ComboBoxRenderer.DrawDropDownButton 方法

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

使用操作系统当前视觉样式绘制一个下拉箭头。

public:
 static void DrawDropDownButton(System::Drawing::Graphics ^ g, System::Drawing::Rectangle bounds, System::Windows::Forms::VisualStyles::ComboBoxState state);

public static void DrawDropDownButton (System.Drawing.Graphics g, System.Drawing.Rectangle bounds, System.Windows.Forms.VisualStyles.ComboBoxState state);

static member DrawDropDownButton : System.Drawing.Graphics * System.Drawing.Rectangle * System.Windows.Forms.VisualStyles.ComboBoxState -> unit

Public Shared Sub DrawDropDownButton (g As Graphics, bounds As Rectangle, state As ComboBoxState)

参数

g

Graphics

用于绘制下拉箭头的 Graphics。

bounds

Rectangle

用于指定下拉箭头边界的 Rectangle。

state

ComboBoxState

ComboBoxState 值之一，指定下拉箭头的可视状态。

例外

InvalidOperationException

操作系统不支持视觉样式。

- 或 -

用户在操作系统中禁用视觉样式。

- 或 -

视觉样式不应用于应用程序窗口的工作区。

示例

下面的代码示例在自定义控件的 OnPaint 方法中使用 DrawDropDownButton 方法，在由鼠标指针的位置确定的状态中绘制下拉箭头。 此代码示例是为 ComboBoxRenderer 类提供的一个更大示例的一部分。

      // Draw the combo box in the current state.
protected:
    virtual void OnPaint(PaintEventArgs^ e) override 
    {
        Control::OnPaint(e);

        if (!ComboBoxRenderer::IsSupported)
        {
            this->Parent->Text = "Visual Styles Disabled";
            return;
        }

        this->Parent->Text = "CustomComboBox Enabled";

        // Always draw the main text box and drop down arrow in their
        // current states
        ComboBoxRenderer::DrawTextBox(e->Graphics, topTextBoxRectangle,
            this->Text, this->Font, textBoxState);
        ComboBoxRenderer::DrawDropDownButton(e->Graphics, arrowRectangle,
            arrowState);

        // Only draw the bottom text box if the arrow has been clicked
        if (isActivated)
        {
            ComboBoxRenderer::DrawTextBox(e->Graphics,
                bottomTextBoxRectangle, bottomText, this->Font,
                textBoxState);
        }
    }

protected:
    virtual void OnMouseDown(MouseEventArgs^ e) override 
    {
        Control::OnMouseDown(e);

        // Check whether the user clicked the arrow.
        if (arrowRectangle.Contains(e->Location) &&
            ComboBoxRenderer::IsSupported)
        {
            // Draw the arrow in the pressed state.
            arrowState = ComboBoxState::Pressed;

            // The user has activated the combo box.
            if (!isActivated)
            {
                this->Text = "Clicked!";
                textBoxState = ComboBoxState::Pressed;
                isActivated = true;
            }

            // The user has deactivated the combo box.
            else
            {
                this->Text = "Click here";
                textBoxState = ComboBoxState::Normal;
                isActivated = false;
            }

            // Redraw the control.
            Invalidate();
        }
    }

// Draw the combo box in the current state.
protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);

    if (!ComboBoxRenderer.IsSupported)
    {
        this.Parent.Text = "Visual Styles Disabled";
        return;
    }

    this.Parent.Text = "CustomComboBox Enabled";

    // Always draw the main text box and drop down arrow in their 
    // current states
    ComboBoxRenderer.DrawTextBox(e.Graphics, topTextBoxRectangle,
        this.Text, this.Font, textBoxState);
    ComboBoxRenderer.DrawDropDownButton(e.Graphics, arrowRectangle,
        arrowState);

    // Only draw the bottom text box if the arrow has been clicked
    if (isActivated)
    {
        ComboBoxRenderer.DrawTextBox(e.Graphics,
            bottomTextBoxRectangle, bottomText, this.Font,
            textBoxState);
    }
}

protected override void OnMouseDown(MouseEventArgs e)
{
    base.OnMouseDown(e);

    // Check whether the user clicked the arrow.
    if (arrowRectangle.Contains(e.Location) &&
        ComboBoxRenderer.IsSupported)
    {
        // Draw the arrow in the pressed state.
        arrowState = ComboBoxState.Pressed;

        // The user has activated the combo box.
        if (!isActivated)
        {
            this.Text = "Clicked!";
            textBoxState = ComboBoxState.Pressed;
            isActivated = true;
        }

        // The user has deactivated the combo box.
        else
        {
            this.Text = "Click here";
            textBoxState = ComboBoxState.Normal;
            isActivated = false;
        }

        // Redraw the control.
        Invalidate();
    }
}

' Draw the combo box in the current state.
Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
    MyBase.OnPaint(e)

    If Not ComboBoxRenderer.IsSupported Then
        Me.Parent.Text = "Visual Styles	Disabled"
        Return
    End If

    Me.Parent.Text = "CustomComboBox Enabled"

    ' Always draw the main text box and drop down arrow in their 
    ' current states.
    ComboBoxRenderer.DrawTextBox(e.Graphics, topTextBoxRectangle, _
        Me.Text, Me.Font, textBoxState)
    ComboBoxRenderer.DrawDropDownButton(e.Graphics, arrowRectangle, _
        arrowState)

    ' Only draw the bottom text box if the arrow has been clicked.
    If isActivated Then
        ComboBoxRenderer.DrawTextBox(e.Graphics, _
            bottomTextBoxRectangle, bottomText, Me.Font, textBoxState)
    End If
End Sub

Protected Overrides Sub OnMouseDown(ByVal e As MouseEventArgs)
    MyBase.OnMouseDown(e)

    ' Check whether the user clicked the arrow.
    If arrowRectangle.Contains(e.Location) And _
        ComboBoxRenderer.IsSupported Then

        ' Draw the arrow in the pressed state.
        arrowState = ComboBoxState.Pressed

        ' The user has activated the combo box.
        If Not isActivated Then
            Me.Text = "Clicked!"
            textBoxState = ComboBoxState.Pressed
            isActivated = True

        ' The user has deactivated the combo box.
        Else
            Me.Text = "Click here"
            textBoxState = ComboBoxState.Normal
            isActivated = False
        End If

        ' Redraw the control.
        Invalidate()
    End If
End Sub

注解

在调用此方法之前，应验证 属性是否 IsSupported 返回 true。