Events Where are we? Stamp Tool Catch Me If You Can Weve Gotten - - PowerPoint PPT Presentation

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Events Where are we? Stamp Tool Catch Me If You Can Weve Gotten - - PowerPoint PPT Presentation

Nov 24, 2022 160 likes •539 views

Events Where are we? Stamp Tool Catch Me If You Can Weve Gotten Ahead of Ourselves Source: The Hobbit Start at the Beginning Source: The Hobbit Learning Goals 1. Write a program that can respond to mouse events 2. Use an instance

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Events

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Where are we?

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Stamp Tool

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Catch Me If You Can

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Source: The Hobbit

We’ve Gotten Ahead of Ourselves

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Source: The Hobbit

Start at the Beginning

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Learning Goals

1. Write a program that can respond to mouse events

  • 2. Use an instance variable in your program
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  • When users interact with computer they generate

events (e.g., moving/clicking the mouse)

  • Can respond to events by having listener for events

addMouseListeners()

  • Listeners get control of the program when an event

happens.

Using portions of slides by Eric Roberts

Listener Model

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mouseClicked(e) mousePressed(e) mouseReleased(e) mouseMoved(e) mouseDragged(e) Called when the user clicks the mouse Called when the mouse button is pressed Called when the mouse button is released Called when the user moves the mouse Called when the mouse is dragged with the button down

The parameter e is MouseEvent object, which provides more data about event, such as the location of mouse.

  • 1. The run method should call addMouseListeners
  • 2. Write definitions of any listener methods needed

Using portions of slides by Eric Roberts

Responding to Mouse Events

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Hole Puncher

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Now With Dancing Children

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Normal Program

Run Method

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New Listener Characters

Mouse Clicked Method Mouse Listener

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Program Starts Running

Run Method Mouse Clicked Method

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Add Mouse Listener

Run Method Mouse Listener Mouse Clicked Method addMouseListeners();

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Program Runs as Usual

Run Method Mouse Listener Mouse Clicked Method

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Mouse Clicked!

Run Method Mouse Listener Mouse Clicked Method

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Calls Mouse Clicked Method

Run Method Mouse Listener Mouse Clicked Method

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Run Method Mouse Listener Mouse Clicked Method

When done, Run continues.

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Run Method Mouse Listener Mouse Clicked Method

Keeps Doing Its Thing…

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Mouse Moved!

Run Method Mouse Listener Mouse Clicked Method

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Calls Mouse Clicked Method

Run Method Mouse Listener Mouse Clicked Method

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When done, Run continues.

Run Method Mouse Listener Mouse Clicked Method

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Mouse Tracker

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  • 1. Variables exist until their inner-most code block ends.
  • 2. If a variable is defined outside all methods, its inner-most

code block is the entire program!

  • 3. We call these variables instance variables

Instance Variables

* Instance variables have special meanings in programs with multiple files. For now you need to know that all methods can see them and that their initialization line is executed before run.

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Often you need instance variables to pass information between the run method and the mouse event methods!

Instance Variables + Events

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Objects have a special value called null which means this variable is not associated with a value yet.

Null

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Debris Sweeper

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getElementAt(x, y);

  • getElementAt(x, y) will return any

GObject at the (x, y) coordinates. It will return null if there is no object at those coordinates.

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And Here We Are…

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Stamp Tool

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New Commands

  • addMouseListeners();
  • getElementAt(x, y);

New Ideas

  • The Listener Model
  • Instance Variables
  • null

New Concepts

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mouseClicked(e) mousePressed(e) mouseReleased(e) mouseMoved(e) mouseDragged(e) Called when the user clicks the mouse Called when the mouse button is pressed Called when the mouse button is released Called when the user moves the mouse Called when the mouse is dragged with the button down

The parameter e is MouseEvent object, which provides more data about event, such as the location of mouse.

  • 1. The run method should call addMouseListeners
  • 2. Write definitions of any listener methods needed

Using portions of slides by Eric Roberts

Responding to Mouse Events

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keyPressed(e) keyReleased(e) keyTyped(e) Called when the user presses a key Called when the key comes back up Called when the user types (presses and releases) a key

The parameter e is a KeyEvent object, which indicates which key is involved.

  • 1. The run method should call addKeyListeners
  • 2. Write definitions of any listener methods needed

Using portions of slides by Eric Roberts

Responding to Keyboard Events

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Warm Up: Making Tracks

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Catch Me If You Can?