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<td >Qt 5.12</td><td ><a href="qtscript-index.html">Qt Script</a></td><td >Default Prototypes Example</td></tr></table><table class="buildversion"><tr>
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<h1 class="title">Default Prototypes Example</h1>
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<p>This Qt Script example shows how to use default prototypes to make a non-QObject-based type scriptable.</p>
<p class="centerAlign"><img src="images/defaultprototypes-example.png" alt="" /></p><p>With <a href="qscriptengine.html#setDefaultPrototype">QScriptEngine::setDefaultPrototype</a>() you can specify a Qt Script object that defines a scripting interface for a C++ type; Qt Script operations on values of such types will then be delegated to your prototype object. In this example, a simple scripting interface for QListWidgetItem is defined, so that the text of items can easily be accessed from script code.</p>
<p>To define a scripting API for QListWidgetItem in terms of Qt properties and slots, we subclass QObject and <a href="qscriptable.html">QScriptable</a>.</p>
<pre class="cpp">
<span class="keyword">class</span> ListWidgetItemPrototype : <span class="keyword">public</span> <span class="type">QObject</span><span class="operator">,</span> <span class="keyword">public</span> <span class="type"><a href="qscriptable.html">QScriptable</a></span>
{
Q_OBJECT
Q_PROPERTY(<span class="type">QString</span> text READ text WRITE setText)
<span class="keyword">public</span>:
ListWidgetItemPrototype(<span class="type">QObject</span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>);
<span class="type">QString</span> text() <span class="keyword">const</span>;
<span class="type">void</span> setText(<span class="keyword">const</span> <span class="type">QString</span> <span class="operator">&</span>text);
<span class="keyword">public</span> <span class="keyword">slots</span>:
<span class="type">QString</span> toString() <span class="keyword">const</span>;
};
</pre>
<p>A single property, <code>text</code>, is defined, along with a slot, <code>toString</code>.</p>
<pre class="cpp">
ListWidgetItemPrototype<span class="operator">::</span>ListWidgetItemPrototype(<span class="type">QObject</span> <span class="operator">*</span>parent)
: <span class="type">QObject</span>(parent)
{
}
<span class="type">QString</span> ListWidgetItemPrototype<span class="operator">::</span>text() <span class="keyword">const</span>
{
<span class="type">QListWidgetItem</span> <span class="operator">*</span>item <span class="operator">=</span> qscriptvalue_cast<span class="operator"><</span><span class="type">QListWidgetItem</span><span class="operator">*</span><span class="operator">></span>(thisObject());
<span class="keyword">if</span> (item)
<span class="keyword">return</span> item<span class="operator">-</span><span class="operator">></span>text();
<span class="keyword">return</span> <span class="type">QString</span>();
}
<span class="type">void</span> ListWidgetItemPrototype<span class="operator">::</span>setText(<span class="keyword">const</span> <span class="type">QString</span> <span class="operator">&</span>text)
{
<span class="type">QListWidgetItem</span> <span class="operator">*</span>item <span class="operator">=</span> qscriptvalue_cast<span class="operator"><</span><span class="type">QListWidgetItem</span><span class="operator">*</span><span class="operator">></span>(thisObject());
<span class="keyword">if</span> (item)
item<span class="operator">-</span><span class="operator">></span>setText(text);
}
<span class="type">QString</span> ListWidgetItemPrototype<span class="operator">::</span>toString() <span class="keyword">const</span>
{
<span class="keyword">return</span> <span class="type">QString</span>(<span class="string">"ListWidgetItem(text = %0)"</span>)<span class="operator">.</span>arg(text());
}
</pre>
<p>The implementation of the property accessors use the <a href="qscriptvalue.html#qscriptvalue_cast">qscriptvalue_cast</a>() function to cast the script object to a QListWidgetItem pointer. The normal C++ QListWidgetItem API is then used to implement the desired functionality.</p>
<p>Although not shown here, it is possible to throw a script exception from a prototype function; for example, you could throw a TypeError exception if the <a href="qscriptvalue.html#qscriptvalue_cast">qscriptvalue_cast</a>() fails.</p>
<p>QListWidgetItems are usually added to a QListWidget. While QListWidget is a QObject-based class, not all the functionality needed for this example are present. We can solve this by creating a default prototype for the QListWidget class as well. The prototype will augment the functionality already provided by the Qt Script QObject integration; i.e. if a property or slot is not found in the QListWidget object itself, the prototype will be used as a fallback.</p>
<pre class="cpp">
<span class="keyword">class</span> ListWidgetPrototype : <span class="keyword">public</span> <span class="type">QObject</span><span class="operator">,</span> <span class="keyword">public</span> <span class="type"><a href="qscriptable.html">QScriptable</a></span>
{
Q_OBJECT
<span class="keyword">public</span>:
ListWidgetPrototype(<span class="type">QObject</span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>);
<span class="keyword">public</span> <span class="keyword">slots</span>:
<span class="type">void</span> addItem(<span class="keyword">const</span> <span class="type">QString</span> <span class="operator">&</span>text);
<span class="type">void</span> addItems(<span class="keyword">const</span> <span class="type">QStringList</span> <span class="operator">&</span>texts);
<span class="type">void</span> setBackgroundColor(<span class="keyword">const</span> <span class="type">QString</span> <span class="operator">&</span>colorName);
};
</pre>
<p>The additional slots will make it possible to add items to a QListWidget from script code, and to set the background color of the widget from a string.</p>
<pre class="cpp">
ListWidgetPrototype<span class="operator">::</span>ListWidgetPrototype(<span class="type">QObject</span> <span class="operator">*</span>parent)
: <span class="type">QObject</span>(parent)
{
}
<span class="type">void</span> ListWidgetPrototype<span class="operator">::</span>addItem(<span class="keyword">const</span> <span class="type">QString</span> <span class="operator">&</span>text)
{
<span class="type">QListWidget</span> <span class="operator">*</span>widget <span class="operator">=</span> qscriptvalue_cast<span class="operator"><</span><span class="type">QListWidget</span><span class="operator">*</span><span class="operator">></span>(thisObject());
<span class="keyword">if</span> (widget)
widget<span class="operator">-</span><span class="operator">></span>addItem(text);
}
<span class="type">void</span> ListWidgetPrototype<span class="operator">::</span>addItems(<span class="keyword">const</span> <span class="type">QStringList</span> <span class="operator">&</span>texts)
{
<span class="type">QListWidget</span> <span class="operator">*</span>widget <span class="operator">=</span> qscriptvalue_cast<span class="operator"><</span><span class="type">QListWidget</span><span class="operator">*</span><span class="operator">></span>(thisObject());
<span class="keyword">if</span> (widget)
widget<span class="operator">-</span><span class="operator">></span>addItems(texts);
}
<span class="type">void</span> ListWidgetPrototype<span class="operator">::</span>setBackgroundColor(<span class="keyword">const</span> <span class="type">QString</span> <span class="operator">&</span>colorName)
{
<span class="type">QListWidget</span> <span class="operator">*</span>widget <span class="operator">=</span> qscriptvalue_cast<span class="operator"><</span><span class="type">QListWidget</span><span class="operator">*</span><span class="operator">></span>(thisObject());
<span class="keyword">if</span> (widget) {
<span class="preprocessor">#ifdef Q_WS_MAEMO_5</span>
<span class="type">QString</span> style <span class="operator">=</span> <span class="type">QString</span>(<span class="string">"QListWidget::item {background-color: %1;}"</span>)<span class="operator">.</span>arg(colorName);
style <span class="operator">+</span><span class="operator">=</span> <span class="string">"QListWidget::item {selection-color: black;}"</span>;
widget<span class="operator">-</span><span class="operator">></span>setStyleSheet(style);
<span class="preprocessor">#else</span>
<span class="type">QPalette</span> palette <span class="operator">=</span> widget<span class="operator">-</span><span class="operator">></span>palette();
<span class="type">QColor</span> color(colorName);
palette<span class="operator">.</span>setBrush(<span class="type">QPalette</span><span class="operator">::</span>Base<span class="operator">,</span> color);
widget<span class="operator">-</span><span class="operator">></span>setPalette(palette);
<span class="preprocessor">#endif</span>
}
}
</pre>
<p>Again, we use <a href="qscriptvalue.html#qscriptvalue_cast">qscriptvalue_cast</a>() to cast the script object to the relevant C++ type, in this case a QListWidget pointer. The addItem() and addItems() functions simply forward their arguments to the corresponding functions in the QListWidget class. setBackgroundColor() gets the widget's palette, creates a QColor from the given string argument and changes the palette accordingly.</p>
<pre class="cpp">
Q_DECLARE_METATYPE(<span class="type">QListWidgetItem</span><span class="operator">*</span>)
Q_DECLARE_METATYPE(<span class="type">QListWidget</span><span class="operator">*</span>)
</pre>
<p>The relevant C++ types must be made known to Qt's meta type system.</p>
<pre class="cpp">
<span class="type"><a href="qscriptengine.html">QScriptEngine</a></span> engine;
ListWidgetItemPrototype lwiProto;
engine<span class="operator">.</span>setDefaultPrototype(qMetaTypeId<span class="operator"><</span><span class="type">QListWidgetItem</span><span class="operator">*</span><span class="operator">></span>()<span class="operator">,</span>
engine<span class="operator">.</span>newQObject(<span class="operator">&</span>lwiProto));
ListWidgetPrototype lwProto;
engine<span class="operator">.</span>setDefaultPrototype(qMetaTypeId<span class="operator"><</span><span class="type">QListWidget</span><span class="operator">*</span><span class="operator">></span>()<span class="operator">,</span>
engine<span class="operator">.</span>newQObject(<span class="operator">&</span>lwProto));
</pre>
<p>For each type that we want to associate a prototype object with, we create an instance of the prototype class, pass it to <a href="qscriptengine.html#newQObject">QScriptEngine::newQObject</a>(), and then create the link between the C++ type and the resulting script object by calling <a href="qscriptengine.html#setDefaultPrototype">QScriptEngine::setDefaultPrototype</a>().</p>
<pre class="cpp">
<span class="type">QListWidget</span> listWidget;
engine<span class="operator">.</span>globalObject()<span class="operator">.</span>setProperty(<span class="string">"listWidget"</span><span class="operator">,</span>
engine<span class="operator">.</span>newQObject(<span class="operator">&</span>listWidget));
</pre>
<p>In this example, a single QListWidget object is added as a global script variable, called <code>listWidget</code>. Script code can add items to this widget by calling addItem() or addItems().</p>
<pre class="js">
listWidget.addItem("Red");
listWidget.addItem("Blue");
listWidget.addItem("Green");
listWidget.addItem("Cyan");
listWidget.addItem("Yellow");
listWidget.addItem("Purple");
listWidget.addItems(["Orange", "Gray"]);
</pre>
<p>Script code can connect to signals of the QListWidget object; signal handlers can use the interface defined in the QListWidgetItem prototype to manipulate item arguments.</p>
<pre class="js">
listWidget.currentItemChanged.connect(
function(item)
{
listWidget.setBackgroundColor(item.text);
}
);
</pre>
<p>Not shown in this example is how to make QListWidgetItem constructible from Qt Script code, i.e. to be able to write "new QListWidgetItem()" in a script. In order to do this, you have to define your own script constructor for the type. The constructor would just be a factory function that constructs a new C++ QListWidgetItem and returns it back to the script. See <a href="qscriptengine.html#newFunction">QScriptEngine::newFunction</a>() for more information.</p>
<p>Files:</p>
<ul>
<li><a href="qtscript-script-defaultprototypes-code-js.html">script/defaultprototypes/code.js</a></li>
<li><a href="qtscript-script-defaultprototypes-defaultprototypes-pro.html">script/defaultprototypes/defaultprototypes.pro</a></li>
<li><a href="qtscript-script-defaultprototypes-defaultprototypes-qrc.html">script/defaultprototypes/defaultprototypes.qrc</a></li>
<li><a href="qtscript-script-defaultprototypes-main-cpp.html">script/defaultprototypes/main.cpp</a></li>
<li><a href="qtscript-script-defaultprototypes-prototypes-cpp.html">script/defaultprototypes/prototypes.cpp</a></li>
<li><a href="qtscript-script-defaultprototypes-prototypes-h.html">script/defaultprototypes/prototypes.h</a></li>
</ul>
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