QVBoxLayout: How to vertically align widgets to the top instead of the center

问题

In Qt, When I add widgets to my layout, they are vertically centered by default. Is there a way to "List" the widgets from top to bottom instead of centering them vertically?

回答1:

use void QLayout::setAlignment ( Qt::Alignment alignment ) method to set alignment according to your choice.

回答2:

I find this a little more complicated than just using layout.setAlignment(). It kept not working for me until just now, when I figured out that if you have expanding widgets that you set a maximum height for, then that widget will not be aligned the way you want.

Here is example code that does not top align the QTextBrowser() widget even though I call layout.setAlignment(Qt.AlignTop). Sorry that it is in Python, but it is pretty easy to translate to C++ (I have gone the other way many times).

from PyQt4.QtCore import *
from PyQt4.QtGui import *

class MyWidget(QWidget):
    """
    Create a widget that aligns its contents to the top.
    """

    def __init__(self, parent=None):

        QWidget.__init__(self, parent)

        layout = QVBoxLayout()

        label = QLabel('label:')
        layout.addWidget(label)

        info = QTextBrowser(self)
        info.setMinimumHeight(100)
        info.setMaximumHeight(200)
        layout.addWidget(info)        
        # Uncomment the next line to get this to align top.
#         layout.setAlignment(info, Qt.AlignTop)

        # Create a progress bar layout.
        button = QPushButton('Button 1')        
        layout.addWidget(button)        

        # This will align all the widgets to the top except
        # for the QTextBrowser() since it has a maximum size set.
        layout.setAlignment(Qt.AlignTop)

        self.setLayout(layout)


if __name__ == '__main__':

    import sys

    app = QApplication(sys.argv)

    widget = MyWidget()
    widget.show()
    widget.resize(QSize(900, 400))

    app.exec_()

The following explicitly calls layout.setAlignment(info, Qt.AlignTop) to get the expending text widget to work.

from PyQt4.QtCore import *
from PyQt4.QtGui import *

class MyWidget(QWidget):
    """
    Create a widget that aligns its contents to the top.
    """

    def __init__(self, parent=None):

        QWidget.__init__(self, parent)

        layout = QVBoxLayout()

        label = QLabel('label:')
        layout.addWidget(label)

        info = QTextBrowser(self)
        info.setMinimumHeight(100)
        info.setMaximumHeight(200)
        layout.addWidget(info)        
        # Uncomment the next line to get this to align top.
        layout.setAlignment(info, Qt.AlignTop)

        # Create a progress bar layout.
        button = QPushButton('Button 1')        
        layout.addWidget(button)        

        # This will align all the widgets to the top except
        # for the QTextBrowser() since it has a maximum size set.
        layout.setAlignment(Qt.AlignTop)

        self.setLayout(layout)


if __name__ == '__main__':

    import sys

    app = QApplication(sys.argv)

    widget = MyWidget()
    widget.show()
    widget.resize(QSize(900, 400))

    app.exec_()

回答3:

If you have a QVBoxLayout and want your fixed size widgets to be stacked at the top, you can simply append a vertical stretch add the end:

layout.addStretch()

If you have multiple stretchers or other stretch items, you can specify an integer stretch factor argument that defines their size ratio.

回答4:

After comparison between the two solutions, it seems that :

myLayout.setAlignment(Qt.AlignTop)

works for several widget alignement but :

myLayout.setAlignment(myWidget, Qt.AlignTop)

works only for the first widget you add to the layout. After all, the solution depends also to the QSizePolicy of yours widgets.

来源：https://stackoverflow.com/questions/10082299/qvboxlayout-how-to-vertically-align-widgets-to-the-top-instead-of-the-center

标签

qlayout