Qt findChild返回0 [英] Qt findChild returning 0
问题描述
我目前正在使用一个很好的方法来使用GUI修改对象内容在运行时,项目使用Qt。
所以我想传递一个QLayout对象,让他们创建自己的GUI。作为POC,我创建了这个(display是QVBoxLayout *参数的名称):
QPushButton * button = new QPushButton ();
button-> setText(foo);
button-> setObjectName(bar);
display-> addWidget(button);
它的工作原理与预期一样好。但是我需要读取用户键入的GuI,所以这是我做的下一步:
QPushButton * button2 = display-> findChild< QPushButton *>();
if(button2)
std :: cout<< button2-> objectName()。toStdString()<< std :: endl;
这里没有输出任何内容 - if()语句为false!
QList< QWidget *> widgets = display-> findChildren< QWidget *>();
foreach(QWidget * b,widgets){
std :: cout<< b-> objectName()。toStdString()<< std :: endl;类似地,窗口小部件列表为空。
$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $
$ b 我尝试通过 http ://doc.qt.digia.com/qt/qvboxlayout-members.html ,但findChild / findChildren似乎最适合我的需要...
最好的问候,
LDer
解决方案
这是我现在处理的方式:
而不是传递一个QVBoxLayout到GUI创建,一个QWidget应该传递,显示。
QVBoxLayout * layout = new QVBoxLayout();
display-> setLayout(layout);
QPushButton * button = new QPushButton();
button-> setText(foo);
button-> setObjectName(bar);
layout-> addWidget(button);
现在到findChild / findChildren:
QPushButton * button2 = display-> findChild< QPushButton *>(bar);
if(button2)
std :: cout<< button2-> objectName()。toStdString()<< std :: endl;
QList< QWidget *> widgets = display-> findChildren< QWidget *>();
foreach(QWidget * b,widgets){
std :: cout<< b-> objectName()。toStdString()<< std :: endl;
}
这两种方法对我都有效。
对Slavik81的感谢
解决方案 QWidget
的父级必须是 QWidget
。 QLayout
不是 QWidget
。
移动并调整 QWidget
的子项。虽然您可以通过在布局上调用来添加子窗口小部件,但最终,它们的父窗口将是布局所在的 QWidget
。
说明:
QWidget * widget = new QWidget;
qDebug(Widget:%p,widget);
QHBoxLayout * layout = new QHBoxLayout;
qDebug(Layout:%p,layout);
QWidget * child = new QWidget;
layout-> addWidget(child);
qDebug(setLayout:%p之前的子级父级,child-> parent());
widget-> setLayout(layout);
qDebug(setLayout:%p之后的子级父级,child-> parent());
输出:
code> Widget:0x8e1c1e0
布局:0x8e1c3f0
setLayout之前的子级父级:0x0
setLayout后的子级父级:0x8e1c1e0
I'm currently working on a nice way to use a GUI to modify object contents at runtime, project uses Qt.
So I thought of passing a QLayout to the objects, to let them create their own GUI. As POC, I created this ("display" is the name of the QVBoxLayout* parameter):
QPushButton* button = new QPushButton();
button->setText("foo");
button->setObjectName("bar");
display->addWidget(button);
which works just as fine as expected. But I will need to read what the user typed into the GuI, so this is what I did next:
QPushButton *button2 = display->findChild<QPushButton *>();
if(button2)
std::cout << button2->objectName().toStdString() << std::endl;
here nothing is put out - if() statement is false!
QList<QWidget *> widgets = display->findChildren<QWidget *>();
foreach (QWidget* b, widgets) {
std::cout << b->objectName().toStdString() << std::endl;
}
similarly, the "widgets" list is empty.
I tried looking through the full member list at http://doc.qt.digia.com/qt/qvboxlayout-members.html, but findChild/findChildren seems like the best fit to my needs...
Best regards, LDer
SOLUTION BELOW
This is how I handle it now:
instead of passing a QVBoxLayout to the GUI creation, a QWidget should be passed, in following named "display" as above.
QVBoxLayout* layout = new QVBoxLayout();
display->setLayout(layout);
QPushButton* button = new QPushButton();
button->setText("foo");
button->setObjectName("bar");
layout->addWidget(button);
now to findChild / findChildren:
QPushButton *button2 = display->findChild<QPushButton *>("bar");
if(button2)
std::cout << button2->objectName().toStdString() << std::endl;
QList<QWidget *> widgets = display->findChildren<QWidget *>();
foreach (QWidget* b, widgets) {
std::cout << b->objectName().toStdString() << std::endl;
}
both methods work for me as expected! (Plus, now the layout can be chosen freely by the GUI creation!)
Kudos to Slavik81
The parent of a QWidget
must be a QWidget
. QLayout
is not a QWidget
.
Layouts exist to move and resize the children of a QWidget
. Though you may add child widgets by making calls on the layout, ultimately, their parent will be the QWidget
that the layout resides on.
To illustrate:
QWidget* widget = new QWidget;
qDebug("Widget: %p", widget);
QHBoxLayout* layout = new QHBoxLayout;
qDebug("Layout: %p", layout);
QWidget* child = new QWidget;
layout->addWidget(child);
qDebug("Child's parent before setLayout: %p", child->parent());
widget->setLayout(layout);
qDebug("Child's parent after setLayout: %p", child->parent());
Output:
Widget: 0x8e1c1e0
Layout: 0x8e1c3f0
Child's parent before setLayout: 0x0
Child's parent after setLayout: 0x8e1c1e0
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