C # skills and analytical (part)

DesignMode

The following items in the designer interface, you need to determine DesignMode

• OnPaint(e)/Form_Paint

Analyzing method requires a special custom controls, as follows:

    public partial class Ctl : Control
    {
        public Ctl()
        {
            InitializeComponent();
        }

        protected override void OnPaint(PaintEventArgs pe)
        {
            base.OnPaint(pe);
            Graphics g = pe.Graphics;
            g.DrawRectangle(new Pen(Brushes.Black, 5), new Rectangle(5, 5, 30, 30));

            if (!this.IsDesignMode())
                g.FillEllipse(Brushes.Red, new Rectangle(5, 5, 30, 30));
        }

        protected virtual bool IsDesignMode()
        {
            // DesignMode 并不能反映当前环境是否是运行时，
            // 它只能告诉你这个控件当前是不是直接被设计器操作（嵌套的已经不算了） 
            bool designMode = false;
#if DEBUG
            designMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime) ||
                 (Process.GetCurrentProcess().ProcessName == "devenv");
#endif
            return designMode;
        }
    }

    

override and new

• The main difference:

  • Method override base class rewriting; new new method in the base class Hide

  • override rewritable virtual override abstract modification method; new new base class virtual methods and ordinary methods can be hidden

  • override can not override a non-virtual and static methods ( Note: static class can not be inherited ), can not use the new static virtual abstract method override modification

  • new keywords with private modification, only hidden in the derived class in the base class methods, other than derived class does not hide base class methods ( prohibiting the use of such a case, meaningless )

• virtual Examples:

    public class Animal
    {
        public void Voice()
        {
            this.OnSound();
        }

        protected virtual void OnSound()
        {
            Console.WriteLine(Const.SOUND);
        }

    }

    public class Tiger:Animal
    {
        
        public void Sound()
        {
            base.OnSound();
        }

        protected override void OnSound()
        {
            //base.OnVoice();
            Console.WriteLine(Const.VOICE);
        }
    }

            Animal animal = new Animal();
            animal.Voice();
            //virtual重写
            Tiger tiger = new Tiger();
            tiger.Sound();
            tiger.Voice();

• abstract example:

    public abstract class Bird
    {
        public abstract void Fly();
    }

    public class Sparrow : Bird
    {
        //继承抽象类，必须实现抽象类的所有方法
        public override void Fly()
        {
            Console.WriteLine(Const.FLY);
        }
    }

            //abstract重写
            Sparrow sparrow = new Sparrow();
            sparrow.Fly();

• override Example:

    public class Sparrow_Black : Sparrow
    {
        public override void Fly()
        {
            Console.WriteLine(Const.BLACK);
            base.Fly();
        }
    }

            //override重写
            Sparrow_Black black= new Sparrow_Black();
            black.Fly();

• new example:

    public class Tiger_White:Tiger
    {
        public new void Sound()
        {
            Console.WriteLine();
        }
    }

            //new
            Tiger_White white = new Tiger_White();
            white.Sound();
            white.Voice();

Optional parameters

• After the optional parameters must be essential parameters

• Optional parameters can not use ref or out modifier

• The default value must be specified as a constant: numeric or string literal, null, const member, enum member and default (T) operator

        public void Move(int speed = 100)
        {
            Console.WriteLine("移动速度：" + speed);
        }

            Animal animal = new Animal();
            animal.Move();
            animal.Move(200);

params variable parameters

params parameter is one-dimensional array, the method must be the last parameter

        public void Foot(params string[] foots)
        {
            StringBuilder sb = new StringBuilder();
            foreach (var foot in foots)
                sb.Append(foot);
            Console.WriteLine(sb.ToString());
        }

            Animal animal = new Animal();
            animal.Foot("前肢");
            animal.Foot("前肢","后肢");
            animal.Foot(new string[] { "前肢", "后肢" });

Nullable type

System.Nullable

            int? no = null;
            Console.WriteLine(no.HasValue);
            Console.WriteLine(no??0);

            no = 1;
            Console.WriteLine(no.HasValue);
            Console.WriteLine(no.Value);

Extension Methods

• Method Statement

  • You must be a non-nested, non-generic static class

  • At least one parameter

  • The first argument must be attached to this keyword as a prefix

  • The first argument can not have any other modifiers

  • The first type is a pointer type parameter can not

  • The extended type (extended type) is called a first parameter method

    public static class Util
    {

        public static bool IsEmpty(this string str)
        {
            if (string.IsNullOrEmpty(str))
                return true;
            str = str.Trim();
            if (string.IsNullOrEmpty(str))
                return true;
            return false;
        }
    }

            string str = null;
            string empty = string.Empty;
            string blank = "   ";

            Console.WriteLine(str.IsEmpty());
            Console.WriteLine(empty.IsEmpty());
            Console.WriteLine(blank.IsEmpty());

Entrusted with the multicast delegate

        public event EventHandler Eat;//事件

        public void OnEat(EventArgs args)
        {
            if (Eat != null)
                Eat(this, args);//触发事件
        }

            animal.Eat += Animal_Eat;//多播委托
            animal.Eat += Animal_Eat;

            animal.OnEat(new EventArgs());

        private static void Animal_Eat(object sender, EventArgs e)
        {
            Console.WriteLine(Const.EAT);
        }