Hi Guys,
I have just implemented a multipage(basically multi url) website using
History. It works great using history token. But i need something else
from GWT which i am not able to solve.
Now when user clicks on something(link/button etc) i add the token to
History and my history callbacks get called.
Now in history value change handler i do something like this
1) FInd out what page need to be dispalyed(basically identify the
panels etc).
2) now each of my panel which can have history implementing
hasHistory(my own) interface, which has function
recoverPanelFromHistory.
3) In this function, i check if i have client side data cahced for
this panel, if yes then load it into panel and display it(basically
add to main panel widget tree).
4) But if no cache data found then go to server and get data.
one such implementation
@Override
public boolean recoverPanelFromHistory(Map<String, String>
historyTokens) {
String page = historyTokens.get(PAGE_PARAM);
boolean returnValue = false;
if("home".equalsIgnoreCase(page))
{
returnValue =
userHomePanel.recoverPanelFromHistory(historyTokens); //and this
function will calls its child panels if they support history
if(returnValue )
{
mainContentPanel.clear(); //clearing the
mainPanel view of client
mainContentPanel.add(userHomePanel); //and
adding the view
according to history token value
}
else
{
//dont change the browser view and stay at
current panel/view/page. This also means child panel can not be
recovered and there must be some problem with history tokens provided.
}
}
if("profile".equalsIgnoreCase(page))
{
returnValue =
prodilePanel.recoverPanelFromHistory(historyTokens); //and this
function will calls its child panels if they support history
if(returnValue )
{
mainContentPanel.clear(); //clearing the
mainPanel view of client
mainContentPanel.add(profilePanel); //and
adding the view
according to history token value
}
else
{
//dont change the browser view and stay at
current panel/view/page. This also means child panel can not be
recovered and there must be some problem with history tokens provided.
}
}
return returnValue;
}
So till now theoretically it sounds good and works good.
Problem starts when lets say user lost his Internet connection or call
fail at server because of any system level error..
userHomePanel.recoverPanelFromHistory(historyTokens);
This function does following things.
1) get the data from cache for this panel
2) if found call loadDataIntoPanel(data) function and load it into
panel and return true.
3) else call the server to get data.
Now server call is async and I need to return some value from
userHomePanel.recoverPanelFromHistory(historyTokens);, so if i return
true and call fails at server because of some network problem then
ideally i dont want to switch to new view as per this history action
but my function has already returned true and mainPanle has already
changed the view to new panel.
Now i dont want child panels to call parentPanel's method to tell them
later that server call was success or failure so that main parent
panel can decide whethere i should switch panels/view or not. If child
need to know parent then my all panels will be too much dependent on
each other and they will be too much crossed chain to each other.
If you see gmail it uses such features. If you have loaded ur inbox
and then you lost ur internet connection and then u click on any
email. Then gmail doesnt take you to single mail viewer page and then
tell "oh u lost ur connection" but it just keep you on inbox view and
keep trying and after some time stop trying.
How can i achieve such functionality.?
Are there any existing libraries to do that or any particular design
pattern is there?
Thanks, in advance
Ravi.
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