GUI界面
限制输入的内容
1QValidator *validator = new QIntValidator(100, 999, this);
2// 这样文本框只能输入100~999之间的数字
3ui->lineEdit->setValidator(validator);
显示格式控制
1ui->textEdit->setWordWrapMode(QTextOption::WrapAnywhere); // 任意地方换行
2ui->tableWidget->setTextElideMode(Qt::ElideMode); // 不显示省略号
Qt序列化
通过全局流操作运算符重载实现，可以序列化到文件等设备中，也可以序列化到QByteArray中。
1// cmdinfo.h
2// BaseInfo已经实现序列化
3class CmdInfo : public BaseInfo {
4public:
5 friend QDataStream& operator>>(QDataStream&, CmdInfo&);
6 friend QDataStream& operator<<(QDataStream&, const CmdInfo&);
7
8private:
9 QString command_;
10 CmdType type_;
11};
12
13// cmdinfo.cpp
14QDataStream& operator>>(QDataStream &in, CmdInfo &data)
15{
16 BaseInfo &base = data;
17 qint32 tmpInt;
18
19 in >> base >> data.command_ >> tmpInt;
20 data.setType((CmdType)tmpInt);
21 return in;
22}
23QDataStream& operator<<(QDataStream &out, const CmdInfo &data)
24{
25 const BaseInfo &base = data;
26 out << base << data.command_ << (qint32)data.type_;
27 return out;
28}
序列化到文件中
1// 读
2QFile file("object.dat");
3file.open(QFile::ReadOnly);
4QDataStream in(&file);
5in >> infoObj;
6file.close();
7
8// 写
9QFile file(datFilename(filename));
10file.open(QFile::Truncate | QFile::WriteOnly);
11QDataStream out(&file);
12out << infoObj;
13file.flush();
14file.close();
序列化到QByteArray中
1// The QBuffer class provides a QIODevice interface for a QByteArray.
2QByteArray byteArray;
3QBuffer buffer(&byteArray);
4buffer.open(QIODevice::WriteOnly);
5
6QDataStream out(&buffer);
7out << QApplication::palette();
QDateTime也重载了关于QDateTime和QDebug的全局流操作符
1class QDateTime {
2 friend Q_CORE_EXPORT QDataStream &operator<<(QDataStream &, const QDateTime &);
3 friend Q_CORE_EXPORT QDataStream &operator>>(QDataStream &, QDateTime &);
4
5 friend Q_CORE_EXPORT QDebug operator<<(QDebug, const QDateTime &);
6};
QByteArray的Copy-On-Write
QByteArray can be used to store both raw bytes (including ‘\0’s) and traditional 8-bit ‘\0’-terminated strings. Using QByteArray is much more convenient than using
const char *. Behind the scenes, it always ensures that the data is followed by a ‘\0’ terminator, and uses implicit sharing (copy-on-write) to reduce memory usage and avoid needless copying of data.
1#include <QByteArray>
2#include <QDebug>
3
4int main()
5{
6 char buf[] = {'1', '2', 0, '3'};
7 QByteArray ba1 = QByteArray::fromRawData(buf, 4);
8 QByteArray ba2 = QByteArray(buf, 4); // 深拷贝
9 qDebug() << ba2.size(); // 4
10 // buf的地址和ba1.constData()的地址相同
11 printf("buf=%p, ba1=%p, ba2=%p\n", buf, ba1.constData(), ba2.constData());
12
13 // 注意: data()接口会触发深拷贝，而constData不会触发深拷贝
14 ba1.data();
15 printf("buf=%p, ba1=%p, ba2=%p\n", buf, ba1.constData(), ba2.constData());
16 return 0;
17}
18
19// 输出：
20// 4
21// buf=0067fea4, ba1=0067fea4, ba2=012475d8
22// buf=0067fea4, ba1=0124b6f8, ba2=012475d8
底层原理
1// qbytearray.h
2
3inline char *QByteArray::data()
4{ detach(); return d->data(); }
5
6inline const char *QByteArray::data() const
7{ return d->data(); }
8
9inline const char *QByteArray::constData() const
10{ return d->data(); }
11
12inline void QByteArray::detach()
13{ if (d->ref.isShared() || (d->offset != sizeof(QByteArrayData))) reallocData(uint(d->size) + 1u, d->detachFlags()); }