Expanding lineEdit in QHBoxLayout is not working properly in qt plugins

[alizadeh91]

HI,
I've created a qt plugin with comboBox and lineEdit and put them in QHBoxLayout in Qt5. when i set sizepolicy of lineEdit to expanding, it doesn't works properly. actually it expands itself a little:
Untitled-4.png

my code in plugin constructor is something like below:

comboBox = new QComboBox;
    lineEditValue = new QLineEdit;
 
    horizontalLayout = new QHBoxLayout(this);
    horizontalLayout->setMargin(1);
 
    comboBox->setSizePolicy(QSizePolicy::Preferred,QSizePolicy::Fixed);
    lineEditValue->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Fixed);
 
    horizontalLayout->addWidget(lineEditValue,0,Qt::AlignLeft);
    horizontalLayout->addWidget(comboBox,0,Qt::AlignRight);
 
    this->setLayout(horizontalLayout);

comboBox = new QComboBox;
    lineEditValue = new QLineEdit;

    horizontalLayout = new QHBoxLayout(this);
    horizontalLayout->setMargin(1);

    comboBox->setSizePolicy(QSizePolicy::Preferred,QSizePolicy::Fixed);
    lineEditValue->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Fixed);

    horizontalLayout->addWidget(lineEditValue,0,Qt::AlignLeft);
    horizontalLayout->addWidget(comboBox,0,Qt::AlignRight);

    this->setLayout(horizontalLayout);

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what i am missing?