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6.8.1 委任式事件模型(Delegation Event Model)
一個source可以產生和送出Event給一個或多個Listener，每一個Listener總是隨時等待接收event，一旦接收到一個event，Listener就會立即處理它並傳回結果。任何一個使用者介面元件都可以委任這個程序模型來處理事件。
event(事件)：
event是一種用來描述狀態改變的物件。當使用者與GUI介面連續互動時，將會有一系列的event產生。例如按下一個button,從鍵盤輸入一個字元,從一個list
box選擇一個item,或是click一下滑鼠。
event source(事件來源)：
source是一個產生event的物件，它可以產生一種或多種不同的事件，一個Source必須先註冊(register)才能夠委任listener來處理它的事件，每一個event都有它自己的註冊方法(成員函式)，標準型態為：
public void addTypeListener(TypeListener
el)
例如註冊一個鍵盤事件listener的成員函式為：
addKeyListener( )
而註冊一個滑鼠移動事件的listener的成員函式為：
addMouseMotionListener( )
某些source可以允許註冊多種listener，其型態為：
public void
addTypeListener(TypeListener el)
如果想要解除註冊，可以使用
public void
removeTypeListener(TypeListener el)
event source(事件來源)：
一個listener是一個等待被event通知的物件。使用listener有兩個條件，第一listener必須先被註冊才能使用。第二必須定義相關成員函式以便接收和處理事件。所有listener的成員函式都宣告在java.awt.event的package中。
6.8.2 event物件類別
所有Java語言的event物件類別都繼承自EventObject
，包括awt所有GUI元件的event物件類別AWTEvent。
EventObject 有兩個成員函式: getSource( ) 和 toString( ).
java.awt.event
主要的event事件類別
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Event
Class |
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Description |
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ActionEvent |
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Generated when a button is
pressed, a list item is double-clicked, or a menu item is
selected. |
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AdjustmentEvent |
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Generated when a scroll bar
is manipulated. |
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ComponentEvent |
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Generated when a component
is hidden, moved, resized, or becomes visible. |
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ContainerEvent |
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Generated when a component
is added to or removed from a container. |
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FocusEvent |
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Generated when a component
gains or loses keyboard focus. |
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InputEvent |
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Abstract super class for all
component input event classes. |
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ItemEvent |
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Generated when a check box
or list item is clicked; also occurs when a choice selection is made or a
checkable menu item is selected or deselected. |
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KeyEvent |
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Generated when input is
received from the keyboard. |
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MouseEvent |
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Generated when the mouse is
dragged, moved, clicked, pressed, or released; also generated when the mouse
enters or exits a component. |
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TextEvent |
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Generated when the value of
a text area or text field is changed. |
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WindowEvent |
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Generated when a window is
activated, closed, deactivated, deiconified, iconified, opened, or
quit. |
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6.8.3 Sources of Events物件類別
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Event Source |
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Description |
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Button |
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Generates action events when the button
is pressed. |
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Checkbox |
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Generates item events when the check
box is selected or deselected. |
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Choice |
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Generates item events when the choice
is changed. |
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List |
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Generates action events when an item is
double-clicked; generates item events when an item is selected or
deselected. |
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Menu Item |
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Generates action events when a menu
item is selected; generates item events when a checkable menu item is selected
or deselected. |
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Scrollbar |
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Generates adjustment events when the
scroll bar is manipulated. |
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Text components |
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Generates text events when the user
enters a character. |
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Window |
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Generates window events when a window
is activated, closed, deactivated, deiconified, iconified, opened, or
quit. |
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6.8.4 Event Listener物件類別： Interfaces
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Event Listener
Interfaces |
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Interface |
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Description |
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ActionListener |
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Defines one method to receive action
events. |
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AdjustmentListener |
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Defines one method to receive
adjustment events. |
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ComponentListener |
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Defines four methods to recognize when
a component is hidden, moved, resized, or shown. |
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ContainerListener |
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Defines two methods to recognize when a
component is added to or removed from a container. |
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FocusListener |
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Defines two methods to recognize when a
component gains or loses keyboard focus. |
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ItemListener |
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Defines one method to recognize when
the state of an item changes. |
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KeyListener |
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Defines three methods to recognize when
a key is pressed, released, or typed. |
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MouseListener |
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Defines five methods to recognize when
the mouse is clicked, enters a component, exits a component, is pressed, or is
released. |
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MouseMotionListener |
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Defines two methods to recognize when
the mouse is dragged or moved. |
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TextListener |
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Defines one method to recognize when a
text value changes. |
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WindowListener |
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Defines seven methods to recognize when
a window is activated, closed, deactivated, deiconified, iconified, opened, or
quit. |
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6.8.5 滑鼠事件驅動程式設計
為了掌握滑鼠得事件，我們需定義兩個物件類別：
─ MouseListener interfaces
─
MouseMotionListener
interfaces
下列範例程式用來展示滑鼠事件的處理：
// Demonstrate the mouse event handlers.
import java.awt.*;
import
java.awt.event.*;
import java.applet.*;
public class ex9 extends
Applet
implements MouseListener, MouseMotionListener
{
String msg = "";
int mouseX = 0, mouseY = 0; // coordinates of
mouse
public void init()
{
addMouseListener(this);
addMouseMotionListener(this);
}
// Handle mouse
clicked.
public void mouseClicked(MouseEvent me)
{
// save
coordinates
mouseX = 0;
mouseY = 10;
msg = "滑鼠咬我！";
repaint();
}
// Handle mouse entered.
public void
mouseEntered(MouseEvent me)
{
// save coordinates
mouseX =
0;
mouseY = 10;
msg = "滑鼠進來了！";
repaint();
}
// Handle mouse exited.
public void mouseExited(MouseEvent me)
{
// save coordinates
mouseX = 0;
mouseY = 10;
msg = "滑鼠出去了！";
repaint();
}
// Handle button
pressed.
public void mousePressed(MouseEvent me)
{
// save
coordinates
mouseX = me.getX();
mouseY = me.getY();
msg
= "按下";
repaint();
}
// Handle button released.
public void mouseReleased(MouseEvent me)
{
// save coordinates
mouseX = me.getX();
mouseY =
me.getY();
msg = "放開";
repaint();
}
// Handle
mouse dragged.
public void mouseDragged(MouseEvent me)
{
//
save coordinates
mouseX = me.getX();
mouseY = me.getY();
msg = "*";
showStatus("滑鼠現在位置：" + mouseX + ", " + mouseY);
repaint();
}
// Handle mouse moved.
public void
mouseMoved(MouseEvent me)
{
// show status
showStatus("滑鼠現在位置：" + me.getX() + ", " + me.getY());
}
// Display msg in applet window at current X,Y location.
public
void paint(Graphics g)
{
g.drawString(msg, mouseX, mouseY);
}
}
6.8.6 Keyboard事件處理
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class SimpleKey extends Applet implements KeyListener
{
String msg = "";
int X = 10, Y = 20; // output coordinates
public void init()
{
addKeyListener(this);
requestFocus(); // request input focus
}
public void
keyPressed(KeyEvent ke)
{
showStatus("Key按下");
}
public void keyReleased(KeyEvent ke)
{
showStatus("Key放開");
}
public void keyTyped(KeyEvent
ke)
{
msg += ke.getKeyChar();
repaint();
}
// Display keystrokes.
public void paint(Graphics g)
{
g.drawString(msg, X, Y);
}
}
如果想使用一些特殊的功能鍵，如<F1>, <F2>,...,<PgDn>,
<PgUp>...，範例程式如下：
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class KeyEvents extends Applet implements KeyListener
{
String msg = "";
int X = 10, Y = 20; // output coordinates
public void init()
{
addKeyListener(this);
requestFocus(); // request input focus
}
public void
keyPressed(KeyEvent ke)
{
showStatus("Key按下");
int
key = ke.getKeyCode();
switch(key)
{
case
KeyEvent.VK_F1:
msg += "<F1>";
break;
case KeyEvent.VK_F2:
msg += "<F2>";
break;
case KeyEvent.VK_F3:
msg +=
"<F3>";
break;
case KeyEvent.VK_PAGE_DOWN:
msg += "<PgDn>";
break;
case
KeyEvent.VK_PAGE_UP:
msg += "<PgUp>";
break;
case KeyEvent.VK_LEFT:
msg += "<Left Arrow>";
break;
case KeyEvent.VK_RIGHT:
msg +=
"<Right Arrow>";
break;
}
repaint();
}
public void keyReleased(KeyEvent ke)
{
showStatus("Key放開");
}
public void keyTyped(KeyEvent
ke)
{
msg += ke.getKeyChar();
repaint();
}
// Display keystrokes.
public void paint(Graphics g)
{
g.drawString(msg, X, Y);
}
}
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