C# 列表选择控件之ComboBox

    ComboBox是文本框和列表框的组合，使用更为灵活也更常用

    1.下拉样式

    DropDownStyle属性是最重要的一个属性，用于指定控件的样式。

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
            SetComboBoxDropDownStyle();
        }

        private void addItems()
        {
            this.comboBox1.Items.Add("Item1");
            this.comboBox1.Items.Add("Item2");
            this.comboBox1.Items.Add("Item3");
        }
    }

    常见的样式有

    Simple 用户只能输入文本，不能进行下拉列表选择

        private void SetComboBoxDropDownStyle()
        {
            //设置下拉样式为单纯文本框
            this.comboBox1.DropDownStyle = ComboBoxStyle.Simple;
        }

    DropDownList 用户只能使用下拉列表进行选择

private void SetComboBoxDropDownStyle()
        {
            //设置下拉样式为只能列表选择
            this.comboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
        }

    DropDown 用户就可以文本输入也可以列表选择，综合了上面两种情况

private void SetComboBoxDropDownStyle()
        {
            //设置下拉样式为文本和列表结合
          this.comboBox1.DropDownStyle = ComboBoxStyle.DropDown;
        }

2.重要属性

    2.1 DroppedDown 指示在程序运行中是否显示下拉列表

private void SetComboBoxDropDownStyle()
        {
            //设置下拉样式
            this.comboBox1.DropDownStyle = ComboBoxStyle.DropDown;//这里要显示指定
            this.comboBox1.DroppedDown = true;
        }

    2.2 DropDownHeight 指示下拉列表的高度，当对下拉列表高度大于各项的高度总和时候进行trim

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
            SetDroppedDownHeight();
        }

        private void addItems()
        {
            this.comboBox1.Items.Add("Item1");
            this.comboBox1.Items.Add("Item2");
            this.comboBox1.Items.Add("Item3");
        }

        private void SetDroppedDownHeight()
        {
            this.comboBox1.DropDownHeight = 200;//设置下拉高度
        }
    }

    2.3 DropDownWidth 指示控件宽度，默认控件宽度和下拉宽度相等

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
            SetDroppedDownWidth();
        }

        private void addItems()
        {
            this.comboBox1.Items.Add("Item1");
            this.comboBox1.Items.Add("Item2");
            this.comboBox1.Items.Add("Item3");
        }

        private void SetDroppedDownWidth()
        {
            this.comboBox1.DropDownWidth = 200;//设置下拉高度
        }
    }

    2.4 MaxDropDwnItems 指示下拉列表的可显示的最大项数量.当2.2和2.4冲突的时候，以2.4属性为准

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
            SetMaxDropDownItems();
        }

        private void addItems()
        {
            this.comboBox1.Items.Add("Item1");
            this.comboBox1.Items.Add("Item2");
            this.comboBox1.Items.Add("Item3");
        }

        private void SetMaxDropDownItems()
        {
            this.comboBox1.MaxDropDownItems = 2;//最大显示2项
        }
    }

3.自动补齐(也适合TextBox)

    AutoCompleteCustomSource 进行匹配的数据源之一，和Items类似

    AutoCompleteSource 是一个枚举值表示用什么数据源进行补全

    AutoCompleteMode表示补全时候数据出现的方式

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
            SetAutoCompleteCustomSource();
        }

        private void addItems()
        {
            this.comboBox1.Items.Add("Item1");
            this.comboBox1.Items.Add("Item2");
            this.comboBox1.Items.Add("Item3");
        }

        private void SetAutoCompleteCustomSource()
        {
            this.comboBox1.AutoCompleteCustomSource.
                AddRange(new string[]{"CustomItem1","CustomItem2",
                    "CustomItem3","CustomItem4","CustomItem5",
                    "CustomItem6"});
            this.comboBox1.AutoCompleteSource = AutoCompleteSource.ListItems; //按照下拉列表进行补全
            this.comboBox1.AutoCompleteMode = AutoCompleteMode.Suggest;//只是建议不自动补全
        }

    对于二枚举值有FileSystem,将文件系统作为数据源补全

    FileSystemDirectories，将文件系统中目录作为数据源

    RecentlyUsedList 近期访问的URL补全

    HistoryList，AllUrl,AllSystemSources

    CustomSource则将上面第一个属性作为数据源

    对于三，还有SuggestAppend自动补全且提示，Append自动补全

4.事件

    4.1 DropDown 当展开下拉列表的时候触发

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
        }

        private void addItems()
        {
            this.comboBox1.Items.Add("Item1");
            this.comboBox1.Items.Add("Item2");
            this.comboBox1.Items.Add("Item3");
        }

        private void comboBox1_DropDown(object sender, EventArgs e)
        {
            MessageBox.Show("DropDown事件被触发");
        }

        private void comboBox1_DropDownClosed(object sender, EventArgs e)
        {
            MessageBox.Show("DropDownClosed事件被触发");
        }
    }

        在Designer.cs中InitializeComponent方法中加上

this.comboBox1.DropDown+=new System.EventHandler(this.comboBox1_DropDown);
this.comboBox1.DropDownClosed+=new System.EventHandler(this.comboBox1_DropDownClosed);

        展开列表的时候

        关闭列表的时候

    4.2 SelectedIndexChanged事件，当选中某一项的时候触发

private void InitializeComponent()
        {
            this.comboBox1 = new System.Windows.Forms.ComboBox();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.SuspendLayout();
            // 
            // comboBox1
            // 
            this.comboBox1.FormattingEnabled = true;
            this.comboBox1.Location = new System.Drawing.Point(14, 50);
            this.comboBox1.MaxDropDownItems = 5;
            this.comboBox1.Name = "comboBox1";
            this.comboBox1.Size = new System.Drawing.Size(100, 20);
            this.comboBox1.TabIndex = 0;
            this.comboBox1.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList;
            this.comboBox1.SelectedIndexChanged += new System.EventHandler(this.comboBox1_SelectedIndexChanged);
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(15, 14);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(97, 21);
            this.textBox1.TabIndex = 1;
            // 
            // ComboBox
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(292, 266);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.comboBox1);
            this.Name = "ComboBox";
            this.Text = "ComboBox";
            this.ResumeLayout(false);
            this.PerformLayout();
        }

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
        }

        private void addItems()
        {
            for (int i = 0; i < 100;i++ )
            {
                for (int j = 0; j < i; j++)
                {
                    this.comboBox1.Items.Add("item" + j.ToString());
                }
            }
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            System.Windows.Forms.ComboBox comboBox = (System.Windows.Forms.ComboBox)sender;
            string selectedItem = (string)comboBox.SelectedItem;
            int count = 0;
            int resultIndex = -1;
            resultIndex = comboBox.FindStringExact(selectedItem); //和listbox一样的方法
            while (resultIndex!=-1)
            {
                comboBox.Items.RemoveAt(resultIndex);//删除
                count += 1;
                resultIndex = comboBox.FindStringExact(selectedItem, resultIndex);
            }
            this.textBox1.Text = selectedItem + " 共有" + count + "个";
        }
    }

选中item7之后的结果

    4.3 DrawItem事件，当进行绘制项的时候触发.

    4.4 MeasureItem事件，当描述DrawItem控件中的可选项的时候触发,比如高度变化

public partial class ComboBox : Form
    {
        public ComboBox()
        {
            InitializeComponent();
            addItems();
        }
        private string[] colors;
        private void addItems()
        {
            colors = new string[] { "红", "黄", "蓝" };
            for (int i = 0; i < colors.Length;i++ )
            {
                this.comboBox1.Items.Add(colors[i]);
            }
        }

        private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
        {
            float size = 0;
            System.Drawing.Font font;
            FontFamily family = null;
            System.Drawing.Color color = new System.Drawing.Color();
            switch (e.Index) //正在描绘第几项
            {
                case 0:
                    size = 35;
                    color = System.Drawing.Color.Red;
                    family = FontFamily.GenericMonospace;
                    break;
                case 1:
                    size = 25;
                    color = System.Drawing.Color.Yellow;
                    family = FontFamily.GenericMonospace;
                    break;
                case 2:
                    size = 15;
                    color = System.Drawing.Color.Blue;
                    family = FontFamily.GenericMonospace;
                    break;
            }
            e.DrawBackground();//绘制背景
            Rectangle rectangle = new Rectangle(0, e.Bounds.Top, e.Bounds.Height, e.Bounds.Height);//这里e.Bounds.Height由MeasureItem事件提供
            e.Graphics.FillRectangle(new SolidBrush(color), rectangle);//绘制左边矩形
            //绘制下拉框字体
            font = new Font(family, size, FontStyle.Regular);//正常的字体样式
            e.Graphics.DrawString(colors[e.Index], font, System.Drawing.Brushes.Black,
                new RectangleF(e.Bounds.X+rectangle.Width,e.Bounds.Y,e.Bounds.Width,e.Bounds.Height));//绘制文字,这里width由MeasureItem提供
            e.DrawFocusRectangle();//绘制各子项*
        }

        private void comboBox1_MeasureItem(object sender, MeasureItemEventArgs e)
        {
            switch (e.Index)
            {
                case 0:
                    e.ItemHeight = 40;
                    break;
                case 1:
                    e.ItemHeight = 30;
                    break;
                case 2:
                    e.ItemHeight = 20;
                    break;
            }
            e.ItemWidth=100;
        }
    }

private void InitializeComponent()
        {
            this.comboBox1 = new System.Windows.Forms.ComboBox();
            this.SuspendLayout();
            // 
            // comboBox1
            // 
            this.comboBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawVariable;
            this.comboBox1.DropDownHeight = 300;
            this.comboBox1.FormattingEnabled = true;
            this.comboBox1.IntegralHeight = false;
            this.comboBox1.Location = new System.Drawing.Point(10, 20);
            this.comboBox1.MaxDropDownItems = 5;//最多展示5个
            this.comboBox1.Name = "comboBox1";
            this.comboBox1.Size = new System.Drawing.Size(140, 22);
            this.comboBox1.TabIndex = 0;
            this.comboBox1.DrawItem += new System.Windows.Forms.DrawItemEventHandler(this.comboBox1_DrawItem);//注册两个事件
            this.comboBox1.MeasureItem += new System.Windows.Forms.MeasureItemEventHandler(this.comboBox1_MeasureItem);
            // 
            // ComboBox
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(292, 266);
            this.Controls.Add(this.comboBox1);
            this.Name = "ComboBox";
            this.Text = "ComboBox";
            this.ResumeLayout(false);

        }