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Graphical User Interface (GUI) Programming I

Graphical User Interface (GUI) Programming I. Lecture Objectives. Understand the basic concepts of Graphical User Interfaces (GUIs) Practice Basic GUI Programming in Java Develop Basic GUI Applications Study Layout Management and Managers for GUI Applications. Outline.

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Graphical User Interface (GUI) Programming I

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  1. Graphical User Interface (GUI) Programming I

  2. Lecture Objectives • Understand the basic concepts of Graphical User Interfaces (GUIs) • Practice Basic GUI Programming in Java • Develop Basic GUI Applications • Study Layout Management and Managers for GUI Applications

  3. Outline Graphical User Interfaces (GUIs) -- Overview -- Essential elements Containers -- Overview -- Examples Components -- Overview -- Examples Layout Managers -- Overview -- Examples

  4. Downloading libcrypt ... Enter Edit File 40% Cancel Open Save Save As... Quit Graphical User Interface (GUI) • A Graphical User Interface (GUI) is one variety of user interface. • User interacts with objects on the screen (icons, buttons, scroll-bars, etc.) via mouse clicks or keyboard actions. Ok

  5. GUI Popularity • Popularized in 1980s by the Macintosh. • Now state of the practice, and not final word in UI • Intended to replace text-based "command line" and "function key" interfaces. • Despite similarities, GUIs are typically platform-specific (Windows 95/98/NT/1900, MacOS, X Windows look-and-feel standards). • Some graphical toolkits now provide cross-platform APIs. E.g. wxWindows, GTK+, Java.

  6. 1. 2. Java’s GUI Capabilities Java provides essentially two related toolkits for making GUIs: The Abstract Windowing Toolkit ("AWT"), and The Java Foundation Classes ("Swing") Swing is merely an expanded version of the AWT, and provides greater control and convenience.

  7. Why Two Toolkits in Java? MFC and always "BSoD" AWT, then JFC or "Swing" Well, it’s a long story. In short, JFC (swing) is Sun’s answer to Microsoft’s MFC--a detailed toolkit library.

  8. Button JButton Cautionary Note • Java has two flavors of toolkits: • Swing. • AWT. • It is not wise to mix AWT and Swing Components. For your first programs, stick with one toolkit (swing!!!). • We’ll start off with AWT Components to show the basics. • Then, we will switch to Swing Components. • How do you tell them apart? • Generally, but not always, Swing Components will have a • "J" in front of the class name: AWT Swing

  9. Keep in Mind • We will program graphical elements in source code. • There are drag and drop systems (graphical integrated development environments (IDEs). • Java is designed to work across different platforms. • This poses special challenges!!! • As does the very nature of WIMP GUI’s (windows, icons, menus, and pointing device graphic user interface)

  10. Steps to GUI Construction We will learn GUI creation in two steps: the "view", and then the "controls" or event handling. 1. • In Java, to create a GUI, you (1): • Specify a Container, using . . . • a Layout Manager to . . . • place Components and/or Containers of Components . . . on the screen as desired. i.e. UI form and appearance TODAY LATER 2. • In Java, to make a GUI act as the • interface for a program, you (2) • Design human/computer dialog, using Listeners and component-generated events i.e. UI interaction and behavior

  11. File Edit Help CLICK ME GUI Design & Creation There are three essential constructs in any GUI: Containers -- used to hold items (e.g., the frame) Components -- the widgets or interactors (e.g., buttons) LayoutManagers -- the hidden algorithm used to organize the widgets inside the container offset offset

  12. GUI Basic Constructs 1. Containers File Edit Help offset 2. Components CLICK ME 3. LayoutManagers offset The three basic constructsused in every GUI are:

  13. Examples of Containers: Swing AWT • JPanel • JFrame • JApplet • JWindow • Panel • Frame • Applet • Window Containers STEP 1 Containers are special components that may contain other components. Note: Containment is not the same as inheritance extension. A Frame may contain buttons, but buttons are not subclasses of Frame.

  14. Containers (Cont’d) • A Container is a class that extends from java.awt.Container • As it turns out, the class "Container" is itself a Component. • Containers can have: • Layouts set on them (discussed later) • Other components or containers added to them. Object Component Container

  15. Containers: An Example Let’s make a simple Frame. When working with GUIs, you often have to consult the API. Note the inheritance structure of your classes.

  16. Containers: An Example (Cont’d) • So far, we’ve used the API to learn how to make a Frame. • We found constructors for: • public Frame (); • public Frame (String strTitle); • Now, how can we set the size of the Frame? • We again return to the API.

  17. Containers: An Example (Cont’d) The class java.awt.Frame does not contain a method to set its size. But such a method was inherited from java.awt.Component:

  18. Containers: An Example (Cont’d) Likewise, there’s no method in java.awt.Frame to make the Frame visible. Instead, we find the method "show()" was inherited from java.awt.Window

  19. Hello GUI – The Program import java.awt.*; public class HelloGUI { public static void main (String[ ] arg) { System.out.println("About to make GUI"); Frame f = new Frame ("Hello GUIs"); f.setSize( 200, 200 ); f.show(); System.out.println("Finished making GUI"); } // main() } // class HelloGUI

  20. Hello GUI – The Program (Cont’d) Our program runs, and the frame never goes away. When we reach the end of main (as our print statement indicates) why doesn’t the program end?

  21. Hello GUI – The Program (Cont’d) import java.awt.*; public class HelloGUI { public static void main (String[ ] arg) { System.out.println ("About to make GUI"); Frame f = new Frame ("Hello GUIs"); f.setSize( 200, 200 ); f.show(); System.out.println ("Finished making GUI"); }// main }// class HelloGUI When the Java VM created our Frame, it entered into a kind of ‘infinite loop’, waiting for input and events. (This is common for all graphical toolkits.) while(true){ //get user input // handle event } Since we didn’t write any event handlers, not even the "window disposal" button will work.

  22. Hello GUI – The Program (Cont’d) Solution: To fix this problem, we’ll have to write some event handling code. But in order to write some event handling code, we have to create some components… So, for now, you’ll just have to use Ctrl-C to end the program. Once the basics of GUI construction are covered, we’ll return to this problem.

  23. 1. Inheritance -- our class extends a container 2. Composition -- our class holds a container GUI Design Idea We really have two choices when working with top-level containers: java.awt.Frame MyGUI MyGUI java.awt.Frame

  24. We save our single inheritance Check the API Will call constructor, so the show() method gets called GUI Design Idea: Example import java.awt.*; public class HelloComposition { Frame f; public HelloComposition() { f = new Frame("Composition Test"); f.setSize(200,200); f.setBackground(Color.red); f.show(); } public static void main(String[] args) { HelloComposition h = new HelloComposition(); } }

  25. GUI Design Idea: Example A few changes allows us to convert between the two solutions: import java.awt.*; public class HelloInheritance extends Frame { Frame f; public HelloInheritance(){ f = new Frame super("Composition Test"); f this.setSize(200,200); f this.setBackground (Color.red); f this.show(); } public static void main (String[] args) { HelloInheritance h = new HelloInheritance(); } } Note: Even the statement this. could be safely removed!

  26. Which Solution Works Better? Composition Inheritance • Saves the single inheritance • Use up our single inheritance • "Wasted inheritance" occurs where we subclass, but fail to override anything. • Useful when you want the "factory settings" for a GUI, with no changed behavior • Easier to change basic GUI behavior • Often requires more code, more references

  27. myFrame.setBackground(Color.red); An inherited method A class, also in the API Container Summary • Creating containers requires careful study of the API. Watch the inheritance structure of the classes. • A top-level container, like a Frame, requires event handlers (covered later). • There are many useful methods for customizing containers. Just look them up in the API documentation:

  28. Container Summary We may often use "composition" where: -- We don’t anticipate changing behaviors -- We need to save our single inheritance We may often use "inheritance" where: -- We need to change basic GUI behaviors

  29. Components STEP 2 • Most interactionsin a Java GUI are with Components. • Another generic term for Component in other GUIs • (e.g. X Windows) is "widget". • Different types of components for different types of • interaction (e.g. buttons, etc.) • User interactions with components create events (thus, allow event-driven programming) • As a rule, a Component cannot have other components inside: • Exceptions to rule:pop up menus may have menu items added to them. And Containers are themselves components due to inheritance.

  30. Component Examples Demo: HelloWidget

  31. Recall: A Container "is a" Component Component Examples (Cont’d) Component - generic widget that you can interact with Button - a widget that you can press Canvas - a widget that you can draw on Checkbox - a widget that is checked or not checked Choice - an option menu that drops down Container - a generic class that contains Components Panel - a Container to be used inside another container; used to split an existing window Label - a single line of read-only text List - a list of Strings Scrollbar - a horizontal or vertical scrollbar TextComponent TextArea - multi-line editable text TextField - single-line editable text

  32. Component Examples (Cont’d) • Canvas: • Typically a drawing surface on which shapes, graphs, pictures, etc can be drawn. • Utilize mouse events and mouse motion events to interact with the user to accomplish the drawing tasks. • TextField: • A one-line data entry area. • Theoretically infinite in length. • Can generate Key events to indicate that the user has typed a key. • More typically, it generates an Action event when the user finishes the data entry and hits Returnin the TextField.

  33. Component Examples (Cont’d) • Button: • Simply a clickable component. • Appears as a standard button on whatever graphical environment the user happens to be running at the time. • Generates an Action event when clicked. • Label: • A one-line field of text. • User cannot change this text directly; program changes text with setText( ) method. • Usually not used to capture events (but could). • Usually used as a one-way information source to provide a message to the user.

  34. Joining Components & Containers Containers have a method: public void add (Component c) that allows us to place items inside. Thus: Panel p = new Panel(); Button b1 = new Button ("Example 1"); Button b2 = new Button ("Example 2"); p.add (b1); p.add(b2); In this example, two buttons are added to the panel.

  35. An Example import java.awt.*; public class HelloComponent { Frame f; public HelloComponent(){ f = new Frame("Component Test"); f.setSize(200,200); f.setBackground(Color.red); Panel p = new Panel(); Button b = new Button("Hello Components"); p.add(b); f.add(p); f.show(); } public static void main (String[] args) { new HelloComponent(); } }

  36. Layout Managers STEP 3 We can now create Components and Containers. But how can they be organized? We might be tempted to call methods that set the x, y location of a component in a container. Consulting the API, we find some likely methods: public void setLocation(int x, int y); public void setSize(int width, int height);

  37. 75 pixels down Click 25 pixels over Layout Managers: Motivation • To arrange items, one could specify the location of a Component by specific x and y coordinates. The Component class contains the method setLocation(int width, int height): • Frame f = new Frame(); • f.setSize(500,500); • Button myButton = new Button ("Click"); • add(myButton); • myButton.setLocation(25, 75); What’s wrong with this approach??? NOTE:Origin 0,0 at top left! Note: Button’s x and y coordinate starts from top left

  38. Layout Managers: Motivation (Cont’d) • Problems with specifying (x, y) coordinates for Components: • This becomes tedious for even mildly complex GUIs. • Addition of more components requires recalculation of every component’s x, y coordinate. • If container resizes (e.g., user expands window), calculations have to be redone! • Solution: • Position components based on a percentage of available container size. Or create an algorithm to place components . . . • But Java already does this for you !!!

  39. Layout Managers: AWT-Based • Java provides several layout managers. • We will concentrate here on several of them: • BorderLayout • GridLayout • FlowLayout • BoxLayout • To tell a container which layout manager to use, invoke the method: • setLayout( ); • and specify a type of layout. • For example: • To specify a BorderLayout: • setLayout (new BorderLayout());

  40. Layout Managers: Two General Flavors • One can conceptually divide layout managers into two types: • Those that attach constraints to their components. • Those that do not. • What does this mean, "attach constraints“? If a manager attaches constraints to a component, then information about a component’s location (e.g., compass points) is stored with the object.

  41. Layout Managers: Constraints • BorderLayout specifies constraints corresponding to compass regions of a container: NORTH WEST EAST CENTER SOUTH

  42. Layout Managers: Constraints (Cont’d) • BorderLayout then appends constraint information on all components, e.g.: this.setLayout (new BorderLayout()); Button e = new Button ("East"); Button w = new Button ("West"); Button n = new Button ("North"); add(e, "East"); // deprecated add("West", w); // works; deprecated add(n, BorderLayout.NORTH); // preferred

  43. Layout Managers: Constraints (Cont’d)

  44. Layout Managers: Another Example import java.awt.*; public class Test extends Frame { public Test() { super ("BorderLayout Demo"); this.setSize(200,200); this.setLayout(new BorderLayout()); this.add (new Button ("North"), BorderLayout.NORTH); this.add (new Button ("South"), BorderLayout.SOUTH); this.add (new Button ("East"), BorderLayout.EAST); this.add (new Button ("West"), BorderLayout.WEST); this.add (new Button ("Center"), BorderLayout.CENTER); } public static void main (String[ ] args) { new Test().show(); } } // Test

  45. Layout Managers: Another Example (Cont’d) Program Output:

  46. BorderLayout NORTH WEST CENTER EAST SOUTH BorderLayout specifies the arrangement: • To add components to a BorderLayout, specify the position in which the component will reside. • Only one component (or container) can go in each of the five positions.

  47. BorderLayout: An Example • setLayout (new BorderLayout()); • add(new Label ("Hello!"), "North"); • Canvas myCanvas = new Canvas(); • // more about Canvas in a moment • add (myCanvas, "Center"); Hello! { a fresh canvas for drawing here}

  48. BorderLayout: Simple Example import java.awt.*; public class HelloLayout { public static void main(String[] args) { Frame f = new Frame(); f.setSize(400,400); BorderLayout bord = new BorderLayout(); f.setLayout(bord); Button b = new Button ("Hello"); f.add(b, BorderLayout.SOUTH); } } // HelloLayout Will this work? Let’s run it and find out...

  49. BorderLayout: Simple Example (Cont’d) import java.awt.*; public class HelloLayout { public static void main(String[] args) { Frame f = new Frame(); f.setSize(400,400); BorderLayoutbord = new BorderLayout(); f.setLayout(bord); Button b = new Button ("Hello"); f.add(b, BorderLayout.SOUTH); f.show(); } } // HelloLayout Ahh.. We forgot to set our Frame visible. Now it works. Welcome to the exciting world of GUI debugging.

  50. Layout Managers: No Constraints • The second type of LayoutManager does not specify constraints for the objects it holds. • Examples: • GridLayout() • FlowLayout() • Without constraints, you cannot accurately predict layout behavior across platforms.

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