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<div class='klayout-generated-doc'><p class="navigator"><b>KLayout Documentation (Qt 5): </b><a href="../index.html">Main Index</a> » <a href="index.html">Programming scripts</a> » Events And Callbacks</p><h1>Events And Callbacks</h1><a name="k_1"></a><a name="k_2"></a><ul><li><a href="#h2-12">Introduction</a></li><li><a href="#h2-51">Reimplementation (Strategy Pattern)</a></li><li><a href="#h2-126">Events</a></li></ul><a name="h2-12"></a><h2>Introduction</h2><p> |
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In some places, the API requires to attach code to an event. An event could be a menu item which is selected |
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or a change of some status which might require some action. The API allows implementation of specific code which is |
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called in that case. This enables us to implement the functionality |
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behind a menu item. In this text we will refer to such functionality by the general term "callback". In general |
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a callback is custom code that is called from the API in contrast to API code that is called from the custom code. |
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</p><p> |
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There are basically two ways to attach specific code to a callback: |
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</p><ul><li><b>Reimplementation</b>: some API classes provide "virtual" methods. "virtual" is a C++ term and |
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means a method that can be overridden in a derived class. This technique is employed for example in the |
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"Strategy" design pattern. In strictly typed C++ this is quite a common pattern which allows definition of interfaces |
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and concrete implementations based on those interfaces. Ruby as a dynamic language doesn't care much about |
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classes and their relationship: an object either has a method or it hasn't. So, reimplementation is just a matter |
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of providing the right method. An examples for the strategy pattern is the BrowserSource class (<a href="../code/class_BrowserSource.html">BrowserSource</a>). |
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</li><li><b>Events</b>: events allow attaching a piece of code to an event. In Ruby, such a block is "Proc" object, in "Python" it is a |
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"callable" object ("lambda function" is a term used in both languages for this kind of concept). |
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In case the event is triggered, this attached code is executed. Multiple lambda functions can be attached to the same event and |
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removed from the latter. Events can be cleared of attached code, where only the blocks attached from one language can be cleared |
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together - code attached from Python cannot be cleared from Ruby. |
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An example for events is the Action class (<a href="../code/class_Action.html">Action</a>) which provides both the reimplementation interface |
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("triggered" method) and the event interface ("on_triggered"). By the way, Qt signals are mapped to events in KLayout's Qt |
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binding (<a href="qt_binding.html">The Qt Binding</a>). |
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</li></ul><p> |
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The "Observer" class which was there prior to KLayout 0.25 has been dropped in favour of the more |
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flexible events. It is no longer supported. |
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</p><a name="h2-51"></a><h2>Reimplementation (Strategy Pattern)</h2><p> |
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The BrowserSource (<a href="../code/class_BrowserSource.html">BrowserSource</a>) class is a nice example for the Strategy pattern. |
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It is used by the BrowserDialog class (<a href="../code/class_BrowserDialog.html">BrowserDialog</a>) as a kind of internal HTML server |
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which handles URL's starting with "int:". For this, a script has to provide a class that reimplements the "get(url)" |
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method. In the following example, a BrowserSource is created that takes an URL with an integer index number and |
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delivers a HTML text with a link to the URL with the next index. |
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</p><p> |
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Here is the code. |
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This example demonstrates how the "get" method is reimplemented to deliver the actual text. |
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</p><pre> |
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module MyMacro |
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include RBA |
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class MyBrowserSource < BrowserSource |
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def get(url) |
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next_url = url.sub(/\d+/) { |num| (num.to_i+1).to_s } |
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"This is #{url}. <a href='#{next_url}'>Goto next (#{next_url})</a>" |
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end |
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end |
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dialog = BrowserDialog::new |
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dialog.source = MyBrowserSource::new |
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dialog.home = "int:0" |
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dialog.exec |
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end |
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</pre> |
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The Python version is this: |
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<pre> |
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from pya import BrowserSource, BrowserDialog |
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class MyBrowserSource(BrowserSource): |
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def get(self, url): |
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next_url = "int:" + str(int(url.split(":")[1]) + 1) |
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return f"This is {url}. <a href='{next_url}'>Goto next ({next_url})</a>>" |
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dialog = BrowserDialog() |
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dialog.home = "int:0" |
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dialog.source = MyBrowserSource() |
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dialog.exec_() |
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</pre><p> |
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Ruby even allows reimplementation of a method without deriving a new class, because it allows |
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defining methods per instance: |
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</p><pre> |
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module MyMacro |
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include RBA |
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source = BrowserSource::new |
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def source.get(url) |
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next_url = url.sub(/\d+/) { |num| (num.to_i+1).to_s } |
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"This is #{url}. <a href='#{next_url}'>Goto next (#{next_url})</a>" |
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end |
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dialog = BrowserDialog::new |
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dialog.source = source |
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dialog.home = "int:0" |
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dialog.exec |
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end |
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</pre><a name="h2-126"></a><h2>Events</h2><p> |
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Events are the callback variant which is the easiest one to use. Using an event it is possible |
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to directly attach a block of code to a callback. An event has a specific signature, i.e. |
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the parameters it provides. The block can obtain this parameters by listing them in its argument list. |
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</p><p> |
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Here is a simple example that uses the parameterless "on_triggered" event of the Action |
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class (<a href="../code/class_Action.html">Action</a>). It puts a new entry into the tool bar and if it is |
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clicked, it displays a message box: |
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</p><pre> |
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module MyMacro |
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include RBA |
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action = Action::new |
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action.on_triggered do |
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MessageBox::info("A message", "The action was triggered", MessageBox::Ok) |
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end |
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action.title = "My Action" |
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Application::instance.main_window.menu.insert_item("@toolbar.end", "my_action", action) |
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end |
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</pre><p> |
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The Python version is: |
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</p><pre> |
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from pya import Action, MessageBox, Application |
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def on_triggered(): |
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MessageBox.info("A message", "The action was triggered", MessageBox.Ok) |
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action = Action() |
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action.on_triggered = on_triggered |
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action.title = "My Action" |
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Application.instance().main_window().menu().insert_item("@toolbar.end", "my_action", action) |
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</pre><p> |
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Specifying a block to an event will make the event only execute that block. A more flexible way of |
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controlling the code attached to events is available through the += and -= operators: |
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</p><pre> |
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module MyMacro |
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include RBA |
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code = lambda do |
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MessageBox::info("A message", "The action was triggered", MessageBox::Ok) |
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end |
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action = Action::new |
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action.on_triggered += code |
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... |
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# to remove the code from the event, use: |
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action.on_triggered -= code |
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# to replace all event handlers by the one given by "code": |
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action.on_triggered = code |
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# to clear all event handlers use: |
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action.on_triggered.clear |
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</pre><p> |
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Synonyms for the <tt>+=</tt> operator are <tt>add</tt> and <tt>connect</tt>. The latter makes code more familiar for PyQt users. |
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In the same way, synonyms for the <tt>-=</tt> operator are <tt>remove</tt> and <tt>disconnect</tt>. |
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</p><p> |
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If the Qt binding is available (see <a href="qt_binding.html">The Qt Binding</a>), Qt signals |
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are implemented as events. This way it's very simple to create a Qt dialog. In following example, |
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|
the "textChanged" signal of QLineEdit is attached a code block which copies the text of the |
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input field to the label below: |
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</p><pre> |
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module MyMacro |
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include RBA |
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dialog = QDialog::new(Application::instance.main_window) |
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layout = QVBoxLayout::new(dialog) |
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input = QLineEdit::new(dialog) |
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label = QLabel::new(dialog) |
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layout.addWidget(input) |
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layout.addWidget(label) |
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# implement the textChanged signal as event: |
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input.textChanged { |text| label.text = text } |
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dialog.exec |
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end |
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</pre><p> |
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The Python version is: |
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</p><pre> |
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from pya import QDialog, QVBoxLayout, QLineEdit, QLabel, Application |
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|
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|
dialog = QDialog(Application.instance().main_window()) |
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layout = QVBoxLayout(dialog) |
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|
input = QLineEdit(dialog) |
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label = QLabel(dialog) |
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layout.addWidget(input) |
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layout.addWidget(label) |
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def text_changed(text): |
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label.text = text |
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# implement the textChanged signal as event: |
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input.textChanged = text_changed |
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dialog.exec_() |
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</pre><p> |
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Using the += operator on the event, multiple handlers can be added to a signal: |
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</p><pre> |
|
|
module MyMacro |
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|
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include RBA |
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|
|
dialog = QDialog::new(Application::instance.main_window) |
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layout = QVBoxLayout::new(dialog) |
|
|
input = QLineEdit::new(dialog) |
|
|
label1 = QLabel::new(dialog) |
|
|
label2 = QLabel::new(dialog) |
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|
layout.addWidget(input) |
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layout.addWidget(label1) |
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|
layout.addWidget(label2) |
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|
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|
# two signal consumers: |
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|
input.textChanged += lambda { |text| label1.text = text } |
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|
input.textChanged += lambda { |text| label2.text = text.reverse } |
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dialog.exec |
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|
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end |
|
|
</pre><p> |
|
|
with the Python version: |
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|
</p><pre> |
|
|
from pya import QDialog, QVBoxLayout, QLineEdit, QLabel, Application |
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|
|
|
dialog = QDialog(Application.instance().main_window()) |
|
|
layout = QVBoxLayout(dialog) |
|
|
input = QLineEdit(dialog) |
|
|
label1 = QLabel(dialog) |
|
|
label2 = QLabel(dialog) |
|
|
layout.addWidget(input) |
|
|
layout.addWidget(label1) |
|
|
layout.addWidget(label2) |
|
|
|
|
|
def text_changed1(text): |
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|
label1.text = text |
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|
|
|
|
def text_changed2(text): |
|
|
label2.text = text[::-1] |
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|
|
|
# two signal consumers: |
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|
input.textChanged += text_changed1 |
|
|
input.textChanged += text_changed2 |
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|
|
|
|
dialog.exec_() |
|
|
</pre></div> |
|
|
</div> |
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|
</body> |
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</html> |
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