:@"demo text"];
// declareTypes接口实际上调用了clearContent接口
if (![[NSPasteboard generalPasteboard] declareTypes:@[NSPasteboardTypeString] owner:nil]) {
    NSLog(@"[osxclipboard] Access NSPasteboard failed");
    return;
}
if (![[NSPasteboard generalPasteboard] setString:text forType:NSPasteboardTypeString]) {
    NSLog(@"[osxclipboard] Set NSPasteboard string failed");
}

2. 清除剪切板内容：

[[NSPasteboard generalPasteboard] clearContents];

3. 监听剪切板内容变化：

NSPasteboard *pasteboard;
int i, changeCount = -1;
    
while (YES) {
    @autoreleasepool {
        pasteboard = [NSPasteboard generalPasteboard];
        // ignore init state
        if (changeCount == -1) {
            changeCount = (int)pasteboard.changeCount;
            continue;
        }
        if (changeCount == pasteboard.changeCount) {
            continue;
        }
        changeCount = (int)pasteboard.changeCount;
        
        // 读取改变的内容
        NSString *string = [pasteboard stringForType:NSPasteboardTypeString];
        if (!string.length) {
            continue;
        }
        
        NSLog(@"pasteboard: %@", string);
        sleep(CLIPBOARD_DETECT_INTERVAL);
}