Many applications that you will develop operate on input parameters set by the user. For example, it could be the color or position of some graphical elements or parameters used to set up communication with other applications. Reading configurations from external files is necessary for your applications. We will use a built-in Cinder support for reading and writing XML files to implement the configuration persistence mechanism.
Create two configurable variables in the main class: the IP address and the port of the host we are communicating with.
string mHostIP; int mHostPort;
Now we will implement the loadConfig and saveConfig methods and use them to load the configuration on application startup and save the changes while closing.
- Include the two following additional headers:
#include "cinder/Utilities.h" #include "cinder/Xml.h"
- We will prepare two methods for loading and saving the XML configuration file.
void MainApp::loadConfig() { try { XmlTree doc( loadFile( getAppPath() / fs::path("config.xml") ) ); XmlTree &generalNode = doc.getChild( "general" ); mHostIP = generalNode.getChild("hostIP").getValue(); mHostPort = generalNode.getChild("hostPort").getValue<int>(); } catch(Exception e) { console() << "ERROR: loading/reading configuration file." << endl; } } void MainApp::saveConfig() { std::string beginXmlStr( "<?xml version="1.0" encoding="UTF-8" ?>" ); XmlTree doc( beginXmlStr ); XmlTree generalNode; generalNode.setTag("general"); generalNode.push_back( XmlTree("hostIP", mHostIP) ); generalNode.push_back( XmlTree("hostPort", toString(mHostPort)) ); doc.push_back(generalNode); doc.write(writeFile( getAppPath() / fs::path("config.xml")) ); } - Now in the
setupmethod, inside our main class, we will put:// setup default values mHostIP = "127.0.0.1"; mHostPort = 1234; loadConfig();
- After this we will implement the
shutdownmethod as follows:void MainApp::shutdown() { saveConfig(); } - And don't forget to declare the
shutdownmethod in the main class:void shutdown();
The first two methods, loadConfig and saveConfig, are essential. The loadConfig method tries to open the config.xml file and find the general node. Inside the general node should be the hostIP and hostPort nodes. The values of these nodes will be assigned to corresponding variables in our application: mHostIP and mHostPort.
The
shutdown method is automatically triggered by Cinder just before the application closes, so our configuration values will be stored in the XML file when we quit the application. Finally, our configuration XML file looks like this:
<?xml version="1.0" encoding="UTF-8" ?> <general> <hostIP>127.0.0.1</hostIP> <hostPort>1234</hostPort> </general>
You can see clearly that the nodes are referring to application variables.