GWT training session 2

GWT Training – Session II

Client-Side Implementation

Snehal Masne
www.TechProceed.com

Contents
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The User Interface
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Static widgets
Form widgets
Complex widgets
Panels

This are slides are based from the book “Google Web Toolkit Applications” by Ryan Desbury, 2008, Pearson Education

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The User Interface
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GWT contains classes for building dynamic
re-usable components (called widgets) based
upon web browser's user interface features
The user interface framework is similar to
Java AWT/Swing
For the purpose of this tutorial, we divide the
different types of widgets into four categories
– Static widgets, form widgets, complex
widgets and panels
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The User Interface Groups

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Static Widgets
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They do not have any internal state or
change dynamically on their own
Can be part of a dynamic user interface in
which the user interface code can change
their properties and location at runtime, but
not as a result of user actions
Includes
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Label
HTML
Image
Hyperlink
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The Entry-Point Class
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Before we start building our user interface, we need to understand the EntryPoint Class
Think of this class as the main class of your application with the java main()
method that the JVM invokes first
The Entry-Point class contains onModuleLoad() method which is the method that
the GWT compiler calls first
The class implements com.google.gwt.core.client.EntryPoint interface
For the GWTTraining project, GWTTraining.java is the Entry-Point class (which
is defined in the application's GWT configuration file)‫‏‬

import com.google.gwt.core.client.EntryPoint
public class GWTTraining implements EntryPoint {
public void onModuleLoad() {
//your initial code goes here
}
}
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Label
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A widget that contains arbitrary text, not interpreted as HTML. This widget uses a <div> element,
causing it to be displayed with block layout
Open the GWTTraining project in Eclipse
Create a new Entry Point class called GWTTrainingWidget under File > New. We would use this entry
class for our widgets tutorial.
In the GWTTraining.gwt.xml configuration file, delete the entry-point definition for
my.utm.kase.gettraining.client.GWTTraining. We only want to display the GWTTrainingWidgets entrypoint when we run the applicaiton.
Also edit the GWTTraining.html and delete the contents of the <body> tag so that we start from an
empty page.
Add the following import statements
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;
Add the following code in the onModuleLoad() method
Label label = new Label("Welcome to CASE, UTM");
RootPanel.get().add(label);
The code creates a new label widget and adds it to the root panel
A‫‏‬simple‫‏‬text‫“‏‬Welcome‫‏‬to‫‏‬CASE,‫‏‬UTM”‫‏‬is‫‏‬displayed‫‏‬when‫‏‬you‫‏‬run‫‏‬the‫‏‬application.

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Label – Embellishing with CSS
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A great feature of GWT is letting you to achieve great presentations using CSS
GWT widgets have default CSS names that let you set their style
The label widget CSS is .gwt-Label { }
Add the following to the /war/GWTTraining.css to change the appearance of the
label widget:
.gwt-Label{
background-color:silver;
color:green;
text-align-center;
border-style:groove;
border-width:thick;
border-color:navy;
}

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If you use the default GWT CSS names for the widgets, all widgets of the same
class are affected.
To demonstrate this, let's create another label widget by adding the following
code in the GWTTrainingWidgets.java file:
Label label2 = new Label("Where Advanced Learning Begins");
RootPanel.get().add(label2);
label2 also has the same appearance as the first label because it also inherits from .gwtLabel CSS name.

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
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We can apply a different style for a particular label instead of the general class definition
To demonstrate that add the following custom CSS definition in GWTTraining.css
.label2 {
background-color:orange;
border-style:ridge;
border-width:thick;
border-color:navy;
}
Add the following code to set the style to label2 (before adding it to the root panel:
label2.setStylePrimaryName("label2");
When you refresh the browser you will see that label2 now has its own customized style.
Styling with CSS is the same for all the other widgets in GWT. The default style names of
the widgets can be found in the GWT API Java documentation.

Info: CSS is a very powerful language that gives the web great look and feel. Because it is separated from the content (usually
HTML), customizing the pages becomes very flexible. For further reading you may want to check: The Ultimate CSS
reference

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Customizing programatically
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Some properties of the Label (and other
widgets as well) can be customized
programatically

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HTML Widget
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Used for rendering HTML
Add the following codes to GWTTrainingWidgets.java
RootPanel.get().add(new HTML("<hr/>"));
//add a horizontal line break
RootPanel.get().add(new HTML("<b>CASE in bold</>")); //add bold text
RootPanel.get().add(new HTML("<a href='http://www.case.utm.my'>Find
more about CASE</a>"));
//add a horizontal line break
Add import statement for com.google.gwt.user.client.ui.HTML
Refresh the browser to view the changes
The HTML widget can be customized using CSS just like the Label widget. The default CSS
name is .gwt-HTML

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The Image Widget
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Accepts a URL pointing to an image file and renders it
Create images folder: /war/gwttraining/images.
Add case_logo.jpg to the folder which is provided in the training resources CD
Add the following code:
String url = GWT.getModuleBaseURL() + "images/case_logo.jpg";
Image image = new Image(url);
RootPanel.get().add(image);

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CSS default style name is .gwt-Image

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The Image Widget
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Add the following code to display image from an external server:
RootPanel.get().add(new
Image("http://www.case.utm.my/v2/images/intro_pic/case_intro_pic_1%20copy.g
if"));
The following output should be displayed when the browser is refreshed

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The Form Widgets
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Widgets typically used with HTML forms
Unlike traditional HTML forms, data is submitted to the server asynchrnously
without refreshing the page
GET form widgets can be used in ways similar to desktop applications and not
necessarily inside a HTML form
The widgets include:
 Button, CheckBox, RadioButton, ListBox, TextBox
 PasswordTextBox, TextArea, FileUpload, Hiddein
 ToggleButton, PushButton, SuggestBox and RichTextArea

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The Button Widget
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Wraps‫‏‬the‫‏‬HTML‫‏‬form‫‏‬input‫‏‬with‫‏‬the‫‏‬type‫‏‬button‫<(‏‬input‫‏‬type=”button”>)‫‏‬
Can be used to invoke any action in the application
To see the Button widget in action add the following code:
Button alertButton = new Button("Alert"); //create the button
alertButton.addClickHandler( new ClickHandler() { //handle event
@Override
public void onClick(ClickEvent event) {
//handle button event here
Window.alert("Alert button clicked!");
}
});
//add alertButton to root widget
//add a horizontal line
RootPanel.get().add(alertButton);
//add button to root panel
Just like other GWT widgets, the Button widget events are handled using the Observer pattern
The observer (Event handler) observes the state of the subject (the user interface, e.g Button).
When‫‏‬the‫‏‬subject’s‫‏‬state‫‏‬changes,‫‏‬the‫‏‬observer‫‏‬is‫‏‬notified.
The default CSS name is .gwt-Button

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ToggleButton and PushButton
Widget
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Both similar to Button widget
When ToggleButton is clicked it remains in a 'pressed state' until clicked again
A PushButton supports customization of its look based on its state
//toggle and push buttons
ToggleButton toggleButton = new ToggleButton("Toggle me");
PushButton pushButton = new PushButton("I'm a push button");
pushButton.setSize("150", "40");
RootPanel.get().add(toggleButton);
RootPanel.get().add(pushButton);



You‫‏‬can‫‏‬set‫‏‬some‫‏‬widget‫‏‬properties‫“‏‬programmatically”‫‏‬without‫‏‬using‫‏‬CSS‫‏‬
definition just as is done above in setting the size of the PushButton. However
using CSS is the most recommended because it separates the presentation from
the Java code which improves flexibility and maintainability.

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Button Widgets with Images
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You may create buttons (Button, ToggleButton or PushButton) with images instead of
text captions
ToggleButton can be created with two images so that they can be represented in
pressed and released states.
ToggleButton imgToggleButton = new ToggleButton(
new Image(GWT.getModuleBaseURL() + "images/h_toggle.jpg"),
new Image(GWT.getModuleBaseURL() + "images/v_toggle.jpg")‫‏‬
);
imgToggleButton.setSize("60", "60");
//add a horizontal line
RootPanel.get().add(imgToggleButton);
//add imgToggleButton to
//root panel
Copy the h_toggle.jpg and v_toggle.jpg to /war/gwttraining/images

Released State

Pressed State
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Styling Button States with Css
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You can use CSS to generate different styles for ToggleButton and PushButton
based on their states
The default names for the states are shown in table below:

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Checkbox Widget
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Wraps‫‏‬HTML’s‫‏‬check‫‏‬box‫‏‬input‫‏‬tag‫<(‏‬input‫‏‬type=”button”>)‫‏‬
Has two states - Checked/Unchecked
You can programmatically set the state with the setChecked method by passing true for
checked or false for unchecked
Supports focus behavior and click events
Default CSS name is .gwt-Checkbox

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Checkbox Widget - Code
Sample
//checkbox widget
final CheckBox checkBox = new CheckBox("Do u love GWT?");
checkBox.addClickHandler( new ClickHandler() {
@Override
//handle event
if( checkBox.getValue() ) {
Window.lert("Yeah, welcome to the world of GWT");
}
else {
Window.alert("Sorry, u are missing a lot. U gotta think again");
}
}
});
RootPanel.get().add(checkBox);

//add a horizontal break line

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RadioButton Widget
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Usually belongs to a group of other
RadioButtons so that only one selection can
be made

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RadioButton Widget – Sample
Code
//radio button widget
final RadioButton redButton = new RadioButton("color", "red");
final RadioButton orangeButton = new RadioButton("color", "orange");
final RadioButton greenButton = new RadioButton("color", "green");
final Label label3 = new Label("");
label3.setSize("25", "25");
label3.setStylePrimaryName("label3");
ClickHandler radioButtonsHandler = new ClickHandler() {
@Override
if( event.getSource() == redButton ) {
label3.setStylePrimaryName("red");
}
else if( event.getSource() == orangeButton ) {
label3.setStylePrimaryName("orange");
}
else {
label3.setStylePrimaryName("green");
}
}
};
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RadioButton Widget – Sample
Code (cont'd)‫‏‬
redButton.addClickHandler(radioButtonsHandler);
orangeButton.addClickHandler(radioButtonsHandler);
greenButton.addClickHandler(radioButtonsHandler);
RootPanel.get().add(new HTML("<hr/>")); //add a horizontal break line
//add to root panel
RootPanel.get().add(label3);
RootPanel.get().add(redButton);
RootPanel.get().add(orangeButton);
RootPanel.get().add(greenButton);
CSS Stlye
.label3 {
border-style:groove;
width: 25px;
height: 25px;
}
.red {
background-color:red;
}
.orange {
background-color:orange;
}
.green {
background-color:green;
}
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ListBox Widget
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A group of options in a form of list in which
only one option can be selected
Two forms:



Normal list
Drop down list

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ListBox Widget – Sample Code
final ListBox colorList = new ListBox();
colorList.addItem("Red");
colorList.addItem("Orange");
colorList.addItem("Green");
colorList.addChangeHandler( new ChangeHandler() {
@Override
public void onChange(ChangeEvent event) {
if( colorList.getSelectedIndex() == 0 ) {
label3.setStylePrimaryName("red");
redButton.setValue(true);
}
else if( colorList.getSelectedIndex() == 1 ) {
label3.setStylePrimaryName("orange");
orangeButton.setValue(true);
}
else {
label3.setStylePrimaryName("green");
greenButton.setValue(true);
}
}
});

RootPanel.get().add(new HTML("<hr/>")); //add a horizontal break line
RootPanel.get().add(colorList);
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ListBox Sample Code – cont'd
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The previous code displays the drop down
format of the ListBox
Use the following code to change to the
normal format:
//change the list box format
colorList.setVisibleItemCount(3);

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SuggestBox Widget
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A text box with drop-down suggestions based
on the word that you type
Usually used when the list of items are too
much to be displayed at a time
E.g. Google Suggest
Uses SuggestOracle instance to plug in
dynamic results from datasource on the
server
MultiWordSuggestOracle can be used if the
suggest list is generated at the client side
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SuggestBox – Sample Code
//SuggestBox
String suggestString = "The Faculty of Computer Science and Information "
+ "Systems, UTM provides specialist teaching and conducts research "
+ "in fundamental and applied computer science, software "
+ "engineering, artificial intelligence and cognitive science. "
+ "We are proud to deliver outstanding undergraduate and "
+ "postgraduate education that offers varied and exciting "
+ "career opportunities around the world.";
String words[] = suggestString.split(" ");
MultiWordSuggestOracle suggestOracle = new MultiWordSuggestOracle();
suggestOracle.addAll(Arrays.asList(words));
SuggestBox suggestBox = new SuggestBox(suggestOracle);
RootPanel.get().add(suggestBox);


CSS Styles
.gwt-SuggestBox {}
.gwt-SuggestBoxPopup { border: 2px solid #C3D9FF; background-color:#E8EEF7; }
.gwt-SuggestBoxPopup .item { }
.gwt-SuggestBoxPopup .item-selected { background-color:#C3D9FF;}
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TextBox Widget
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Encapsulates‫‏‬HTML’s‫‏‬input‫‏‬tag‫‏‬with‫‏‬type‫‏‬input‫<(‏‬input‫‏‬type=”input”>)

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Typically used for capturing small text input from user
//TextBox widget
final TextBox emailBox = new TextBox();
emailBox.setText("<Enter your email>");
emailBox.setStylePrimaryName("emailBox-blank");
//add focus gain handler
emailBox.addFocusHandler( new FocusHandler() {
@Override
public void onFocus(FocusEvent event) {
String emailText = emailBox.getText();
if( emailText.equals("<Enter your email>")) {
emailBox.setText("");
}
emailBox.removeStyleName("emailBox-blank");
}
});
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TextBox Widget – cont'd
//add focus lost handler
emailBox.addFocusListener(new FocusListenerAdapter() {
public void onLostFocus(Widget sender) {
String emailText = emailBox.getText();
if( emailText.equals("")) {
emailBox.setStylePrimaryName("emailBox-blank");
emailBox.setText("<Enter your email>");
}
}
});
RootPanel.get().add(emailBox);


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PasswordTextBox Widget
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Similar to TextBox but its contents are hidden
to protect sensitive data
//PasswordTextBox widget
PasswordTextBox passwordBox = new PasswordTextBox();
RootPanel.get().add(passwordBox);

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TextArea Widget
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Similar to TextBox but contents can span
multiple pages
//TextArea widget
TextArea textArea = new TextArea();
textArea.setCharacterWidth(80);
textArea.setVisibleLines(10);
RootPanel.get().add( textArea );

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FileUpload Widget
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Encapsulates‫‏‬HTML’s‫‏‬input‫‏‬tag‫‏‬with‫‏‬its‫‏‬type‫‏‬
attribute set to file (<input type='file'>)‫‏‬
Allows users to select a file from their local
file system, usually to be uploaded to the
server
//FileUpload widget
FileUpload fileUpload = new FileUpload();
RootPanel.get().add( fileUpload );

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Hidden Widget
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Encapsulates‫‏‬HTML’s‫‏‬input‫‏‬tag‫‏‬of‫‏‬type‫‏‬
hidden (<input type='hidden'>)‫‏‬
It is used with the FormPanel to submit a
form asynchronously to the server.

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Complex Widgets
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User interface widgets in web pages that do
not have HTML tag equivalents.
They are created by compositing HTML tags
together and handling user events through
JavaScript to emulate more
sophisticated widgets.
GWT has some complex widgets in its library
Advanced custom widgets can also be built
with GWT
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Tree Widget
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Displays a hierarchical view of data that can
be expanded and collapsed similar to tree
widgets in desktop applications typically
You can add simple text or widgets as
children of the tree
The TreeItem widget can be used to achieve
several levels of hierarchy

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TreeWidget – Sample Code
//Tree Widget
Tree rootTree = new Tree();
TreeItem treeItem1 = new TreeItem("Contact 1");
treeItem1.addItem(new Image(GWT.getModuleBaseURL() + "images/contact.jpg"));
treeItem1.addItem(new Image(GWT.getModuleBaseURL() +
"images/mail.jpeg"));
TreeItem treeItem2 = new TreeItem("Contact 2");
treeItem2.addItem(new Image("images/contact.jpg"));
treeItem2.addItem(new Image("images/mail.jpeg"));
rootTree.addItem(treeItem1);
rootTree.addItem(treeItem2);
RootPanel.get().add( rootTree );
CSS Style Rules
.gwt-Tree {}
.gwt-Tree .gwt-TreeItem {}
.gwt-Tree .gwt-TreeItem-selected {}
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MenuBar Widget
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Similar to menu bars on desktop applications
Displays list of menus to be selected
//MenuBar widget
MenuBar lecturerMenu = new MenuBar(true); //orient vertically
lecturerMenu.addItem("Save Records" , new Command() {
public void execute() {
Window.alert("Saved");
}
});
MenuBar studentMenu = new MenuBar(true); //orient vertically
studentMenu.addItem("Register" , new Command() {
//add register event
}
});

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MenuBar Widget – cont'd
studentMenu.addItem("View Records" , new Command() {
//view records event
}
});
MenuBar menu = new MenuBar();
menu.addItem("Lecturer", lecturerMenu);
menu.addItem("Student", studentMenu);
RootPanel.get().add(menu, 0, 0);

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MenuBar Widget – CSS Styles
.gwt-MenuBar {
background-color:#F3F5F6;
border: 1px;
}
.gwt-MenuBar .gwt-MenuItem {
font-size: 9pt;
cursor:hand;
cursor:pointer;
padding:2px 5px 2px 5px;
margin:0px;
}
.gwt-MenuBar .gwt-MenuItem-selected {
background-color:#316AC5;
color:white;
}

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Simple Layout Panels
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Panels are used to organize the layout of the
various widgets we have covered so far.
GWT has several layout widgets that provide
this functionality
The simple Layout Panels include:

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FlowPanel
VerticalPanel
HorizontalPanel

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FlowPanel
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

It functions like the HTML layout
Child widgets of the FlowPanel are displayed
horizontally and then wrapped to the next row
down when there is not enough horizontal room
left
//FlowPanel
FlowPanel flowPanel = new FlowPanel();
for( int i = 1; i <= 20; i++ ) {
flowPanel.add(new Button("Button " + String.valueOf(i)));
}
RootPanel.get().add(flowPanel);

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FlowPanel – cont'd
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If you run the code and resize the browser window
smaller, you will see that the child widgets (buttons)
are displaced to the next row when the space
becomes insufficient to display in one row
The result is opposite if you resize the window
bigger

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HorizontalPanel and
VerticalPanel
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

HorizontalPanel is similar to FlowPanel but
uses scrollbar to display its widgets if there is
no enough room instead of displacing to the
next row
VerticalPanel organizes its child widgets in a
vertical orientation

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HorizontalSplitPanel and
VerticalSplitPanel


They are divided into two panels that be
resized

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FlexTable and Grid Widgets
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Encapsulates HTML's table tag (<table />)‫‏‬
They display child widgets in a grid spanning
vertically and horizontally.
The Grid widget enforces an explicitly set
number of rows and cells for each row.
The FlexTable is more flexible, allowing cells
to be added as needed, rows to have a
variable number of cells, and cells to span
multiple rows or columns
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FlexTable and Grid Widgets –
cont'd
//Grid
Grid grid = new Grid(3,3);
for( int i = 0; i < 3; i++) {
for( int j = 0; j < 3; j++ ) {
grid.setWidget(i,j,new Image(GWT.getModuleBaseURL() +
"images/tree2.jpg"));
}
}
//FlexTable
FlexTable flexTable = new FlexTable();
flexTable.setWidget(0,0, new HTML("Flex Table Widget"));
flexTable.getFlexCellFormatter().setColSpan(0, 0, 4);
for( int i = 0; i < 4; i++ ) {
flexTable.setWidget(1, i, new Image(GWT.getModuleBaseURL() +
"images/tree.jpeg"));
}

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FlexTable and Grid Widgets –
cont'd
flexTable.setWidget(2,0, new Image(GWT.getModuleBaseURL() + "images/tree2.jpg"));
flexTable.setWidget(2,1, new Image(GWT.getModuleBaseURL() + "images/tree2.jpg"));
flexTable.setWidget(3, 0, new Image(GWT.getModuleBaseURL() +
"images/tree_big.png"));
HorizontalSplitPanel hSplitPanel = new HorizontalSplitPanel();
hSplitPanel.setLeftWidget(flexTable);
hSplitPanel.setRightWidget(grid);
RootPanel.get().add(hSplitPanel);

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Customizing the Widgets
HorizontalSplitPanel hSplitPanel = new HorizontalSplitPanel();
hSplitPanel.setLeftWidget(flexTable);
hSplitPanel.setRightWidget(grid);
RootPanel.get().add(hSplitPanel);
//vertical panel 2
VerticalPanel vPanel2 = new VerticalPanel();
vPanel2.add(rootTree);
vPanel2.add(flowPanel);
RootPanel.get().add(vPanel2);

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Customizing the Widgets –
cont'd
//vertical panel 3
HorizontalPanel hPanel2 = new HorizontalPanel();
hPanel2.add(checkBox);
hPanel2.add(label3);
hPanel2.add(redButton);
hPanel2.add(orangeButton);
hPanel2.add(greenButton);
hPanel2.add(colorList);
VerticalPanel vPanel4 = new VerticalPanel();
vPanel4.add(textArea);
vPanel4.add(fileUpload);
RootPanel.get().add(vPanel4);

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TabPanel


Displays just one of its child widgets at a time and provides controls to select the
child to display
//TabPanel
TabPanel tabPanel = new TabPanel();
tabPanel.add(vPanel2, "Buttons");
tabPanel.add(hPanel2, "Options");
tabPanel.add(vPanel4, "Text");
tabPanel.setSize("100%", "100%");
RootPanel.get().add(tabPanel);

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Other Widgets
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


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

DeckPanel
DockPanel
StackPanel
HTMLPanel
LazyPanel
Composite
SimplePanel
ScrollPanel
FocusPanel
FormPanel
DisclosurePanel
PopupPanel
DialogBox

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This brings us to the end of the 2nd session of
the GWT Training. In the next session we
would learn how to establish communication
between the client and server.

Thank you

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GWT training session 2

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