Rep lica C ompiler (repc) generates QObject header files based on an API definition file. The file (called a "rep" file) uses a specific (text) syntax to describe the API. By convention, these files are given a .rep file extension, short for Replica. When these files are processed by repc, repc generates both 源 and 复本 头文件。
The Qt Remote Objects module also includes CMake 函数 and qmake 变量 that can be added to your project file to automatically run repc, and add the resulting files to the list of files processed by 元对象编译器 during the build process, making use of Qt Remote Objects in your projects simple.
While Qt Remote Objects supports sharing any QObject over the network (using enableRemoting on the Source side and acquireDynamic on the Replica side), there are a couple of advantages to letting repc define your objects. First of all, while DynamicReplicas are useful, they are more cumbersome to work with. The API is not known until the object is initialized, and using the API from C++ requires string lookups through QMetaObject 's methods. Secondly, having the interface known at compile time finds any issues at compile vs. at runtime. Thirdly, the rep format supports default values, which can be handy if you are unable to ensure the Source is available when the Replica is instantiated.
见文档编制 here for information on using the generated files in your code. Here we will focus on the repc format and options.
rep 文件格式是简单 DSL (领域特定语言) 用于描述 QtRO (Qt 远程对象) 支持接口。由于 QtRO 是基于系统的对象，所以这些接口由透过对象 (也就是说，具有特性、信号及槽的类) 获得的 API 定义。
Each class defined in a rep file becomes a QObject in the generated header files, with the described API generated for you.
要定义类，使用
class
keyword, followed by the name you want for your type, and then enclose your API in brackets like so
class MyType { //PROP/CLASS/MODEL/SIGNAL/SLOT/ENUM declarations to define your API };
Q_PROPERTY
elements are created by using the PROP keyword in the rep file. The syntax is the
PROP
keyword followed by the definition enclosed in parentheses, where the definition is the type, the name, and (optionally) a default value or attributes.
PROP(bool simpleBool) // boolean named simpleBool PROP(bool defaultFalseBool=false) // boolean named defaultFalseBool, with false // as the default value PROP(int lifeUniverseEverything=42) // int value that defaults to 42 PROP(QByteArray myBinaryInfo) // Qt types are fine, may need #include // additional headers in your rep file PROP(QString name CONSTANT) // Property with the CONSTANT attribute PROP(QString setable READWRITE) // Property with the READWRITE attribute // note: Properties default to READPUSH // (see description below) PROP(SomeOtherType myCustomType) // Custom types work. Needs #include for the // appropriate header for your type, make // sure your type is known to the metabject // system, and make sure it supports Queued // Connections (see Q_DECLARE_METATYPE and // qRegisterMetaType)
有关创建自定义类型的更多信息，可以找到 here .
By default, properties will have getters and a "push" slot defined, as well as a notify signal emitted when the value is changed. Qt Remote Objects requires the notify signal on the Source object to trigger sending updates to the attached Replicas. In earlier versions of QtRO, properties defaulted to being read/write, that is, having getters and setters. However, due to the asynchronous nature of QtRO, this led to unintuitive behavior at times. Setting the READWRITE attribute on the PROP will provide the old (getter and setter) behavior.
// In .rep file, old (setter) behavior PROP(int myVal READWRITE) // Old behavior with setMyVal(int myVal) method // In code... Assume myVal is initially set to 0 in Source int originalValue = rep->myVal(); // Will be 0 rep->setMyVal(10); // Call setter, expecting a blocking/ // non-asynchronous return if (rep->myVal() == 10) ... // Test will usually fail
If it is necessary to block until the value is changed, something like the following is necessary.
// In .rep file, old (setter) behavior PROP(int myVal READWRITE) // Old behavior with setMyVal(int myVal) method // In code... Assume myVal is initially set to 0 in Source bool originalValue = rep->myVal(); // Will be 0 // We can wait for the change using \l QSignalSpy QSignalSpy spy(rep, SIGNAL(myValChanged(int))); rep->setMyVal(10); // Call setter, expecting a blocking/ // non-asynchronous return spy.wait(); // spy.wait() blocks until changed signal // is received if (rep->myVal() == 10) ... // Test will succeed assuming // 1. Source object is connected // 2. Nobody else (Source or other Replica) // sets the myVal to something else (race // condition) // Rather than use QSignalSpy, the event-driven practice would be to connect the // myValChanged notify signal to a slot that responds to the changes.
QtRO now defaults to READPUSH, which provides an automatically generated slot for requesting a property change.
// In .rep file, defaults to READPUSH PROP(bool myVal) // No setMyVal(int myVal) on Replica, has // pushMyVal(int myVal) instead // In code... Assume myVal is initially set to 0 in Source bool originalValue = rep->myVal(); // Will be 0 // We can wait for the change using \l QSignalSpy QSignalSpy spy(rep, SIGNAL(myValChanged(int))); rep->pushMyVal(10); // Call push method, no expectation that change // is applied upon method completion. // Some way of waiting for change to be received by the Replica is still necessary, // but hopefully not a surprise with the new pushMyVal() Slot. spy.wait(); // spy.wait() blocks until changed signal // is received if (rep->myVal() == 10) ... // Test will succeed assuming // 1. Source object is connected // 2. Nobody else (Source or other Replica) // set the myVal to something else (race // condition)
还可以使用
CONSTANT
,
READONLY
,
PERSISTED
,
READWRITE
,
READPUSH
，或
SOURCEONLYSETTER
keywords in the PROP declaration, which affects how the property is implemented. READPUSH is the default value if no value used.
PROP(int lifeUniverseEverything=42 CONSTANT) PROP(QString name READONLY)
Please note there are some subtleties here. A CONSTANT PROP has a Q_PROPERTY declared as CONSTANT on the SOURCE side. However, replicas cannot know the correct value until they are initialized, which means the property value has to be allowed to change during initialization. For READONLY, the source will have neither a setter nor a push slot, and the replica side will not have a push slot generated. Adding the PERSISTED trait to a PROP will have the PROP use the QRemoteObjectAbstractPersistedStore instance set on a Node (if any) to save/restore PROP values.
Another nuanced value is SOURCEONLYSETTER, which provides another way of specifying asymmetric behavior, where the
源
(具体帮手类
SimpleSource
) will have a public getter and setter for the property, but it will be ReadOnly (with a notify signal) on the
复本
side. Thus the property can be fully controlled from the
源
side, but only observed from the
复本
side. SOURCEONLYSETTER is the mode used by repc for MODEL and CLASS instances, meaning the
源
can change the pointed to object, but the
复本
can not provide a new object, as no set<Prop> or push<Prop> method is generated. Note, this does not impact the behavior of the pointed to type's properties, just the ability to change the pointer itself.
CLASS 关键词生成特殊
Q_PROPERTY
元素对于对象派生自
QObject
. These properties have the same semantics as SOURCEONLYSETTER. The syntax is the
CLASS
keyword followed by the property name and then the type of subobject enclosed in parentheses.
// In .rep file class OtherClass { PROP(int value) } class MainClass { CLASS subObject(OtherClass) }
MODEL 关键词生成特殊
Q_PROPERTY
元素对于对象派生自
QAbstractItemModel
. These properties have the same semantics as SOURCEONLYSETTER. The syntax is the
MODEL
keyword followed by the property name and then parentheses enclosing the (comma-separated) roles that should be exposed to the replica.
// In .rep file class CdClass { PROP(QString title READONLY) MODEL tracks(title, artist, length) }
信号 methods are created by using the SIGNAL keyword in the rep file.
用法是声明
SIGNAL
followed by the desired signature wrapped in parentheses. The void return value should be skipped.
SIGNAL(test()) SIGNAL(test(QString foo, int bar)) SIGNAL(test(QMap<QString,int> foo)) SIGNAL(test(const QString &foo)) SIGNAL(test(QString &foo))
就像在 Qt 队列连接 , parameters in signals that are references will be copied when being passed to replicas.
槽 methods are created by using the SLOT keyword in the rep file.
用法是声明
SLOT
followed by the desired signature wrapped in parentheses. The return value can be included in the declaration. If the return value is skipped, void will be used in the generated files.
SLOT(test()) SLOT(void test(QString foo, int bar)) SLOT(test(QMap<QString,int> foo)) SLOT(test(QMap<QString,int> foo, QMap<QString,int> bar)) SLOT(test(QMap<QList<QString>,int> foo)) SLOT(test(const QString &foo)) SLOT(test(QString &foo)) SLOT(test(const QMap<QList<QString>,int> &foo)) SLOT(test(const QString &foo, int bar))
就像在 Qt 队列连接 and QtRO SIGNALS, parameters in slots that are references will be copied when being passed to Replicas.
Enumerations (which use a combination of C++ enum and Qt's Q_ENUM in QtRO) are described using the ENUM keyword.
ENUM MyEnum {Foo}
ENUM MyEnum {Foo, Bar}
ENUM MyEnum {Foo, Bar = -1}
ENUM MyEnum {Foo=-1, Bar}
ENUM MyEnum {Foo=0xf, Bar}
ENUM MyEnum {Foo=1, Bar=3, Bas=5}
相关话题： ENUM 类型 , USE_ENUM 关键词
Plain Old Data (POD) is a term to describe a simple data collection, along the lines of a C++ struct. For example, if you have an API for a phonebook, you may want to use the concept of an "address" in its interface (where address might include street, city, state, country, and postal code). You can use the POD keyword to define objects like this, which can then be used by in PROP/SIGNAL/SLOT definitions in your class definitions.
用法是声明
POD
followed by the name for the generated type, followed by type and name pairs separated by commas, where the type/name pairs are wrapped in parentheses.
POD Foo(int bar) POD Foo(int bar, double bas) POD Foo(QMap<QString,int> bar) POD Foo(QList<QString> bar) POD Foo(QMap<QString,int> bar, QMap<double,int> bas)
完整范例看起来像这样
POD Foo(QList<QString> bar) class MyType { SIGNAL(sendCustom(Foo foo)); };
The code generated by repc creates a Q_GADGET class for each POD, with corresponding Q_PROPERTY members for each type defined for the POD.
It is often easier and cleaner to define an ENUM inside a class (see
ENUM
), but if you need a standalone enum type, using the ENUM keyword outside of a class definition can be helpful. This will generate a new class in your header files that handles marshalling, etc.. The syntax is identical to
ENUM
, with the exception that the declaration in this case is not contained in a
class
声明。
相关话题： ENUM , USE_ENUM 关键词
The USE_ENUM keyword was implemented before autogeneration via the ENUM keyword was added. It is kept for backwards compatibility.
The rep file defines an interface, but interfaces often require external elements. In order to support this, repc will include any (single line) directives at the top of the generated files. This allows you to, for instance, use #include or #define directives that support the logic or datatypes needed.
The repc tool currently ignores everything from the "#" symbol to the end-of-line and adds that to the generated files. So multi-line #if/#else/#endif statements and multi-line macros are not supported.
The CMake functions for generating source and replica types are listed below.
| qt_add_repc_merged | Creates C++ header files for source and replica types from the Qt Remote Objects .rep files. |
| qt_add_repc_replicas | Creates C++ header files for replica types from the Qt Remote Objects .rep files. |
| qt_add_repc_sources | Creates C++ header files for source types from the Qt Remote Objects .rep files. |
| qt_reps_from_headers | Creates .rep files from the QObject header files. |
Specifies the names of all rep files in the project that should be used to generate replica header files.
例如：
REPC_REPLICA = media.rep \ location.rep
The generated file(s) will be of the form
rep_<replica file base>_replica.h
.
Specifies the names of all rep files in the project that should be used to generate source header files.
例如：
REPC_SOURCE = media.rep \ location.rep
The generated file(s) will be of the form
rep_<replica file base>_source.h
.
Specifies the names of all rep files in the project that should be used to generate combined (source and replica) header files.
例如：
REPC_MERGED = media.rep \ location.rep
The generated file(s) will be of the form
rep_<replica file base>_merged.h
.
注意： Typically sources and replicas live in separate processes or devices, so this variable is not commonly used.
指定名称为现有 QObject header files that should be used to generate corresponding .rep files.