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Changing a textview text dynamically when it is displayed in a tabhost

Firstly, Im new to android but have years of various other programming experience on unix, windows,but not with Java or android.
Im wanting to display a tab with 3 tabs, each having a different layout file (which works).
Im working on displaying a "blank" template and then the data is retrieved from an XML file once the user points a setting to one (i.e. via shared preferences).
My problem is that the function populateXMLCharacter is never called (using breakpoints). The tab activity always displays "", which is a strig the string.xml.
Actually putting a breakpoint in the oncreate function never gets called either. Ive tried using a call to populateXMLCharacter in onResume, but it too never gets called.
Im thinking its because of the call to the tab:
Resources res = getResources(); // Resource object to get Drawables
TabHost tabHost = getTabHost(); // The activity TabHost
TabHost.TabSpec spec; // Resusable TabSpec for each tab
// Do this and the same for all tabs
spec = tabHost.newTabSpec("Description").setIndicator("Description",
res.getDrawable(R.drawable.android)).setContent(R.layout.tab_harp_description);
tabHost.addTab(spec);
Should I be using an intent? I thought the layout was created in a seperate function (in this case harpCSDescription.java and then this allows that activity to be inserted into the tabhost?
other functions:
public class harpcsDescription extends Activity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView (R.layout.tab_harp_description);
}
//#Override
protected void onResume()
{
// NOW WE ADD DATA TO THE TEMPLATE
populateXMLCharacter();
}
public void populateXMLCharacter()
{
Ive tried using intents in the following manner but it simply crashes before any breakpoints are reached.
http://developer.android.com/resources/tutorials/views/hello-tabwidget.html
Can some one please guide me to what I should be doing to create an activity with data that is retrieved AFTER the tab is created?

I think you need an intent. To attach an activity to a tab, write the following in the tab host:
Intent intent = new Intent(this, MyActivity.class);
and then in the tab spec write:
tabSpec = tabHost.newTabSpec("name").setIndicator(this.getString(R.string.name)).setContent(intent)
Then in the MyActivity class, you can specify the layout and load the XML data to populate the tab in the onCreate() method. You can use a different activity for each tab.

Removing a tab and the activity (intent) inside of it from a TabHost

I have an app that can create tabs dynamically. And when I create a tab I initiate an activity as an intent. Like so:
private void addTab(Context packageContext, Class<?> newClass, TabHost mTabHost, String tabId, String tabLabel){
// newClass is my Activity class that I want to start in the tab
Intent intent = new Intent().setClass(packageContext, newClass);
TabHost.TabSpec spec;
spec = mTabHost.newTabSpec(tabId).setIndicator(tabLabel)
.setContent(intent);
mTabHost.addTab(spec);
mTabHost.setCurrentTabByTag(tabId);
}
Pretty standard. And it works great. Now, suppose that I have a button (or menuitem, whatever) in the activity that I instantiated inside of my tab. When the user presses this button, I want the activity, and the tab it is inside of, to be removed and destroyed.
I can't seem to find a simple way to do this. I have found the TabHost.clearAllTabs() function, but this destroys all tabs and activities, I just want to remove one.
Someone suggested I save a list of all Tabs that I have opened, and then call clearAllTabs(), after which I recreate all of my other tabs except for the one I don't want.
Something like this:
public static ArrayList<TabHost.TabSpec> list = new ArrayList<TabHost.TabSpec>();
I add this line to my addTab() function so that every tab I create is remember in my ArrayList:
list.add(spec);
And then when I want to remove my tab I run this function:
public static void removeTab(){
list.remove(list.size()-1); // remove it from memory
mTabHost.clearAllTabs(); // clear all tabs from the tabhost
for(TabHost.TabSpec spec : list) // add all that you remember back
mTabHost.addTab(spec);
}
This removes my tab from my ArrayList, removes all tabs, then recreates all the tabs remaining using my ArrayList. In theory it should work, but I get the following error when I try call this function:
FATAL EXCEPTION: main
java.lang.NullPointerException
at android.widget.TabWidget.setCurrentTab(TabWidget.java:342)
at android.widget.TabWidget.focusCurrentTab(TabWidget.java:366)
at android.widget.TabHost.setCurrentTab(TabHost.java:323)
at android.widget.TabHost.addTab(TabHost.java:216)
at com.example.myapp.TabManager.removeTab(QuikBrowser.java:86)
at com.example.myapp.TabManager.TabWindow.onOptionsItemSelected(TabWindow.java:91)
at android.app.Activity.onMenuItemSelected(Activity.java:2205)
For some reason, when adding a tab, it attempts to set the current tab, and it hits a null pointer exception.
If you guys could suggest another way of achieving what I want to do, or a way to fix my current method, I would appreciate it.

Try changing current tab to 0.
Something like:
getTabHost().setCurrentTab(0);
getTabHost().clearAllTabs();
I was reading that calling clearAllTabs(); will throw a nullpointerexception if you don't set the tabhost to the first tab (.setCurrentTab(0)) before calling (.clearAllTabs())
Also this answer may help? (How to remove tab from TabHost)

I would suggest a different approach. You can use an ActivityGroup to build your own TabControl. As you are using normal Buttons (or similar controls just as you like) you can easyly arrange/create/remove them as needed.
I can't dump the whole code here but that is basically what I did when I had the same problem:
Create an Activity inherited from ActivityGroup
Place a ViewGroup in your layout where you want to show the sub-activities
Setup your buttons as needed (LinearLayout works fine with a variable count of buttons)
Start activites thru getLocalActivityManager().startActivity() as needed
You can now add/remove buttons as you like. The Activites follow the Android lifecycle so you don't have to delete them yourself.
You might have to implement onBackPressed on your ActivityGroup to properly handle the history but that depends on the project.

How to get TabHost

I am doing application with TabHost activity. I have 5 different class in that 4 class inserted into TabHost view. In one particular class i have list view with onItemclicklistener. while clicking the list view, it goes to different activity(ie 5th class). I want to place the clicked activity in TabHost. (ie) whenever i click the list view, the calling activity should appear in TabHost.But now it appears without tab host. i want to place Tab host in 5 th class by clicking listview. I dont know how to do this, if any one having idea pls let me know and guide me how to do this.

host= (TabHost)findViewById(android.R.id.tabhost);
host.setup();
TabHost.TabSpec spec;
// Create an Intent to launch the first Activity for the tab (to be reused)
Intent i = new Intent().setClass(this, library.class);
spec = host.newTabSpec ("FirstGroup").setIndicator("Library",getResources().getDrawable(R.drawable.imagename)).setContent(i);
host.addTab(spec);
u have to add your all activity like this(here Library)

Activity lifecycle within a tabwidget

I'm trying to notify my activity when the relevant tab is selected.
Consider the follwoing situation:
MainActivity:
// Create an Intent to launch an Activity for the tab (to be reused)
intent = new Intent().setClass(this, HomeActivity.class);
// Initialize a TabSpec for each tab and add it to the TabHost
spec = tabHost.newTabSpec("home").setIndicator("Home",
res.getDrawable(R.drawable.ic_tab_home))
.setContent(intent);
tabHost.addTab(spec);
// Do the same for the other tabs
intent = new Intent().setClass(this, ProceduresActivity.class);
spec = tabHost.newTabSpec("procedures").setIndicator("Procedures",
res.getDrawable(R.drawable.ic_tab_checklist))
.setContent(intent);
tabHost.addTab(spec);
Now, the first time my second tab is selected, the onCreate method of ProceduresActivity is called.
What I want to be alble to do is, within ProceduresActivity, to be notified whenever tab 1 and tab 2 (mine) are selected.
I tryed overriding onPause and onResume within ProceduresActivity however those are only called when the MainActivity is pasued / resumed and not when I switch tabs...
So in other words I want ProceduresActivity to do something whenever the user selects second tab, and not only the first time.
Can someone help me please?
Thanks, Luca.

Hmmm. This seems like it might be a little difficult (I'm not even sure it's possible) to achieve. There are two ways I can see that you could achieve the same results.
The first way is by have the first tab refresh it's data/information when the user goes back to it. This can be done in the onResume() and by adding a flag to it. Pretty simple.
If you need your activity to do something that will take some time, you can make an ActivityGroup. It's basically a controller for multiple activities. It starts them all at the same time and just chooses which one is shown at once. This means that (in your case) both activities would be running, but only one would be shown. When you want the first tab to do something while the user is using the second tab, you go to the ActivityGroup (which is like a controller) and tell it to do whatever you want with the first tab.
The only problem I see with the ActivityGroup route is binding it to your tabs, but there are many workarounds for this.

Maybe this can help you, i use this to perform an action when the tabs change. But maybe you can alter it to do a specific action with every tab?
getTabHost().setOnTabChangedListener(new OnTabChangeListener() {
public void onTabChanged(String tabId) {
//TODO, action to be performed
}
}
});

Force Tabhost to initiate Activity (refresh)

To put it simply. From a context menu on a TabActivity how can I initiate executing the intent for the current tab? I am trying to force a refresh.
The tabs all initiate activities displaying a subset of people names. While in one list you call up an edit activity which allows you to associate the name to one of the other lists in the TabHost. Using the back button to get back to the tabhost (onResume fires) and the list has not updated. I would like to have a context menu item to refresh the current tab.
I know about using one activity for all the views in a tabhost but for many reasons I have not chosen that method.

You can also try adding a flag to the intent when you set up the tabs in the first place.
Intent i = new Intent().setClass(this, YourClass.class)
.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
TabHost.TabSpec spec = tabHost.newTabSpec("name")
.setIndicator("Class",res.getDrawable(R.drawable.ic_tab_something))
.setContent(intent);
Tabhost tabHost.addTab(spec);

I think due to the activity lifecycle, you will have some problems 'restarting' the activity (Activity lifecycle - startActivity()) - if you were to move any logic you have inside the onCreate method into another method, then call the method from onCreate and onResume, so it rebuilds the tab content for you.
Alternatively you could add a menu item to call this method, so onCreate calls the logic method on first run, and your user can call it from the menu to refresh the contents.