{"id":4,"date":"2005-09-16T00:13:48","date_gmt":"2005-09-16T04:13:48","guid":{"rendered":"http:\/\/thesmithfam.org\/blog\/?p=4"},"modified":"2019-08-12T07:16:43","modified_gmt":"2019-08-12T13:16:43","slug":"qt-connecting-signals-to-signals","status":"publish","type":"post","link":"https:\/\/thesmithfam.org\/blog\/2005\/09\/16\/qt-connecting-signals-to-signals\/","title":{"rendered":"Qt: Connecting signals to … signals"},"content":{"rendered":"

I found out today that Qt’s slots\/signals architecture is even better than I thought. Normally, developers connect widget signals<\/b> to widget slots<\/b> to be notified of events. Today I discovered that signals can actually be connected to other signals, which saved me from writing some really stupid code…<\/p>\n

This may seem weird, but consider this scenario. You have a custom widget, called MyWidget<\/code>, that has a signal, somethingClicked()<\/code>, which is emitted when a user clicks, uh, something. But now you want to add a QPopupMenu<\/code> as a right-click context menu, that causes the somethingClicked()<\/code> signal to be emitted also. It turns out there’s a hard way and an easy way to do this.<\/p>\n

First, the hard way:<\/strong><\/p>\n

1. Add a new slot called emitSomethingClickedSlot()<\/code> that looks like this:<\/p>\n

\r\nMyWidget::emitSomethingClickedSlot() {\r\n        emit somethingClicked();\r\n}\r\n<\/pre>\n
2. Then, connect the QPopupMenu<\/code>‘s menu item to this slot, like so:<\/p>\n
\r\npopupMenu->insertItem( "Click me", this,\r\n     SLOT(emitSomethingClickedSlot()) );\r\n<\/pre>\n
That sucks. We just created a slot whose sole purpose is to turn around and emit a signal. What a waste of editor space. It would have been smarter to connect the menu item’s signal directly to the somethingClicked()<\/code> signal.<\/p>\n
Here’s the easy way:<\/strong><\/p>\n
\r\npopupMenu->insertItem( "Click me", this,\r\n     SIGNAL(somethingClicked()) );\r\n<\/pre>\n
Now that’s concise. Sometimes it pays to connect signals to signals.<\/p>\n","protected":false},"excerpt":{"rendered":"
Qt allows you to connect signals to slots, but did you know that you can connect signals to other signals? This makes it easier in some cases to move events around.<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-4","post","type-post","status-publish","format-standard","hentry","category-code-and-cruft"],"_links":{"self":[{"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/posts\/4","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/comments?post=4"}],"version-history":[{"count":2,"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/posts\/4\/revisions"}],"predecessor-version":[{"id":1629,"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/posts\/4\/revisions\/1629"}],"wp:attachment":[{"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/media?parent=4"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/categories?post=4"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/thesmithfam.org\/blog\/wp-json\/wp\/v2\/tags?post=4"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}