Csharp/CSharp Tutorial/GUI Windows Forms/event
Содержание
- 1 A .NET-compatible event
- 2 Event and event handler
- 3 Events
- 4 Events: add and remove functions
- 5 Events: add and remove functions for a private delegate event
- 6 Events add and remove with synchronized block
- 7 Events and form controls
- 8 Events: Custom Add and Remove with Global delegate cache.
- 9 Fire event in property setter
- 10 Ignored Parameters Anonymous Methods for Button click, kepressed and mouse clicked action
- 11 Use an anonymous method as an event handler
- 12 Use delegate to handle events
- 13 Use the built-in EventHandler delegate
- 14 Using Event Accessors
A .NET-compatible event
<source lang="csharp">using System;
// Derive a class from EventArgs. class MyEventArgs : EventArgs {
public int eventnum;
}
// Declare a delegate for an event. delegate void MyEventHandler(object source, MyEventArgs arg);
// Declare an event class. class MyEvent {
static int count = 0;
public event MyEventHandler SomeEvent;
// This fires SomeEvent.
public void OnSomeEvent() {
MyEventArgs arg = new MyEventArgs();
if(SomeEvent != null) {
arg.eventnum = count++;
Console.WriteLine("Event fired");
SomeEvent(this, arg);
}
}
}
class X {
public void handler(object source, MyEventArgs arg) {
Console.WriteLine("Event " + arg.eventnum + " received by an X object.");
Console.WriteLine("Source is " + source);
Console.WriteLine();
}
}
class Y {
public void handler(object source, MyEventArgs arg) {
Console.WriteLine("Event " + arg.eventnum + " received by a Y object.");
Console.WriteLine("Source is " + source);
Console.WriteLine();
}
}
class MainClass {
public static void Main() {
X ob1 = new X();
Y ob2 = new Y();
MyEvent evt = new MyEvent();
// Add handler() to the event list.
evt.SomeEvent += ob1.handler;
evt.SomeEvent += ob2.handler;
// Fire the event.
evt.OnSomeEvent();
evt.OnSomeEvent();
}
}</source>
Event fired Event 0 received by an X object. Source is MyEvent Event 0 received by a Y object. Source is MyEvent Event fired Event 1 received by an X object. Source is MyEvent Event 1 received by a Y object. Source is MyEvent
Event and event handler
<source lang="csharp">using System; using System.Collections.Generic; using System.Reflection; using System.Runtime.InteropServices; class MyClass : IDisposable {
public event EventHandler OnInitialized;
public event EventHandler OnDisposed;
public void Init()
{
// Initialize our state...
EventHandler onInit = OnInitialized;
if (onInit != null)
onInit(this, new EventArgs());
}
public void Dispose()
{
// Release our state...
EventHandler onDisp = OnDisposed;
if (onDisp != null)
onDisp(this, new EventArgs());
}
} public class MainClass {
public static void Main(){
using (MyClass f = new MyClass())
{
f.OnInitialized += delegate { Console.WriteLine("init"); };
f.OnDisposed += delegate { Console.WriteLine("disposed"); };
f.Init();
}
}
}</source>
init disposed
Events
- Event handlers are represented by delegates.
- Events are members of a class
- Events are declared using the event keyword.
Its most commonly used form is shown here:
<source lang="csharp">event event-delegate object;</source>
- event-delegate is the name of the delegate used to support the event.
- object is the name of the specific event object being created.
Events: add and remove functions
<source lang="csharp">using System; public class Button {
public delegate void ClickHandler(object sender, EventArgs e);
public event ClickHandler Click;
protected void OnClick()
{
if (Click != null)
Click(this, null);
}
public void DoClick()
{
OnClick();
}
} class MainClass {
static public void ButtonHandler(object sender, EventArgs e)
{
Console.WriteLine("Button clicked");
}
public static void Main()
{
Button button = new Button();
button.Click += new Button.ClickHandler(ButtonHandler);
button.DoClick();
button.Click -= new Button.ClickHandler(ButtonHandler);
button.DoClick();
}
}</source>
Button clicked
Events: add and remove functions for a private delegate event
<source lang="csharp">using System; public class Button {
public delegate void ClickHandler(object sender, EventArgs e);
private ClickHandler click;
public void AddClick(ClickHandler clickHandler)
{
click += clickHandler;
}
public void RemoveClick(ClickHandler clickHandler)
{
click -= clickHandler;
}
protected void OnClick()
{
if (click != null)
click(this, null);
}
public void DoClick()
{
OnClick();
}
} class MainClass {
static public void ButtonHandler(object sender, EventArgs e)
{
Console.WriteLine("Button clicked");
}
public static void Main()
{
Button button = new Button();
button.AddClick(new Button.ClickHandler(ButtonHandler));
button.DoClick();
button.RemoveClick(new Button.ClickHandler(ButtonHandler));
button.DoClick();
}
}</source>
Button clicked
Events add and remove with synchronized block
<source lang="csharp">using System; using System.Collections; using System.Runtime.rupilerServices; public class Button {
public delegate void ClickHandler(object sender, EventArgs e);
Hashtable delegateStore = new Hashtable();
static object clickEventKey = new object();
public event ClickHandler Click
{
[MethodImpl(MethodImplOptions.Synchronized)]
add
{
delegateStore[clickEventKey] =
Delegate.rubine((Delegate) delegateStore[clickEventKey],
value);
}
[MethodImpl(MethodImplOptions.Synchronized)]
remove
{
delegateStore[clickEventKey] =
Delegate.Remove((Delegate) delegateStore[clickEventKey],
value);
}
}
protected void OnClick()
{
ClickHandler ch = (ClickHandler) delegateStore[clickEventKey];
if (ch != null)
ch(this, null);
}
public void DoClick()
{
OnClick();
}
} class MainClass {
static public void ButtonHandler(object sender, EventArgs e)
{
Console.WriteLine("Button clicked");
}
public static void Main()
{
Button button = new Button();
button.Click += new Button.ClickHandler(ButtonHandler);
button.DoClick();
button.Click -= new Button.ClickHandler(ButtonHandler);
button.DoClick();
}
}</source>
Button clicked
Events and form controls
<source lang="csharp">using System; using System.Collections.Generic; using System.ruponentModel; using System.Data; using System.Drawing.Drawing2D; using System.Linq; using System.Text; using System.Windows.Forms;
public class Events : Form
{
public Events()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("I have been Clicked");
}
private void textBox1_MouseEnter(object sender, EventArgs e)
{
label1.Text = "Mouse Enters into the TextBox";
}
private void textBox1_MouseLeave(object sender, EventArgs e)
{
label1.Text = "Mouse Leaves the TextBox";
}
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.Alt == true)
label1.Text="The ALT has been pressed";
else
if (e.Control==true)
label1.Text="The Ctrl has been pressed";
else
if (e.Shift==true)
label1.Text="The Shift has been pressed";
}
private void textBox1_KeyUp(object sender, KeyEventArgs e)
{
if (e.Alt == false || e.Control==false || e.Shift==false)
label1.Text = "The Key has been released";
}
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (char.IsDigit(e.KeyChar)==true)
label1.Text = "You have pressed a Numeric key";
else
if(char.IsLetter(e.KeyChar)==true)
label1.Text = "You have pressed a Letter key";
}
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.textBox1 = new System.Windows.Forms.TextBox();
this.label1 = new System.Windows.Forms.Label();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(94, 23);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(75, 23);
this.button1.TabIndex = 0;
this.button1.Text = "Click Me";
this.button1.UseVisualStyleBackColor = true;
this.button1.Click += new System.EventHandler(this.button1_Click);
//
// textBox1
//
this.textBox1.Location = new System.Drawing.Point(81, 78);
this.textBox1.Multiline = true;
this.textBox1.Name = "textBox1";
this.textBox1.Size = new System.Drawing.Size(103, 70);
this.textBox1.TabIndex = 1;
this.textBox1.MouseLeave += new System.EventHandler(this.textBox1_MouseLeave);
this.textBox1.KeyDown += new System.Windows.Forms.KeyEventHandler(this.textBox1_KeyDown);
this.textBox1.KeyUp += new System.Windows.Forms.KeyEventHandler(this.textBox1_KeyUp);
this.textBox1.KeyPress += new System.Windows.Forms.KeyPressEventHandler(this.textBox1_KeyPress);
this.textBox1.MouseEnter += new System.EventHandler(this.textBox1_MouseEnter);
//
// label1
//
this.label1.Font = new System.Drawing.Font("Microsoft Sans Serif", 12F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
this.label1.Location = new System.Drawing.Point(12, 169);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(268, 23);
this.label1.TabIndex = 2;
this.label1.Text = "label1";
this.label1.TextAlign = System.Drawing.ContentAlignment.MiddleCenter;
//
// Events
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(292, 273);
this.Controls.Add(this.label1);
this.Controls.Add(this.textBox1);
this.Controls.Add(this.button1);
this.Name = "Events";
this.Text = "Events";
this.ResumeLayout(false);
this.PerformLayout();
}
private System.Windows.Forms.Button button1;
private System.Windows.Forms.TextBox textBox1;
private System.Windows.Forms.Label label1;
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Events());
}
}</source>
Events: Custom Add and Remove with Global delegate cache.
<source lang="csharp">// copyright 2000 Eric Gunnerson // From A Programmer"s Introduction to C# 2.0, Third Edition using System; using System.Collections; using System.Runtime.rupilerServices; // // Global delegate cache. Uses a two-level hashtable. The delegateStore hashtable // stores a hashtable keyed on the object instance, and the instance hashtable is // keyed on the unique key. This allows fast tear-down of the object when it"s destroyed. // public class DelegateCache {
private DelegateCache() {} // nobody can create one of these
Hashtable delegateStore = new Hashtable(); // top level hash table
static DelegateCache dc = new DelegateCache(); // our single instance
Hashtable GetInstanceHash(object instance)
{
Hashtable instanceHash = (Hashtable) delegateStore[instance];
if (instanceHash == null)
{
instanceHash = new Hashtable();
delegateStore[instance] = instanceHash;
}
return(instanceHash);
}
public static void Combine(Delegate myDelegate, object instance, object key)
{
lock(instance)
{
Hashtable instanceHash = dc.GetInstanceHash(instance);
instanceHash[key] = Delegate.rubine((Delegate) instanceHash[key],
myDelegate);
}
}
public static void Remove(Delegate myDelegate, object instance, object key)
{
lock(instance)
{
Hashtable instanceHash = dc.GetInstanceHash(instance);
instanceHash[key] = Delegate.Remove((Delegate) instanceHash[key],
myDelegate);
}
}
public static Delegate Fetch(object instance, object key)
{
Hashtable instanceHash = dc.GetInstanceHash(instance);
return((Delegate) instanceHash[key]);
}
public static void ClearDelegates(object instance)
{
dc.delegateStore.Remove(instance);
}
} public class Button {
public void TearDown()
{
DelegateCache.ClearDelegates(this);
}
public delegate void ClickHandler(object sender, EventArgs e);
static object clickEventKey = new object();
public event ClickHandler Click
{
add
{
DelegateCache.rubine(value, this, clickEventKey);
}
remove
{
DelegateCache.Remove(value, this, clickEventKey);
}
}
protected void OnClick()
{
ClickHandler ch = (ClickHandler) DelegateCache.Fetch(this, clickEventKey);
if (ch != null)
ch(this, null);
}
public void SimulateClick()
{
OnClick();
}
} class Test {
static public void ButtonHandler(object sender, EventArgs e)
{
Console.WriteLine("Button clicked");
}
public static void Main()
{
Button button = new Button();
button.Click += new Button.ClickHandler(ButtonHandler);
button.SimulateClick();
button.Click -= new Button.ClickHandler(ButtonHandler);
button.TearDown();
}
}</source>
Button clicked
Fire event in property setter
<source lang="csharp">using System; public class SalaryEvent : EventArgs {
public string Message;
public SalaryEvent(string message)
{
this.Message = message;
}
} public class Employee {
private int salary;
public delegate void SalaryTaxEventHandler( object reactor, SalaryEvent myEvent );
public event SalaryTaxEventHandler OnTax;
public int Salary
{
set
{
salary = value;
if (salary > 1000)
{
SalaryEvent myEvent = new SalaryEvent("Employee meltdown in progress!");
OnTax(this, myEvent);
}
}
}
} public class EmployeeMonitor {
public EmployeeMonitor(Employee myEmployee)
{
myEmployee.OnTax += new Employee.SalaryTaxEventHandler(DisplayMessage);
}
public void DisplayMessage( object myEmployee, SalaryEvent myEvent )
{
Console.WriteLine(myEvent.Message);
}
}
class MainClass {
public static void Main()
{
Employee myEmployee = new Employee();
EmployeeMonitor myEmployeeMonitor = new EmployeeMonitor(myEmployee);
myEmployee.Salary = 100;
myEmployee.Salary = 500;
myEmployee.Salary = 2000;
}
}</source>
Employee meltdown in progress!
Ignored Parameters Anonymous Methods for Button click, kepressed and mouse clicked action
<source lang="csharp">using System; using System.Windows.Forms; using System.ruponentModel;
class MainClass
{
static void Main()
{
Button button = new Button();
button.Text = "Click me";
button.Click += delegate { Console.WriteLine("LogPlain"); };
button.KeyPress += delegate { Console.WriteLine("LogKey"); };
button.MouseClick += delegate { Console.WriteLine("LogMouse"); };
Form form = new Form();
form.AutoSize = true;
form.Controls.Add(button);
Application.Run(form);
}
}</source>
Use an anonymous method as an event handler
<source lang="csharp">using System;
delegate void MyEventHandler();
class MyEvent {
public event MyEventHandler SomeEvent;
public void OnSomeEvent() {
if(SomeEvent != null)
SomeEvent();
}
}
class MainClass {
public static void Main() {
MyEvent evt = new MyEvent();
// Use an anonymous method as an event handler.
evt.SomeEvent += delegate {
// This is the event handler.
Console.WriteLine("Event received.");
};
evt.OnSomeEvent();
evt.OnSomeEvent();
}
}</source>
Event received. Event received.
Use delegate to handle events
<source lang="csharp">using System; public class Button {
public delegate void ClickHandler(object sender, EventArgs e);
public ClickHandler Click;
protected void OnClick()
{
if (Click != null)
Click(this, null);
}
public void DoClick()
{
OnClick();
}
} class MainClass {
static public void ButtonHandler(object sender, EventArgs e)
{
Console.WriteLine("Button clicked");
}
public static void Main()
{
Button button = new Button();
button.Click = new Button.ClickHandler(ButtonHandler);
button.DoClick();
}
}</source>
Button clicked
Use the built-in EventHandler delegate
<source lang="csharp">using System;
// Declare an event class. class MyEvent {
public event EventHandler SomeEvent; // uses EventHandler delegate
// This is called to fire SomeEvent.
public void OnSomeEvent() {
if(SomeEvent != null)
SomeEvent(this, EventArgs.Empty);
}
}
class MainClass {
static void handler(object source, EventArgs arg) {
Console.WriteLine("Event occurred");
Console.WriteLine("Source is " + source);
}
public static void Main() {
MyEvent evt = new MyEvent();
// Add handler() to the event list.
evt.SomeEvent += handler;
// Fire the event.
evt.OnSomeEvent();
}
}</source>
Event occurred Source is MyEvent
Using Event Accessors
- You can use event accessors to take control of the event handler list.
- The accessors specify how the event handler list is implemented.
This form is shown here:
<source lang="csharp">event event-delegate event-name {
add {
// code to add an event to the chain
}
remove {
// code to remove an event from the chain
}
}</source>
