WPF window centering & change trigger mechanism

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Original author ： Tang, song, yuan, Ming and Qing Dynasties

Original address ：https://www.cnblogs.com/kybs0/p/7420767.html

Center window & Change trigger mechanism

solve ：

1） Single instance window , Every time the window is hidden and then displayed , The position is centered

2） Multi screen single instance window , When the parent window moves to another screen , When the single instance window pops up again , The location is updated to the parent window screen .

3） Every time the child window wakes up , It's all centered .

Where the window first appears - WindowStartupLocation

Windows The start-up position of the is displayed ,WindowStartupLocation

• CenterOwner -- Display in the middle of the parent window （ Set up Owner)

• CenterScreen -- Displayed in the middle of the current screen

• Manual -- Default location When the first Window.ShowDialog when ,window Display the above settings .

Change trigger mechanism The above only covers the first display position , after , The position of the window will remain

How to set the window to pop up again after hiding , Show in the middle （CenterOwner/CenterScreen）？ How to set the window to stay in the middle ？

Let's get to know , What are the triggering mechanisms

• Activated Window activation When the window changes to the foreground window （ That is, it is displayed in the front ）, Will trigger

• IsVisibleChanged Show changes When we set the window to hide Hide() when ,IsVisibile=false. Window again ShowDialog when ,IsVisibile=true; Using the above two mechanisms , Now we can do something .

First define several enumerations ：

/// <summary>
    ///  The window displays the change trigger time 
    /// </summary>
    public enum WindowLocationInvokeOccasion
    {
        /// <summary>
        ///  as long as Activated Just in the middle 
        /// </summary>
        Activated = 0,

        /// <summary>
        ///  Only for the first time Activated when , Show once in the middle , Subsequent changes will not be modified 
        /// </summary>
        FirstActivated,

        /// <summary>
        ///  Every time the window is displayed , Center window 
        /// <para> It can solve the problem that the pop-up window of a single instance is not centered </para>
        /// </summary>
        Visibile,

        /// <summary>
        ///  Every time the window is displayed , If the parent window is not on the same screen as the current window , Center window 
        /// <para> It can solve the problem that the pop-up window of a single instance is not centered </para>
        /// </summary>
        VisibileInDifferentScreen,

        /// <summary>
        ///  Don't trigger 
        /// </summary>
        Defatult
    }

The above enumeration contains 4 There's a trigger mechanism .

Let's define an additional attribute , Set additional functions of the window through additional properties - The trigger mechanism is displayed in the center

/// <summary>
///  The window displays the center trigger timing 
/// <para> another ： Center display settings , Please use <see cref="Window"/> Of <see cref="WindowStartupLocation"/> attribute </para>
/// </summary>
public static readonly DependencyProperty InvokeOccasionProperty = DependencyProperty.RegisterAttached(
    "InvokeOccasion", typeof(WindowLocationInvokeOccasion), typeof(WindowLocationOptions),
    new PropertyMetadata(default(WindowLocationInvokeOccasion), InvokeOccasionProperty_ChangedCallback));

In the property change trigger event , According to different trigger conditions , Set different centered display .

• Activated -- as long as Activated Just in the middle Every time a trigger , Just display the window directly ;

• For the first time Activated By setting Window.Activated -= ShowInCenter_Activated; Disable next trigger entry

• Visibile

• VisibileInDifferentScreen When the window is displayed , If the parent window is not on the same screen as the current window , Center window . How to determine whether the current child window and the parent window are on the same screen ？

var screen = Screen.FromHandle(new WindowInteropHelper(parentWindow).Handle);

Graphics currentGraphics = Graphics.FromHwnd(new WindowInteropHelper(parentWindow).Handle);
double dpiXRatio = currentGraphics.DpiX / 96;
double dpiYRatio = currentGraphics.DpiY / 96;

// When the child window is on the same screen as the parent window , Do not deal with 
var isSubWindowInSameScreen = subWindow.Left > screen.Bounds.Left / dpiXRatio &&
                                subWindow.Left < screen.Bounds.Left / dpiXRatio + screen.Bounds.Width / dpiXRatio &&
                                subWindow.Top > screen.Bounds.Top / dpiYRatio &&
                                subWindow.Top < screen.Bounds.Top / dpiYRatio + screen.Bounds.Height / dpiYRatio;
return isSubWindowInSameScreen;

Describe the trigger conditions for completion , Now let's say that the window is centered . centered , It is divided into The current screen is centered / Center in the main window , Go straight to the code

1） Center in the main window -CenterOwner Set the position of the window Location(Left,Top)（ top left corner ）

• When child windows are maximized --WindowState=“Maximized” Maximization window , Fixed pop-up to the main screen , Therefore, additional treatment is required , According to the screen Location Set location ;

• When the parent window is maximized -- When the parent window is maximized , Of the parent window location, Due to window settings margin, It may not be accurate , So take the screen position

• CenterOwner The window is centered -- Take the position of the parent window directly / Size and sub window size , Just do the calculation ;
  PS: Window location Left/Top May be a negative

/// <summary>
///  Center in the main window 
/// </summary>
/// <param name="subWindow"></param>
/// <param name="parentWindow"></param>
private static void SetWindowInCenterOwner(Window subWindow, Window parentWindow)
{
    // Maximization window , Fixed pop-up to the main screen , Therefore, additional treatment is required 
    if (subWindow.WindowState == WindowState.Maximized)
    {
        // When child windows are maximized , You need to set the position according to the screen ;
        var screen = Screen.FromHandle(new WindowInteropHelper(parentWindow).Handle);

        Graphics currentGraphics = Graphics.FromHwnd(new WindowInteropHelper(parentWindow).Handle);
        double dpiXRatio = currentGraphics.DpiX / 96;
        double dpiYRatio = currentGraphics.DpiY / 96;

        subWindow.Left = screen.Bounds.Left / dpiXRatio;
        subWindow.Top = screen.Bounds.Top / dpiYRatio;
    }
    if (parentWindow.WindowState == WindowState.Maximized)
    {
        // When the parent window is maximized , Of the parent window location, Due to window settings margin, It may not be accurate , So take the screen position 
        var screen = Screen.FromHandle(new WindowInteropHelper(parentWindow).Handle);

        Graphics currentGraphics = Graphics.FromHwnd(new WindowInteropHelper(parentWindow).Handle);
        double dpiXRatio = currentGraphics.DpiX / 96;
        double dpiYRatio = currentGraphics.DpiY / 96;

        // The window is centered 
        subWindow.Left = screen.Bounds.Left / dpiXRatio +
                            (screen.Bounds.Width / dpiXRatio - subWindow.ActualWidth) / 2;
        subWindow.Top = screen.Bounds.Top / dpiYRatio +
                        (screen.Bounds.Height / dpiYRatio - subWindow.ActualHeight) / 2;
    }
    else
    {
        // The window is centered 
        subWindow.Left = parentWindow.Left + (parentWindow.ActualWidth - subWindow.ActualWidth) / 2;
        subWindow.Top = parentWindow.Top + (parentWindow.ActualHeight - subWindow.ActualHeight) / 2;
    }
}

2） The current screen is centered -CenterScreen;

• The window position setting is the same as above , It is worth noting that DPI.

• adopt win Display settings for , Adjust the text display scale , Screen position conversion (X,Y)``, We have to think about it DPI` Conversion of ;

/// <summary>
///  Display in the center of the screen where the parent window is located 
/// </summary>
/// <param name="subWindow"></param>
/// <param name="parentWindow"></param>
private static void SetWindowInCenterScreen(Window subWindow, Window parentWindow)
{
    SetWindowLocationInScreen(subWindow, parentWindow, subWindow.WindowState);
}

private const int DpiPercent = 96;

private static void SetWindowLocationInScreen(Window subWindow, Window parentWindow, WindowState windowState)
{
    var intPtr = new WindowInteropHelper(parentWindow).Handle;
    var screen = Screen.FromHandle(intPtr);

    using (Graphics currentGraphics = Graphics.FromHwnd(intPtr))
    {
        double dpiXRatio = currentGraphics.DpiX / DpiPercent;
        double dpiYRatio = currentGraphics.DpiY / DpiPercent;

        if (windowState == WindowState.Maximized)
        {
            // Set full screen Location
            subWindow.Left = screen.Bounds.Left / dpiXRatio;
            subWindow.Top = screen.Bounds.Top / dpiYRatio;
        }
        else
        {
            // Set center Location
            subWindow.Left = screen.Bounds.Left / dpiXRatio +
                                (screen.Bounds.Width / dpiXRatio - subWindow.ActualWidth) / 2;
            subWindow.Top = screen.Bounds.Top / dpiYRatio +
                            (screen.Bounds.Height / dpiYRatio - subWindow.ActualHeight) / 2;
        }
    }
}