在 C++ 應用程序使用 Designer UI 文件

Qt Designer UI 文件以 XML 格式錶示 Widget 錶單樹。錶單可以被處理：

在編譯時，意味著錶單將被轉換成可以編譯的 C++ 代碼。
在運行時，意味著錶單的處理是通過 QUiLoader 類，動態構建 Widget 樹當剖析 XML 文件時。

編譯時錶單處理

創建用戶界麵組件采用 Qt Designer 和使用 Qt 集成構建工具， qmake and uic ，當構建應用程序時為它們生成代碼。生成代碼包含錶單用戶界麵對象。它是 C++ 結構，包含：

指嚮錶單 Widget、布局、布局項、按鈕組及動作的指針。
成員函數調用 setupUi() 以在父級 Widget 構建小部件樹。
成員函數調用 retranslateUi() 處理錶單字符串特性的翻譯。更多信息，見應對語言變化 .

生成代碼可以包括在應用程序中且能直接使用。另外，可以使用它來擴展標準 Widget 的子類。

編譯時處理錶單可以按下列方法之一用於應用程序：

直接方式：構造 Widget 用作組件占位符，並在其中設置用戶界麵。
單繼承方式：子類錶單基類 ( QWidget or QDialog ，例如)，並包括錶單用戶界麵對象的私有實例。
多繼承方式：子類錶單基類和錶單用戶界麵對象兩者。這允許在子類作用域內，直接使用錶單定義 Widget。

為演示，我們創建簡單 Calculator Form 應用程序。基於原始計算器錶單範例。

應用程序的組成由一源文件， main.cpp 和 UI 文件。

The calculatorform.ui 文件設計采用 Qt Designer 展示如下：

將使用 qmake to build the executable, so we need to write a .pro 文件：

HEADERS     = calculatorform.h

此文件的特殊特徵是 FORMS 聲明，告訴 qmake 要處理文件采用 uic 。在此情況下， calculatorform.ui 文件被用來創建 ui_calculatorform.h 文件，可以用於的任何文件列齣在 SOURCES 聲明。

注意： You can use Qt Creator to create the Calculator Form project. It automatically generates the main.cpp, UI, and .pro files, which you can then modify.

直接方式

為以直接方式使用，包括 ui_calculatorform.h 文件直接在 main.cpp :

#include "ui_calculatorform.h"

The main 函數創建 Calculator 小部件通過構造標準 QWidget 用於托管用戶界麵描述通過 calculatorform.ui 文件。

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QWidget widget;
    Ui::CalculatorForm ui;
    ui.setupUi(&widget);
    widget.show();
    return app.exec();
}

在此情況下， Ui::CalculatorForm 是界麵描述對象來自 ui_calculatorform.h 文件，設置所有對話框的 Widget 和在其信號與槽之間的連接。

The direct approach provides a quick and easy way to use simple, self-contained components in your applications. However, componens created with Qt Designer often require close integration with the rest of the application code. For instance, the CalculatorForm code provided above will compile and run, but the QSpinBox objects will not interact with the QLabel as we need a custom slot to carry out the add operation and display the result in the QLabel . To achieve this, we need to use the single inheritance approach.

單繼承方式

為以單繼承方式使用，子類標準 Qt 小部件，並包括錶單用戶界麵對象的私有實例。

成員變量
指針成員變量

使用成員變量

In this approach, we subclass a Qt widget and set up the user interface from within the constructor. Components used in this way expose the widgets and layouts used in the form to the Qt widget subclass, and provide a standard system for making signal and slot connections between the user interface and other objects in your application. The generated Ui::CalculatorForm structure is a member of the class.

This approach is used in the 計算器錶單範例。

To ensure that we can use the user interface, we need to include the header file that uic generates before referring to Ui::CalculatorForm :

#include "ui_calculatorform.h"

This means that the .pro file must be updated to include calculatorform.h :

HEADERS     = calculatorform.h

按以下方式定義子類：

class CalculatorForm : public QWidget
{
    Q_OBJECT
public:
    explicit CalculatorForm(QWidget *parent = nullptr);
private slots:
    void on_inputSpinBox1_valueChanged(int value);
    void on_inputSpinBox2_valueChanged(int value);
private:
    Ui::CalculatorForm ui;
};

The important feature of the class is the private ui object which provides the code for setting up and managing the user interface.

The constructor for the subclass constructs and configures all the widgets and layouts for the dialog just by calling the ui 對象的 setupUi() function. Once this has been done, it is possible to modify the user interface as needed.

CalculatorForm::CalculatorForm(QWidget *parent)
    : QWidget(parent)
{
    ui.setupUi(this);
}

We can connect signals and slots in user interface widgets in the usual way by adding the on_<object name> - prefix. For more information, see widgets-and-dialogs-with-auto-connect .

The advantages of this approach are its simple use of inheritance to provide a QWidget -based interface, and its encapsulation of the user interface widget variables within the ui data member. We can use this method to define a number of user interfaces within the same widget, each of which is contained within its own namespace, and overlay (or compose) them. This approach can be used to create individual tabs from existing forms, for example.

使用指針成員變量

另外， Ui::CalculatorForm structure can be made a pointer member of the class. The header then looks as follows:

namespace Ui {
    class CalculatorForm;
}
class CalculatorForm : public QWidget
...
virtual ~CalculatorForm();
...
private:
    Ui::CalculatorForm *ui;
...

相應源文件看起來如下：

#include "ui_calculatorform.h"
CalculatorForm::CalculatorForm(QWidget *parent) :
    QWidget(parent), ui(new Ui::CalculatorForm)
{
    ui->setupUi(this);
}
CalculatorForm::~CalculatorForm()
{
    delete ui;
}

The advantage of this approach is that the user interface object can be forward-declared, which means that we do not have to include the generated ui_calculatorform.h file in the header. The form can then be changed without recompiling the dependent source files. This is particularly important if the class is subject to binary compatibility restrictions.

We generally recommend this approach for libraries and large applications. For more information, see 創建共享庫 .

多繼承方式

錶單創建采用 Qt Designer 可以子類化在一起采用標準 QWidget 基類。此方式製作由錶單定義的所有用戶界麵組件 (可在子類作用域內直接訪問)，並啓用信號和槽連接按通常方式采用 connect() 函數。

This approach is used in the Multiple Inheritance 範例。

需要包括頭文件由 uic 生成自 calculatorform.ui 文件，如下：

#include "ui_calculatorform.h"

The class is defined in a similar way to the one used in the 單繼承方式 , except that this time we inherit from both QWidget and Ui::CalculatorForm ，如下：

class CalculatorForm : public QWidget, private Ui::CalculatorForm
{
    Q_OBJECT
public:
    explicit CalculatorForm(QWidget *parent = nullptr);
private slots:
    void on_inputSpinBox1_valueChanged(int value);
    void on_inputSpinBox2_valueChanged(int value);
};

繼承 Ui::CalculatorForm privately to ensure that the user interface objects are private in our subclass. We can also inherit it with the public or protected keywords in the same way that we could have made ui public or protected in the previous case.

The constructor for the subclass performs many of the same tasks as the constructor used in the 單繼承範例：

CalculatorForm::CalculatorForm(QWidget *parent)
    : QWidget(parent)
{
    setupUi(this);
}

In this case, the widgets used in the user interface can be accessed in the same say as a widget created in code by hand. We no longer require the ui prefix to access them.

應對語言變化

Qt 通知應用程序，若用戶界麵語言變化通過發送事件類型 QEvent::LanguageChange 。要調用成員函數 retranslateUi() 對於用戶界麵對象，重實現 QWidget::changeEvent() 在錶單類中，如下所示：

void CalculatorForm::changeEvent(QEvent *e)
{
    QWidget::changeEvent(e);
    switch (e->type()) {
    case QEvent::LanguageChange:
        ui->retranslateUi(this);
        break;
    default:
        break;
   }
}

運行時處理錶單

另外，可以在運行時處理錶單，産生動態生成用戶界麵。這的完成可以使用 QtUiTools 模塊提供 QUiLoader 類以處理錶單創建采用 Qt Designer .

UiTools 方式

A resource file containing a UI file is required to process forms at run time. Also, the application needs to be configured to use the QtUiTools module. This is done by including the following declaration in a qmake project file, ensuring that the application is compiled and linked appropriately.

QT += uitools

The QUiLoader class provides a form loader object to construct the user interface. This user interface can be retrieved from any QIODevice ，如 QFile object, to obtain a form stored in a project's resource file. The QUiLoader::load () 函數使用文件中包含的用戶界麵描述構造錶單 Widget。

The QtUiTools 模塊類可以被包括使用以下指令：

#include <QtUiTools>

The QUiLoader::load () 函數的援引如此代碼所展示的來自文本查找器範例：

static QWidget *loadUiFile(QWidget *parent)
{
    QFile file(":/forms/textfinder.ui");
    file.open(QIODevice::ReadOnly);
    QUiLoader loader;
    return loader.load(&file, parent);
}

In a class that uses QtUiTools to build its user interface at run time, we can locate objects in the form using QObject::findChild (). For example, in the following code, we locate some components based on their object names and widget types:

    ui_findButton = findChild<QPushButton*>("findButton");
    ui_textEdit = findChild<QTextEdit*>("textEdit");
    ui_lineEdit = findChild<QLineEdit*>("lineEdit");

Processing forms at run-time gives the developer the freedom to change a program's user interface, just by changing the UI file. This is useful when customizing programs to suit various user needs, such as extra large icons or a different colour scheme for accessibility support.

自動連接

The signals and slots connections defined for compile time or run time forms can either be set up manually or automatically, using QMetaObject 's ability to make connections between signals and suitably-named slots.

Generally, in a QDialog , if we want to process the information entered by the user before accepting it, we need to connect the clicked() signal from the OK button to a custom slot in our dialog. We will first show an example of the dialog in which the slot is connected by hand then compare it with a dialog that uses automatic connection.

對話框不采用自動連接

We define the dialog in the same way as before, but now include a slot in addition to the constructor:

class ImageDialog : public QDialog, private Ui::ImageDialog
{
    Q_OBJECT
public:
    ImageDialog(QWidget *parent = 0);
private slots:
    void checkValues();
};

The checkValues() slot will be used to validate the values provided by the user.

In the dialog's constructor we set up the widgets as before, and connect the Cancel 按鈕的 clicked() signal to the dialog's reject() slot. We also disable the autoDefault property in both buttons to ensure that the dialog does not interfere with the way that the line edit handles return key events:

ImageDialog::ImageDialog(QWidget *parent)
    : QDialog(parent)
{
    setupUi(this);
    okButton->setAutoDefault(false);
    cancelButton->setAutoDefault(false);
    ...
    connect(okButton, SIGNAL(clicked()), this, SLOT(checkValues()));
}

連接 OK 按鈕的 clicked() signal to the dialog's checkValues() slot which we implement as follows:

void ImageDialog::checkValues()
{
    if (nameLineEdit->text().isEmpty())
        (void) QMessageBox::information(this, tr("No Image Name"),
            tr("Please supply a name for the image."), QMessageBox::Cancel);
    else
        accept();
}

This custom slot does the minimum necessary to ensure that the data entered by the user is valid - it only accepts the input if a name was given for the image.

Widget 和對話框采用自動連接

Although it is easy to implement a custom slot in the dialog and connect it in the constructor, we could instead use QMetaObject 's auto-connection facilities to connect the OK button's clicked() signal to a slot in our subclass. uic automatically generates code in the dialog's setupUi() function to do this, so we only need to declare and implement a slot with a name that follows a standard convention:

void on_<object name>_<signal name>(<signal parameters>);

Using this convention, we can define and implement a slot that responds to mouse clicks on the OK 按鈕：

class ImageDialog : public QDialog, private Ui::ImageDialog
{
    Q_OBJECT
public:
    ImageDialog(QWidget *parent = 0);
private slots:
    void on_okButton_clicked();
};

Another example of automatic signal and slot connection would be the 文本查找器采用其 on_findButton_clicked() 槽。

使用 QMetaObject 係統以啓用信號和槽連接：

    QMetaObject::connectSlotsByName(this);

This enables us to implement the slot, as shown below:

void TextFinder::on_findButton_clicked()
{
    QString searchString = ui_lineEdit->text();
    QTextDocument *document = ui_textEdit->document();
    bool found = false;
    // undo previous change (if any)
    document->undo();
    if (searchString.isEmpty()) {
        QMessageBox::information(this, tr("Empty Search Field"),
                                 tr("The search field is empty. "
                                    "Please enter a word and click Find."));
    } else {
        QTextCursor highlightCursor(document);
        QTextCursor cursor(document);
        cursor.beginEditBlock();
    ...
        cursor.endEditBlock();
        if (found == false) {
            QMessageBox::information(this, tr("Word Not Found"),
                                     tr("Sorry, the word cannot be found."));
        }
    }
}

Automatic connection of signals and slots provides both a standard naming convention and an explicit interface for widget designers to work to. By providing source code that implements a given interface, user interface designers can check that their designs actually work without having to write code themselves.