鼠标滚轮事件

Question

我创建了一个简单的应用程序，用于使用鼠标滚轮在图片框内缩放图像。它在我的开发笔记本电脑（Win10）上完美运行。但是当我在我的台式电脑（Win7）上运行它时，缩放（使用鼠标滚轮）功能不起作用。

下面是我的实现代码片段:

        private void InitializeComponent()
    {
        this.pictureBox1 = new System.Windows.Forms.PictureBox();
        this.panel1 = new System.Windows.Forms.Panel();
        ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
        this.panel1.SuspendLayout();
        this.SuspendLayout();
        // 
        // pictureBox1
        // 
        this.pictureBox1.Location = new System.Drawing.Point(4, 0);
        this.pictureBox1.Margin = new System.Windows.Forms.Padding(4);
        this.pictureBox1.Name = "pictureBox1";
        this.pictureBox1.Size = new System.Drawing.Size(493, 583);
        this.pictureBox1.SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize;
        this.pictureBox1.TabIndex = 0;
        this.pictureBox1.TabStop = false;
        this.pictureBox1.Click += new System.EventHandler(this.pictureBox1_Click);
        this.pictureBox1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.pictureBox1_MouseDown);
        this.pictureBox1.MouseMove += new System.Windows.Forms.MouseEventHandler(this.pictureBox1_MouseMove);
        this.pictureBox1.MouseUp += new System.Windows.Forms.MouseEventHandler(this.pictureBox1_MouseUp);
        this.pictureBox1.MouseWheel += new System.Windows.Forms.MouseEventHandler(this.pictureBox1_MouseWheel);
        // 
        // panel1
        // 
        this.panel1.AutoScroll = true;
        this.panel1.AutoSize = true;
        this.panel1.Controls.Add(this.pictureBox1);
        this.panel1.Location = new System.Drawing.Point(1, 2);
        this.panel1.Name = "panel1";
        this.panel1.Size = new System.Drawing.Size(714, 593);
        this.panel1.TabIndex = 1;
        // 
        // Form1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(8F, 16F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.AutoScroll = true;
        this.ClientSize = new System.Drawing.Size(719, 594);
        this.Controls.Add(this.panel1);
        this.Margin = new System.Windows.Forms.Padding(4);
        this.Name = "Form1";
        this.Text = "Form1";
        this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.Form1_FormClosing);
        ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
        this.panel1.ResumeLayout(false);
        this.panel1.PerformLayout();
        this.ResumeLayout(false);
        this.PerformLayout();

    }

private float ZOOM = 1.5f
private void pictureBox1_MouseWheel(object sender, System.Windows.Forms.MouseEventArgs e)
    {
        pictureBox1.Focus();
        if (e.Delta < 0) //ZoomIn
        {
            Console.WriteLine("Mouse Wheel Zoom In");

            if ((pictureBox1.Width < panel1.Width) && (pictureBox1.Height < panel1.Height))
            {
                pictureBox1.Width = Convert.ToInt32(pictureBox1.Width * ZOOM);
                pictureBox1.Height = Convert.ToInt32(pictureBox1.Height * ZOOM);
                pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;

                this.Refresh();                    
            }

        }
        else
        {
            //ZoomOut
            Console.WriteLine("Mouse Wheel Zoom Out");
            if ((pictureBox1.Width > panel1.Width) &&
            (pictureBox1.Height > panel1.Height))
            {
                pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
                pictureBox1.Width = Convert.ToInt32(pictureBox1.Width / ZOOM);
                pictureBox1.Height = Convert.ToInt32(pictureBox1.Height / ZOOM);
            }
        }
    }

我认为这是由于我的台式电脑的 Control.MouseWheel 事件出现了问题。当我调试时，即使我已经将焦点放在图片框内或单击了它，该事件也从未出现过。当我尝试使用筛选消息 WM_MOUSEWHEEL = 0x20a; 来实现其他方案时，它可以在我的笔记本电脑和台式电脑上都正常工作。有任何想法是为什么会出现这些不同的行为吗？谢谢你的时间。

- fins

---

Win10有一个名为“当我将鼠标悬停在它们上方时滚动非活动窗口”的系统选项，默认情况下已打开。Win7没有这个选项。PictureBox和Panel都不会被视为“活动的”。你可以订阅PictureBox的MouseMove事件并调用其Focus()方法作为解决方法。 - Hans Passant

谢谢@HansPassant。我添加了MouseHover事件，现在它可以工作了。 - fins

Answer 1

原来Win 10有一个系统选项叫做“在鼠标悬停时滚动非活动窗口”。这就是为什么我的先前的代码只能在Win 10上运行的原因。我添加了以下行以修复它。感谢@HansPassant的提示。

    private void picBox_MouseHover(object sender, EventArgs e)
    {
        picBox.Focus();
    }

- fins