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qt:wiring_up_signals_and_slots

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qt:wiring_up_signals_and_slots [2011/04/03 13:07] – [Recommendation] mithatqt:wiring_up_signals_and_slots [2011/04/03 13:14] (current) – mithat
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 ===== Creating signal→slot connections ===== ===== Creating signal→slot connections =====
-Qt uses a [[signals and slots]] system to process events. If you use Qt Creator for development, there are at least four different ways to make signal->slot connections:+Qt uses a [[signals and slots]] system to process events. There are at least four different ways to make signal->slot connections:
   * [[#Create an "event handler"]]   * [[#Create an "event handler"]]
   * [[#Do it "visually"]]   * [[#Do it "visually"]]
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   * [[#Do it in the constructor ]]   * [[#Do it in the constructor ]]
  
-If you use Qt Designer with some other IDE for development, three of these are available to you. If you are hand-coding everything, then two are. Each of the above listed approaches are discussed below.+Each of the above listed approaches and when they are available are discussed below.
  
 ==== The alternatives ==== ==== The alternatives ====
  
 === Create an "event handler" === === Create an "event handler" ===
-//Availability: Qt Creator//+//Availability: Qt Creator and hand-coded projects (apparently)//
  
 Users of Visual Studio, Delphi, and Lazarus will be most familiar with this approach. In Qt Creator, right click on a control and select //Go to slot ...//. A dialog box giving you a list of signals available for the control will appear; select the signal for which you wish to create a handler. If the handler doesn't already exist, Qt Creator will create it and take you to it. If it does, then Qt Creator will just take you to it. Users of Visual Studio, Delphi, and Lazarus will be most familiar with this approach. In Qt Creator, right click on a control and select //Go to slot ...//. A dialog box giving you a list of signals available for the control will appear; select the signal for which you wish to create a handler. If the handler doesn't already exist, Qt Creator will create it and take you to it. If it does, then Qt Creator will just take you to it.
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 How does the build system know that that ''button_quit'''s ''clicked()'' signal connects to ''MainWindow'''s ''on_button_quit_event_clicked()'' slot? It appears that the connection between signals and slots created this way is done purely via a naming convention along the following lines: How does the build system know that that ''button_quit'''s ''clicked()'' signal connects to ''MainWindow'''s ''on_button_quit_event_clicked()'' slot? It appears that the connection between signals and slots created this way is done purely via a naming convention along the following lines:
 <code cpp-qt><widget-name> <signal-name>()</code> automatically connects to any slot of the form <code cpp-qt><ClassName>::on_<widget-name>_<signal-name>()</code> <code cpp-qt><widget-name> <signal-name>()</code> automatically connects to any slot of the form <code cpp-qt><ClassName>::on_<widget-name>_<signal-name>()</code>
-= Question =+ 
 +== Question ==
 If the above is true, then it should be possible to create event handlers just by writing code. Two tests are indicated: If the above is true, then it should be possible to create event handlers just by writing code. Two tests are indicated:
   * Write the handlers manually in Qt Creator.   * Write the handlers manually in Qt Creator.
   * Write the handlers manually in a project managed by something other than Qt Creator.   * Write the handlers manually in a project managed by something other than Qt Creator.
 +I've done both and assuming I didn't overlook something, indeed you can hand-add handlers as suggested.
  
 === Do it "visually" === === Do it "visually" ===
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 There are a couple special cases that are worth mentioning. There are a couple special cases that are worth mentioning.
  
-= Connecting to the window =+**Connecting to the window**
 If you want to connect a signal to the slot of a window, just drag onto the window rather than onto another widget. You will know you are connecting to the main window because the slot end of the connector will turn into an electrical earth ground symbol {{:qt:50px-earth_ground.svg.png?8|}} rather than an arrow. If you want to connect a signal to the slot of a window, just drag onto the window rather than onto another widget. You will know you are connecting to the main window because the slot end of the connector will turn into an electrical earth ground symbol {{:qt:50px-earth_ground.svg.png?8|}} rather than an arrow.
  
-= Connecting a widget to itself =+**Connecting a widget to itself**
 You can also connect widgets to themselves. If you do this, you can set up all sorts of hilarity. Sometimes you can even do useful things. You can also connect widgets to themselves. If you do this, you can set up all sorts of hilarity. Sometimes you can even do useful things.
  
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 ==== Recommendation ==== ==== Recommendation ====
-While the [[#Create an "event handler"]] approach is the fastest, I think using the Qt Designer approach of [[#Do it "visually"]] is actually the best way to do this--using the Signal/Slot editor panel if needed to add custom slots to the forms. The downside to this is that you have to hand-code the custom slots. The upsides are that the connections are well documented and that this approach simplifies moving your program from C++ to some other language (Python, Ruby, Java, etc.).+While the [[#Create an "event handler"]] approach is the fastest, my current thinking is that using the Qt Designer approach of [[#Do it "visually"]] is actually the best way to do this--using the Signal/Slot editor panel if needed to add custom slots to the forms. The downside to this is that you have to hand-code the custom slots. The upsides are that the connections are well documented and that this approach simplifies moving your program from C++ to some other language (Python, Ruby, Java, etc.).
  
 ===== Runtime signal→slot connection modifications ===== ===== Runtime signal→slot connection modifications =====
 I don't know. But it should be possible. I don't know. But it should be possible.
qt/wiring_up_signals_and_slots.1301836054.txt.gz · Last modified: 2011/04/03 13:07 by mithat
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