Introduction to P4 classes, objects, class members

The content of this sectionA class is a model that shows things in the world.

A plane in reality ========================>>> abstract as a class in the program world

class-to-object relationships

1. An object is also called an instance, and is a matter of memory in which the class is instantiated
   • Some classes cannot be instantiated, such as math, we can't say a math
2. According to the class, we can create objects >>> this is the instantiation of
   • The real world is often called objects, the program world is often called instances, the two are not very different, often mixed, not too tangled.
3. Creating an object using the new operator

14:15 started writing programs >>> then we wrote the program ourselves to create an instance.

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows.Forms;namespacedemo2{classProgram {Static voidMain (string[] args) {Form MyForm=NewForm ();        Myform.showdialog (); }    }}

4. Relation of reference variables to instances

Form myForm (reference variable) = new form () (instance);

The reference variable is equivalent to a child, and the instance is a balloon. Image analogy: A child holding a balloon.

* If the balloon does not hold, it will fly away and the instance will be released by garbage collection.

Let's look at another example:

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows.Forms;namespacedemo2{classProgram {Static voidMain (string[] args)            {Form MyForm1;            Form MyForm2; MyForm1=NewForm (); MyForm2=MyForm1;        Myform2.showdialog (); }    }}

This is the equivalent of two children holding a balloon at the same time.

There are three common cases.

1. A child holding a balloon.

2. A child did not hold a balloon.

3. Many children hold a balloon at the same time.

Three members of a class

1. Attribute (property)

* Store data, grouped together to represent the current state of a class or object.
2. Methods (method)

* Evolved from the C language (function) to indicate what the class can do.

* 90% of the time at work is in dealing with methods because he is a member of a class that really does things and makes up logic.

3. event!!! Use

* The mechanism for classes or objects to notify other classes or objects is unique to C #.

* The use of the incident mechanism is very important.

**F1 key to open the MSDN documentation

Some special classes or objects do not focus on members

1. The model class or object is heavy on the property: Entity,framework.

2. Tool class focus on method: Math,console.

3. Notifies the class or object that the event is heavy: time.

42 minutes to write a database

50:36 writing WPF for Time

Now let's do it ourselves and write a time example.

The code is as follows:

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows;usingSystem.Windows.Controls;usingSystem.Windows.Data;usingSystem.Windows.Documents;usingSystem.Windows.Input;usingSystem.Windows.Media;usingSystem.Windows.Media.Imaging;usingSystem.Windows.Navigation;usingSystem.Windows.Shapes;usingSystem.Windows.Threading;namespacewpftime{/// <summary>    ///the interactive logic of MainWindow.xaml/// </summary>     Public Partial classMainwindow:window { PublicMainWindow () {InitializeComponent (); DispatcherTimer Time=NewDispatcherTimer (); Time. Interval= Timespan.fromseconds (1); Time. Tick+=Time_tick; Time.        Start (); }        Private voidTime_tick (Objectsender, EventArgs e) {             This. Timetextbox.text =DateTime.Now.ToString (); //throw new NotImplementedException ();        }    }}

The interface code is as follows:

<Windowx:class= "Wpftime.mainwindow"xmlns= "Http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x= "Http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d= "http://schemas.microsoft.com/expression/blend/2008"XMLNS:MC= "http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local= "Clr-namespace:wpftime"mc:ignorable= "D"Title= "MainWindow"Height= "The "Width= "$">    <Grid>        <TextBoxHorizontalAlignment= "Left"Height= "139"Margin= "10,10,0,0"textwrapping= "Wrap"Name= "Timetextbox"VerticalAlignment= "Top"Width= "774"FontSize= "$"/>    </Grid></Window>

Static members and instance members

* Static member semantically indicates that it is a member of the class >>> is innate and does not need to be instantiated

* Instance (non-static) Chen semantically indicates that it is an "object member."

* Binding refers to how the compiler associates a member with a class or object.

* * not to be underestimated. (decimal) operator

59:02 began to write an example

static method Examples:

usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;usingSystem.Threading.Tasks;usingSystem.Windows.Forms;namespacedemo2{classProgram {Static voidMain (string[] args) {Console.WriteLine ("Hello world!"); }    }}

This lesson concludes.

Introduction to P4 classes, objects, class members