.NET快速开发实践之应用IExtenderProvider实现控件焦点跳转

我在前面的.NET快速开发实践中的IExtenderProvider扩展组件和其他两篇Post介绍了IExtenderProvider扩展编程模式和应用IExtenderProvider实现实体与对象的做法与例子，下面我为介绍一下在管理信息系统开发中一个常用的功能，控件的输入焦点跳转，我们知道，系统为我们提供了Tab和Shift+Tab切换输入焦点的功能，但是这里面有一个问题，即最终操作者最不习惯于使用Tab进行切换输入焦点，因为都已经习惯于无鼠标操作，常使用回车，上下方向键进行操作以实现焦点切换。

那么我们如何实现这样的功能，最普通的方法是处理输入控件的KeyDown事件，判读按键是否满足跳转：例如

        private void tbName_KeyDown(object sender, KeyEventArgs e)
        {
            if(e.KeyCode == Keys.Enter) //回车向下一焦点跳转
			{
                this.tbInputCode1.Focus();
			}
            else if(e.KeyCode == Keys.Up) //向上键向上一焦点跳转
			{
                this.tbCode.Focus();
        }

这样的做法，我们就必须重写所有输入控件的KeyDown事件，效率低下，也影响代码的美观，我们可以通过应用应用IExtenderProvider实现另一种方式，即把这样的功能封装在一个名字叫ControlFocus的组件中：

    [ToolboxItem(true)]
    [Description("控制焦点跳转组件")]
	[ProvideProperty( "NextControl", typeof(Control)) ]
    [ProvideProperty("PreviousControl", typeof(Control))]
	public class ControlFocus:Component, IExtenderProvider
	{
        Dictionary<Control, Control> _NextFocus = new Dictionary<Control, Control>();
        Dictionary<Control, Control> _PreviousFocus = new Dictionary<Control, Control>();

        private Keys [] nextKeys;
        private Keys[] previousKeys;

		public ControlFocus()
		{
			
		}
        
        public ControlFocus(System.ComponentModel.IContainer container)
        {
            container.Add(this);
        }

        [Category("焦点跳转")]
        [Description("获取/设置向前跳转按键集合")]
        public Keys[] NextKeys
        {
            get
            {
                return this.nextKeys;
            }
            set
            {
                this.nextKeys = value;
            }
        }

        [Category("焦点跳转")]
        [Description("获取/设置向后跳转按键集合")]
        public Keys[] PreviousKeys
        {
            get
            {
                return this.previousKeys;
            }
            set
            {
                this.previousKeys = value;
            }
        }

        [Category("焦点跳转")]
        [Description("获取/设置向前跳转控件")]
        public System.Windows.Forms.Control GetNextControl(Control control)
        {
            if (_NextFocus.ContainsKey(control))
            {
                return _NextFocus[control];
            }
            return null;
        }

        public void SetNextControl(Control control, Control nextControl)
		{
            if (_NextFocus.ContainsKey(control) != true)
			{
				_NextFocus.Add(control,nextControl);
                control.KeyDown += new KeyEventHandler(Control_KeyDown);
			}
			else
			{
				_NextFocus[control] = nextControl;
			}
		}

        [Category("焦点跳转")]
        [Description("获取/设置向后跳转控件")]
        public Control GetPreviousControl(Control control)
        {
            if (_PreviousFocus.ContainsKey(control))
            {
                return (System.Windows.Forms.Control)_PreviousFocus[control];
            }
            return null;
        }

        public void SetPreviousControl(Control control, Control previousControl)
		{
            if (_PreviousFocus.ContainsKey(control) != true)
			{
				_PreviousFocus.Add(control,previousControl);
                control.KeyDown += new KeyEventHandler(Control_KeyDown);
			}
			else
			{
				_PreviousFocus[control] = previousControl;
			}
		}        

		private void Control_KeyDown(object sender, KeyEventArgs e)
		{
			if(NextKeysContains(e.KeyCode))
			{
                          Control nextControl = this.GetNextControl((Control)sender);
				if(nextControl != null && nextControl.CanFocus)
					nextControl.Focus();
			}
            else if (PreviousKeysContains(e.KeyCode))
			{
                           Control previousControl = this.GetPreviousControl((Control)sender);
				if(previousControl != null && previousControl.CanFocus)
					previousControl.Focus();
			}            
		}

        internal bool NextKeysContains(Keys k)
        {
            if (this.nextKeys == null)
                return false;

            for (int i = 0; i < this.nextKeys.Length; i++)
            {
                if (this.nextKeys[i] == k)
                    return true;
            }

            return false;
        }

        internal bool PreviousKeysContains(Keys k)
        {
            if (this.previousKeys == null)
                return false;

            for (int i = 0; i < this.previousKeys.Length; i++)
            {
                if (this.previousKeys[i] == k)
                    return true;
            }

            return false;
        }

        #region IExtenderProvider 成员

        bool IExtenderProvider.CanExtend(object component)
        {
            if (component is Control && !(component is Form))
            {
                return true;
            }

            return false;
        }

        #endregion
    }

下面我们来看看如何应用ControlFocus，拖出一个ControlFocus设置跳转按键值，可以通过属性窗口，也可以通过代码：

        public DiagnosisEditor()
        {
            InitializeComponent();
            
            this.controlFocus1.NextKeys = new Keys[] {Keys.Enter,Keys.PageDown};
            this.controlFocus1.PreviousKeys = new Keys [] {Keys.PageUp};
        }

下面设置输入控件的焦点跳转顺序，需要为每个控件设置下一个焦点控件和前一焦点控件：