官方文档已经说得很详细了。
If you want to use other types as the key, make sure that you provide operator==() and a qHash() implementation.
Example:
#ifndef EMPLOYEE_H
#define EMPLOYEE_H
class Employee
{
public:
Employee() {}
Employee(const QString &name, const QDate &dateOfBirth);
...
private:
QString myName;
QDate myDateOfBirth;
};
inline bool operator==(const Employee &e1, const Employee &e2)
{
return e1.name() == e2.name()
&& e1.dateOfBirth() == e2.dateOfBirth();
}
inline uint qHash(const Employee &key, uint seed)
{
return qHash(key.name(), seed) ^ key.dateOfBirth().day();
}
#endif // EMPLOYEE_H
In the example above, we've relied on Qt's global qHash(const QString &, uint) to give us a hash value for the employee's name, and XOR'ed this with the day they were born to help produce unique hashes for people with the same name.
在此我直接总结下,方便查阅。
构造2个内联函数,方便QHash去对比一个是operator == ,一个是qHash(const QString &, uint);
这里要注意2点:
①operator==:这里要注意,判断2个自定义对象是否相等,如果有唯一标识字段,比如主键,就可以直接用那个,如果没有,就在结构体中想想,拿些字段组合可以唯一标识这个结构体;
②qHash(const QString &, uint):生成hash的,同样要传入唯一标识的,上面的例子是用name生成的hash再和出生时间异或。并且const QString &, uint这个函数是Qt的全局函数(从搬砖的角度看意思就是不需要去包QHash的头文件了)。
下面是己的例子,我这个结构体是对应数据库的,id是唯一标识:文章来源:https://www.toymoban.com/news/detail-511807.html
struct EncounterDB{
int id;
QString type; //F = dead
QString phase;
friend QDebug operator << (QDebug os, EncounterDB record){
os << "EncounterDB(" << record.id << "," << record.type << "," << record.phase << ")";
return os;
}
};
inline bool operator == (const AnswerDB &db1, const AnswerDB &db2){
return db1.id == db2.id;
}
inline uint qHash(const AnswerDB &db, uint seed){
return qHash(db.id, seed);
}
文章来源地址https://www.toymoban.com/news/detail-511807.html
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