Mouse Resizing cursor changes to normal in WPF?

Question

I have a WPF application, by default the resizing perfectly work. but as soon as I set the AllowsTransparency="True" the mouse resizing from edges and corner of the application is completely gone. I need to set AllowsTransparency="True" because if it's set to "False" then a white border comes at the top of the window.

To fix this issue I give border at every four edges and give some resizing event handler to them. The problem is appear on two border. The problem is, while I drag the edges to resize the cursor changes to normal. How I overcome this issue?

Answer 1

Here is an example of resizing the window, you could see if it can work for you successfully.
MainWindow.xaml:

<Window x:Class="ResizeWindow.MainWindow"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:ResizeWindow" Name="window"    
        mc:Ignorable="d" AllowsTransparency="True" WindowStyle="None" ResizeMode="NoResize"   
        Title="MainWindow" Height="450" Width="800">  
    <Window.Resources>  
        <Style x:Key="RectBorderStyle" TargetType="Rectangle">  
            <Setter Property="Focusable" Value="False" />  
            <Setter Property="Fill" Value="Transparent" />  
            <Setter Property="Tag" Value="{Binding RelativeSource={RelativeSource AncestorType=Window}}" />  
            <EventSetter Event="MouseLeftButtonDown" Handler="Resize_Init"/>  
            <EventSetter Event="MouseLeftButtonUp" Handler="Resize_End"/>  
            <EventSetter Event="MouseMove" Handler="Resizeing_Window"/>  
        </Style>  
    </Window.Resources>  
    <Grid>  
        <Rectangle x:Name="leftSizeGrip" Width="7" HorizontalAlignment="Left" Cursor="SizeWE"  Style="{StaticResource RectBorderStyle}" />  
        <Rectangle x:Name="rightSizeGrip"  Width="7"  HorizontalAlignment="Right"  Cursor="SizeWE"  Style="{StaticResource RectBorderStyle}" />  
        <Rectangle x:Name="topSizeGrip" Height="7" VerticalAlignment="Top" Cursor="SizeNS"  Style="{StaticResource RectBorderStyle}" />  
        <Rectangle x:Name="bottomSizeGrip"   Height="7" VerticalAlignment="Bottom"   Cursor="SizeNS" Style="{StaticResource RectBorderStyle}" />  
        <Rectangle Name="bottomRighttSizeGrip"  Width="7"  Height="7" HorizontalAlignment="Right" VerticalAlignment="Bottom" Cursor="SizeNWSE" Style="{StaticResource RectBorderStyle}" />  

    </Grid>  
</Window>  

The result:

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Answer 2

I failed to fill MainWindow,xaml.cs in the answer, I filled it in the comment.
MainWindow,xaml.cs:

bool ResizeInProcess = false;  
    private void Resize_Init(object sender, MouseButtonEventArgs e)  
    {  
      Rectangle senderRect = sender as Rectangle;  
      if (senderRect != null)  
      {  
        ResizeInProcess = true;  
        senderRect.CaptureMouse();  
      }  
    }  
    private void Resize_End(object sender, MouseButtonEventArgs e)  
    {  
      Rectangle senderRect = sender as Rectangle;  
      if (senderRect != null)  
      {  
        ResizeInProcess = false; ;  
        senderRect.ReleaseMouseCapture();  
      }  
    }  
    private void Resizeing_Window(object sender, MouseEventArgs e)  
    {  
      if (ResizeInProcess)  
      {  
        Rectangle senderRect = sender as Rectangle;  
        Window mainWindow = senderRect.Tag as Window;  
        if (senderRect != null)  
        {  
          double width = e.GetPosition(mainWindow).X;  
          double height = e.GetPosition(mainWindow).Y;  
          senderRect.CaptureMouse();  
          if (senderRect.Name.ToLower().Contains("right"))  
          {  
            width += 5;  
            if (width > 0)  
              mainWindow.Width = width;  
          }  
          if (senderRect.Name.ToLower().Contains("left"))  
          {  
            width -= 5;  
            mainWindow.Left += width;  
            width = mainWindow.Width - width;  
            if (width > 0)  
            {  
              mainWindow.Width = width;  
            }  
          }  
          if (senderRect.Name.ToLower().Contains("bottom"))  
          {  
            height += 5;  
            if (height > 0)  
              mainWindow.Height = height;  
          }  
          if (senderRect.Name.ToLower().Contains("top"))  
          {  
            height -= 5;  
            mainWindow.Top += height;  
            height = mainWindow.Height - height;  
            if (height > 0)  
            {  
              mainWindow.Height = height;  
            }  
          }  
        }  
      }  
    }  

update:

Base on my search, you could use a transparent window to avoid this problem. First maximize the transparent window, and then put the content in the Canvas.
Users will not know that what they see on the screen is not a real "window."
MainWindow.xaml:

<Window x:Class="windowResizeProblem.MainWindow"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:windowResizeProblem"  
        mc:Ignorable="d"  
        Title="MainWindow" Height="450" Width="800"   
        WindowStyle="None" WindowState="Maximized"   
        Background="Transparent" AllowsTransparency="True">  
    <Canvas>  
        <Border x:Name="Content" Canvas.Left="500" Canvas.Top="500" Width="500" Height="500"   
                MinWidth="100" MinHeight="100" CornerRadius="2"   Background="AliceBlue">  
            <Border.Effect>  
                <DropShadowEffect ShadowDepth="0" BlurRadius="10"/>  
            </Border.Effect>  
            <Grid>  
                <Grid.ColumnDefinitions>  
                    <ColumnDefinition Width="4" />  
                    <ColumnDefinition Width="*" />  
                    <ColumnDefinition Width="4" />  
                </Grid.ColumnDefinitions>  
                <Grid.RowDefinitions>  
                    <RowDefinition Height="4" />  
                    <RowDefinition Height="Auto" />  
                    <RowDefinition Height="*" />  
                    <RowDefinition Height="4" />  
                </Grid.RowDefinitions>  
                <Thumb x:Name="topSizeGrip" Opacity="0" Grid.Row="0" Grid.Column="1" Cursor="SizeNS"  DragDelta="Thumb_DragDelta"/>  
                <Thumb x:Name="bottomSizeGrip" Opacity="0" Grid.Row="3" Grid.Column="1" Cursor="SizeNS"  DragDelta="Thumb_DragDelta"/>  
                <Thumb x:Name="leftSizeGrip" Opacity="0" Grid.Row="1" Grid.Column="0" Grid.RowSpan="2" Cursor="SizeWE" DragDelta="Thumb_DragDelta"/>  
                <Thumb x:Name="rightSizeGrip" Opacity="0" Grid.Row="1" Grid.Column="2" Grid.RowSpan="2" Cursor="SizeWE" DragDelta="Thumb_DragDelta"/>  
                <Thumb x:Name="bottomRightSizeGrip" Opacity="0" Grid.Row="3" Grid.Column="2" Cursor="SizeNWSE" Tag="BR" DragDelta="Thumb_DragDelta"/>  
                <Border Grid.Row="2" Grid.Column="1" CornerRadius="3" BorderThickness="1" BorderBrush="LightSeaGreen" Background="LightGoldenrodYellow">  
                    <TextBlock Text="my window" FontSize="20" HorizontalAlignment="Center" VerticalAlignment="Center"/>  
                </Border>  
            </Grid>  
        </Border>  
    </Canvas>  
</Window>  

MainWindow.xaml.cs:

using System;  
using System.Windows;  
using System.Windows.Controls;  
using System.Windows.Controls.Primitives;  
  
namespace windowResizeProblem  
{  
  public partial class MainWindow : Window  
  {  
    public MainWindow()  
    {  
      InitializeComponent();  
    }  
    private void Thumb_DragDelta(object sender, DragDeltaEventArgs e)  
    {  
      var str = (string)((Thumb)sender).Name.ToLower();  
  
      if (str.Contains("top"))  
      {  
        Content.Height = Math.Min(Math.Max(Content.MinHeight, Content.ActualHeight - e.VerticalChange), Content.MaxHeight);  
        Canvas.SetTop(Content, Canvas.GetTop(Content) - Content.Height + Content.ActualHeight);  
      }  
      if (str.Contains("left"))  
      {  
        Content.Width = Math.Min(Math.Max(Content.MinWidth, Content.ActualWidth - e.HorizontalChange), Content.MaxWidth);  
        Canvas.SetLeft(Content, Canvas.GetLeft(Content) - Content.Width + Content.ActualWidth);  
      }  
      if (str.Contains("bottom"))  
      {  
        Content.Height = Math.Min(Math.Max(Content.MinHeight, Content.ActualHeight + e.VerticalChange), Content.MaxHeight);  
      }  
      if (str.Contains("right"))  
      {  
        Content.Width = Math.Min(Math.Max(Content.MinWidth, Content.ActualWidth + e.HorizontalChange), Content.MaxWidth);  
      }  
      e.Handled = true;  
    }  
  }  
}  

The result: