由于使用场景的不同，单例模式的写法也有所区别。

目前接触到的，大多数都是多线程，大量数据处理，还要考虑灵活性，对原有类结构改动最小等因素，所以写法更是多种多样。

QT个人较常用的一种写法：（两个文件：分为.h文件和.cpp文件）

1 class LocalBusiness : public QObject
2 {
3 Q_OBJECT
4
5 private:
6 QString _myName;
7 explicit LocalBusiness(QObject *parent = nullptr);
8 static LocalBusiness* _instance;
9 public:
10 static LocalBusiness* Instance()
11 {
12 static QMutex mutex;
13 if (!_instance) {
14 QMutexLocker locker(&mutex);
15 if (!_instance) {
16 _instance = new LocalBusiness;
17 }
18 }
19 return _instance;
20 }
21 public:
22 void SayHello();
23
24 };

1 LocalBusiness* LocalBusiness::_instance = nullptr;
2
3 LocalBusiness::LocalBusiness(QObject *parent) : QObject(parent)
4 {
5 _myName="LocalBusiness";
6 }
7
8 void LocalBusiness::SayHello()
9 {
10 qDebug() << "hello,"+_myName;
11 }

具体调用

1 LocalBusiness::Instance()->SayHello();

C#个人较常用的写法：（一个文件：.cs文件）

1 public class LocalBusiness
2 {
3 private readonly string _myName = string.Empty;
4 private static LocalBusiness _instance = null;
5 private static readonly object _locker = new object();
6
7 private LocalBusiness()
8 {
9 _myName = "LocalBusiness";
10 }
11
12 public static LocalBusiness Instance
13 {
14 get
15 {
16 if (_instance == null)
17 {
18 lock (_locker)
19 {
20 if (_instance == null)
21 {
22 _instance = new LocalBusiness();
23 }
24 }
25 }
26 return _instance;
27 }
28 }
29
30 public void SayHello()
31 {
32 Console.WriteLine("hello,"+ _myName);
33 }
34 }

具体调用

1 LocalBusiness.Instance.SayHello();

如果有帮助，欢迎素质三连~