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GWT - Button Widget
Introduction
The Button widget represents a standard push button.
Class Declaration
Following is the declaration for com.google.gwt.user.client.ui.Button class −
public class Button extends ButtonBase
CSS Style Rules
Following default CSS Style rule will be applied to all the Button widget. You can override it as per your requirements.
.gwt-Button { }
Class Constructors
Sr.No. | Constructor & Description |
---|---|
1 |
Button() Creates a button with no caption. |
2 |
protected Button(Element element) This constructor may be used by subclasses to explicitly use an existing element. |
3 |
Button(java.lang.String html) Creates a button with the given HTML caption. |
4 |
Button(java.lang.String html, ClickListener listener) Creates a button with the given HTML caption and click listener. |
Class Methods
Sr.No. | Function name & Description |
---|---|
1 |
click() Programmatic equivalent of the user clicking the button. |
2 |
static Button wrap(Element element) Creates a Button widget that wraps an existing <a> element. |
Methods Inherited
This class inherits methods from the following classes −
com.google.gwt.user.client.ui.UIObject
com.google.gwt.user.client.ui.Widget
com.google.gwt.user.client.ui.FocusWidget
com.google.gwt.user.client.ui.ButtonBase
java.lang.Object
Button Widget Example
This example will take you through simple steps to show usage of a Button Widget in GWT. Follow the following steps to update the GWT application we created in GWT - Create Application chapter −
Step | Description |
---|---|
1 | Create a project with a name HelloWorld under a package com.tutorialspoint as explained in the GWT - Create Application chapter. |
2 | Modify HelloWorld.gwt.xml, HelloWorld.css, HelloWorld.html and HelloWorld.java as explained below. Keep rest of the files unchanged. |
3 | Compile and run the application to verify the result of the implemented logic. |
Following is the content of the modified module descriptor src/com.tutorialspoint/HelloWorld.gwt.xml.
<?xml version = "1.0" encoding = "UTF-8"?> <module rename-to = 'helloworld'> <!-- Inherit the core Web Toolkit stuff. --> <inherits name = 'com.google.gwt.user.User'/> <!-- Inherit the default GWT style sheet. --> <inherits name = 'com.google.gwt.user.theme.clean.Clean'/> <!-- Specify the app entry point class. --> <entry-point class = 'com.tutorialspoint.client.HelloWorld'/> <!-- Specify the paths for translatable code --> <source path = 'client'/> <source path = 'shared'/> </module>
Following is the content of the modified Style Sheet file war/HelloWorld.css.
body { text-align: center; font-family: verdana, sans-serif; } h1 { font-size: 2em; font-weight: bold; color: #777777; margin: 40px 0px 70px; text-align: center; } .gwt-Button { color:red; } .gwt-Green-Button { color:green; } .gwt-Blue-Button { color:blue; }
Following is the content of the modified HTML host file war/HelloWorld.html.
<html> <head> <title>Hello World</title> <link rel = "stylesheet" href = "HelloWorld.css"/> <script language = "javascript" src = "helloworld/helloworld.nocache.js"> </script> </head> <body> <h1>Button Widget Demonstration</h1> <div id = "gwtContainer"></div> </body> </html>
Let us have following content of Java file src/com.tutorialspoint/HelloWorld.java which will demonstrate use of Button widget.
package com.tutorialspoint.client; import com.google.gwt.core.client.EntryPoint; import com.google.gwt.event.dom.client.ClickEvent; import com.google.gwt.event.dom.client.ClickHandler; import com.google.gwt.user.client.Window; import com.google.gwt.user.client.ui.Button; import com.google.gwt.user.client.ui.RootPanel; import com.google.gwt.user.client.ui.VerticalPanel; public class HelloWorld implements EntryPoint { public void onModuleLoad() { //create buttons Button redButton = new Button("Red"); Button greenButton = new Button("Green"); Button blueButton = new Button("Blue"); // use UIObject methods to set button properties. redButton.setWidth("100px"); greenButton.setWidth("100px"); blueButton.setWidth("100px"); greenButton.addStyleName("gwt-Green-Button"); blueButton.addStyleName("gwt-Blue-Button"); //add a clickListener to the button redButton.addClickHandler(new ClickHandler() { @Override public void onClick(ClickEvent event) { Window.alert("Red Button clicked!"); } }); //add a clickListener to the button greenButton.addClickHandler(new ClickHandler() { @Override public void onClick(ClickEvent event) { Window.alert("Green Button clicked!"); } }); //add a clickListener to the button blueButton.addClickHandler(new ClickHandler() { @Override public void onClick(ClickEvent event) { Window.alert("Blue Button clicked!"); } }); // Add button to the root panel. VerticalPanel panel = new VerticalPanel(); panel.setSpacing(10); panel.add(redButton); panel.add(greenButton); panel.add(blueButton); RootPanel.get("gwtContainer").add(panel); } }
Once you are ready with all the changes done, let us compile and run the application in development mode as we did in GWT - Create Application chapter. If everything is fine with your application, this will produce following result −
When you click Click Me button, it will show an alert message Hello World!