[英]How to Use Models with QML?
I have a GUI written in qml and c++. 我有一个用qml和c ++编写的GUI。 There are 2 comboboxes (qt control 5.1).
有2个组合框(qt控件5.1)。 Second combobox has to update at runtime whenever the value of the first one is changed.
每当第一个组合框的值更改时,第二个组合框就必须在运行时进行更新。
maincontext->setContextProperty("typemodel", QVariant::fromValue(m_typemodel));
maincontext->setContextProperty("unitmodel", QVariant::fromValue(m_unitmodel));
These are 2 models that I give to qml from c++. 这些是我从c ++给qml的2个模型。
ComboBox {
id: typebox
anchors.left: text1.right
anchors.leftMargin: 5
signal changed(string newtext)
width: 70
height: 23
anchors.top: parent.top
anchors.topMargin: 37
model: typemodel
onCurrentTextChanged: {
mainwin.unitGenerator(typebox.currentText);
}
This is the first combobox. 这是第一个组合框。 As you see, the c++ model of second combobox is updated every time the value of the first is changed (mainwin.unitGenerator(typebox.currentText)).
如您所见,第二个组合框的c ++模型在每次更改第一个组合框的值时都会更新(mainwin.unitGenerator(typebox.currentText))。 But it does not seem to update the combobox's model.
但是它似乎并没有更新组合框的模型。
How can I update qml's model on runtime? 如何在运行时更新qml的模型?
To even begin to address your issue, we'd need to see what the unitGenerator
method does. 为了甚至可以解决您的问题,我们需要查看
unitGenerator
方法的作用。 If you're using a custom model, it's almost certain that you're not correctly implementing the notifications. 如果您使用的是自定义模型,则几乎可以肯定您没有正确实现通知。 My bet at the moment would be that you're not signaling the model reset.
目前,我的赌注是您未表示要重置模型。
Below is a complete code example that shows how you can tie a QStringListModel
to an editable ListView
and to ComboBox
es. 下面是一个完整的代码示例,该示例显示如何将
QStringListModel
绑定到可编辑的ListView
和ComboBox
。 The second ComboBox
's model is regenerated based on the selection from the first one. 根据第一个
ComboBox
的选择,重新生成第二个ComboBox
的模型。 This presumably approximates your desired functionality. 据推测这近似于您所需的功能。
Note the specific handling of roles done by the QStringListModel
. 注意
QStringListModel
完成的角色处理。 The model treats the display and edit roles almost the same: they both are mapped to the string value in the list. 该模型对待显示和编辑角色几乎相同:它们都映射到列表中的字符串值。 Yet when you update a particular role's data, the
dataChanged
signal carries only the role that you've changed. 但是,当您更新特定角色的数据时,
dataChanged
信号仅携带您已更改的角色。 This can be used to break a binding loop that might be otherwise present in the model editor item (TextInput). 这可用于打破模型编辑器项(TextInput)中可能存在的绑定循环。 When you use a custom model, you may need to implement similar functionality.
使用自定义模型时,可能需要实现类似的功能。
The display
role is used to bind the combo boxes to the model. display
角色用于将组合框绑定到模型。 The edit
role is used to pre-populate the editor objects. edit
角色用于预填充编辑器对象。 The editor's onTextChanged
signal handler is updating the display
role, and this doesn't cause a binding loop to itself. 编辑器的
onTextChanged
信号处理程序正在更新display
角色,并且这不会导致自身的绑定循环。 If the handler was updating the edit
role, it would cause a binding loop via the text
property. 如果处理程序正在更新
edit
角色,则将通过text
属性引起绑定循环。
There are various kinds of "models" in QML. QML中有各种各样的“模型”。 Internally, QML will wrap almost "anything" in a model.
在内部,QML会将模型中的几乎“任何内容”包装起来。 Anything that is internally not a QObject yet can still be a model (say a
QVariant
), won't be notifying anyone about anything. 内部上不是QObject的任何事物仍然可以是模型(例如
QVariant
),不会将任何事情通知任何人。
For example, a "model" based on QVariant
that wraps an int
will not issue notifications, because QVariant
is not a QObject
that could signal changes. 例如,基于
QVariant
包装了int
的“模型”将不会发出通知,因为QVariant
不是可以表示更改的QObject
。
Similarly, if your "model" is tied to a property value of a class derived from QObject
, but you fail to emit
the property change notification signal, it also won't work. 同样,如果您的“模型”与从
QObject
派生的类的属性值绑定在一起,但是您未能emit
属性更改通知信号,那么它也将不起作用。
Without knowing what your model types are, it's impossible to tell. 如果不知道您的模型类型是什么,就无法分辨。
main.qml main.qml
import QtQuick 2.0
import QtQuick.Controls 1.0
ApplicationWindow {
width: 300; height: 300
ListView {
id: view
width: parent.width
anchors.top: parent.top
anchors.bottom: column.top
model: model1
spacing: 2
delegate: Component {
Rectangle {
width: view.width
implicitHeight: edit.implicitHeight + 10
color: "transparent"
border.color: "red"
border.width: 2
radius: 5
TextInput {
id: edit
anchors.margins: 1.5 * parent.border.width
anchors.fill: parent
text: edit // "edit" role of the model, to break the binding loop
onTextChanged: model.display = text
}
}
}
}
Column {
id: column;
anchors.bottom: parent.bottom
Text { text: "Type"; }
ComboBox {
id: box1
model: model1
textRole: "display"
onCurrentTextChanged: generator.generate(currentText)
}
Text { text: "Unit"; }
ComboBox {
id: box2
model: model2
textRole: "display"
}
}
}
main.cpp main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickWindow>
#include <QStringListModel>
#include <QQmlContext>
class Generator : public QObject
{
Q_OBJECT
QStringListModel * m_model;
public:
Generator(QStringListModel * model) : m_model(model) {}
Q_INVOKABLE void generate(const QVariant & val) {
QStringList list;
for (int i = 1; i <= 3; ++i) {
list << QString("%1:%2").arg(val.toString()).arg(i);
}
m_model->setStringList(list);
}
};
int main(int argc, char *argv[])
{
QStringListModel model1, model2;
Generator generator(&model2);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
QStringList list;
list << "one" << "two" << "three" << "four";
model1.setStringList(list);
engine.rootContext()->setContextProperty("model1", &model1);
engine.rootContext()->setContextProperty("model2", &model2);
engine.rootContext()->setContextProperty("generator", &generator);
engine.load(QUrl("qrc:/main.qml"));
QObject *topLevel = engine.rootObjects().value(0);
QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
window->show();
return app.exec();
}
#include "main.moc"
This is actually more of an answer/comment to the answer of @KubaOber. 实际上,这更多是对@KubaOber答案的回答/评论。
I found that it is actually not necessary to do any special tricks using multiple roles if you bind to the correct event: 我发现如果绑定到正确的事件,实际上没有必要使用多个角色来做任何特殊的技巧:
onAccepted: model.edit = text
works just fine and does not create any update loop (as it is only called on "human"/input modification). 可以正常工作,并且不会创建任何更新循环(因为仅在“人工” /输入修改时调用它)。
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