c＃：当光标进入或悬停在其上时，按钮显示空白

Question

当光标进入或悬停在此按钮（cmdRefresh）控件上时，它会在工具提示上显示一个空白方块。未为此控件定义鼠标事件，仅定义事件已定义

this.cmdRefresh.AutoEllipsis = true;
this.cmdRefresh.BackColor = System.Drawing.SystemColors.ButtonFace;
this.cmdRefresh.Cursor = System.Windows.Forms.Cursors.Default;
resources.ApplyResources(this.cmdRefresh, "cmdRefresh");
this.cmdRefresh.ForeColor = System.Drawing.SystemColors.ControlText;
this.cmdRefresh.Name = "cmdRefresh";
this.ToolTip1.SetToolTip(this.cmdRefresh, resources.GetString("cmdRefresh.ToolTip"));
this.cmdRefresh.UseVisualStyleBackColor = true;
this.cmdRefresh.Click += new System.EventHandler(this.cmdRefresh_Click);


public void cmdRefresh_Click()
    {
        Cursor.Current = Cursors.Default;
        frmApplication.DefInstance.StatusBar1.Items["Message"].Text = MainModule.g_sReadyMessage;
        if (frmApplication.DefInstance.cmdRefresh.Visible)
        {
            frmApplication.DefInstance.cmdRefresh.Focus();
        }
    }