[[using-uri-fragments]]
Using URI fragments
-------------------

[[reading-fragment-when-initializing-ui]]
Reading Fragment when Initializing UI
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

URI fragments can either be used for initializing the UI and/or read or
modified in any listener. In the UI.init method you get a "VaadinRequest
request" parameter. The UI's Page contains a information about the HTTP
request used to initialize the application and you can get the URI
fragment using

....
getPage().geUriFragment()
....

A simple init that depends on the URI fragment is thus:

[source,java]
....
public class MyUI extends UI {
  @Override
  protected void init(VaadinRequest request) {
    layout = new VerticalLayout();
    layout.setMargin(true);
    setContent(layout);

    Label label = new Label("Hello, your fragment is "
            + getPage().getUriFragment());
    layout.addComponent(label);
  }
}
....

[[reading-fragment-changes]]
Reading Fragment Changes
~~~~~~~~~~~~~~~~~~~~~~~~

The URI fragment can be changed also when the application is running,
either manually in the location bar in browser or from user code. These
changes can be caught with a **FragmentChangedListener**. Notice,
however, that there is no event fired for the initial URL fragment. The
easiest way to handle both cases in the same way is to call the same
method from the FragmentChangedListener and the init method:

[source,java]
....
public class MyUI extends UI {
  // ...

  // React to fragment changes
  getPage().addUriFragmentChangedListener(new UriFragmentChangedListener() {
    @Override
    public void uriFragmentChanged(UriFragmentChangedEvent source) {
      handleFragment(source.getUriFragment());
    }
  });

  // Handle the fragment received in the initial request
  handleFragment(getPage().getUriFragment());

  addComponent(new Button("Show and set fragment", new Button.ClickListener() {
    @Override
      public void buttonClick(ClickEvent event) {
        handleFragment(getPage().getUriFragment());
        getPage().setUriFragment("customFragment");
      }
  }));
....

[[reading-and-writing-the-fragment]]
Reading and Writing the Fragment
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To later on read the fragment you can use

....
Page.getCurrent().getUriFragment();
....

and to set the fragment

....
Page.getCurrent().setUriFragment(String fragment);
....
