Develop Reference

Should I create an activity for each screen?

I will start with an example... If you go to Settings > Applications > Manage applications, a new screen will open with a list of the installed applications: if you click on any application of the list, it will open a new screen containing information about the application.
Well, some settings of my application must be managed through a list, and this list should behave like the above example. I have already created a PreferenceActivity with some categories, each of which has some items: when I click on one of these items, I would like it to open a new screen where the new data is placed on a list, just like the list of the applications of the above example. Moreover, when I click on any entry of this list, it will open a new screen in order to set some data.
How should I proceed? Should I create an activity for each screen?

Android was created this way, according to the documentation "An activity is a single, focused thing that the user can do.", so yes, you should have an activity for each screen.
This changed a little with Honeycomb with the introduction of Fragments, but if you're not developing for tablets you should keep the one page, one activity mindset on Android.

Generally you have each activity call by another, the caller is pushed onto a stack (unless the calling activity ask's to be removed) and goes dormant until it returns
Basically you create an Intent in Activity A to start Activity B, you can pass data by using startActivityForResult with extras in the intents Example: How to pass data between activities
When you press the back button then that previous activity becomes active again and the result handler you set up can get any return data.
You might also look at fragments in the support API if you want to provide tablet support that looks and behaves better.

That is propably the best way to do it, at least if you're not working on a wizard style activity.
Use a ListActivity to show your list, and pass data to and from this activity using intents.

I was able to implement this at work, I don't remember right now in the head how I implemented it, was long time ago. If nobody has a good answer for you I will post it tomorrow, however: I remember putting a Preference, which will act as a button, then I added a preferenceClickListener in order to open a new PreferenceScreen on click.
But like I said, I'll post it for you tomorrow if you don't get a satisified answer.
Good luck!
UPDATE:
?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<PreferenceCategory
android:title="Personal"
android:key="personal_category">
<Preference
android:key="birth"
android:title="Birth"
android:summary="Choose your birthday"/>
<PreferenceScreen
android:key="height_imp"
android:title="Height"
android:summary="Enter your height">
<EditTextPreference
android:key="foot"
android:title="Foot"
android:summary="foot"
android:numeric="integer"
android:dialogTitle="Foot"/>
<EditTextPreference
android:key="inch"
android:title="Inch"
android:summary="inch"
android:numeric="integer"
android:dialogTitle="Inch"/>
</PreferenceScreen>
<EditTextPreference
android:key="weight"
android:title="Weight"
android:summary="Enter your weight"
android:numeric="integer"
android:dialogTitle="Weight"/>
</PreferenceCategory>
</PreferenceScreen>
That's it! When you click on it, it will take you to the second PreferenceScreen and so on, then finally when you need to customize your layout you'll need to open an Activity.
You could then use a Preference and add onPreferenceClick:
#Override
public boolean onPreferenceClick(Preference preference) {
if(preference == birth){
startActivity(new Intent(getBaseContext(), Birth.class));
}
if(preference == height_imp){
PreferenceScreen a = (PreferenceScreen) preference;
a.getDialog().getWindow().setBackgroundDrawable(new ColorDrawable(Color.WHITE));
return false;
}
return true;
}
If you need to change the background or something else with the preferenceScreen, then add a preferenceClickListener as well: height_imp = (PreferenceScreen)getPreferenceScreen().findPreference("height_imp");
height_imp.setOnPreferenceClickListener(this);

See... if once the user wants to return from certain point to previous position... if you had created a seperate activity for each of them... the present activity will be popped off the stack... letting the previous activity to be displayed...If you are changing the content of the list for every new screen...instead of creating new activity... then it will be difficult for the user to come back... you should again and again change the content of adapter..
So I think.. creating seperate activity for each screen is better..( and you can use same [any custom layout if you have]layout file for all activities..)

Providing my own list view for a prefrence activity

I have a class which extends from ListView. I added some extra functionality(drag and drop) for this new class. My question is there any way i can use this extended ListView class in a preference activity.
I need to provide drag and drop functionality for a legacy preference activity.

Are you asking if it's possible to open an arbitrary activity from a clicked item in a preference activity? If so, you need to do two things. First, add a PreferenceScreen item to your preferences xml file:
<PreferenceScreen
android:key="CUSTOM_ACTIVITY_KEY"
android:title="Title"
android:summary="Summary" />
Then in your settings activity's onCreate:
Preference pref = getPreferenceScreen().findPreference("CUSTOM_ACTIVITY_KEY");
final Intent intent = new Intent(this, CustomActivity.class);
if (pref != null)
{
pref.setOnPreferenceClickListener(new OnPreferenceClickListener()
{
public boolean onPreferenceClick(final Preference preference)
{
startActivity(intent);
return false;
}
});
}

If running a custom activity off of a PreferenceScreen item isn't enough, the only other option I could think of is to roll your own Preferences implementation. Someone else should correct me if I'm mistaken, but I think it might be possible to pull the Preferences source and modify accordingly.

I came across another API in
android.preference.PreferenceScreen.bind(ListView listView)
Binds a ListView to the preferences contained in this PreferenceScreen via getRootAdapter().
So after inflating the layout file, we will be able to attach the our custom listview to this the preferenceScreen of the activity.

How to Initialize Preferences Screen on First Invocation?

I believe I am correctly initializing preferences from XML. My Preferences Screen also works properly and reflects the correct user selected settings.
However, upon first invocation of that Preferences Screen, none of the settings are checked (checkbox) or selected (list). This, of course, confuses the user as it doesn't reflect the current (default/initial) value.
Since all I do to invoke the Preferences Screen is
startActivity(new Intent(this, EditPreferences.class));
And my EditPreferences class only contains:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.usersettings);
}
I am not sure where or how to tell it to pre-initialize the visual display with the default setting.
I have this hunch that all I am missing is a single line somewhere, but I don't know where: XML file? override a method in EditPreferences? Other?

Can't you define the default value in the XML itself?
<CheckBoxPreference ...
android:defaultValue="true"
... />

You can specify a default value on a preference (in your xml layout for example):
<EditTextPreference android:defaultValue="whatever" />

Is it possible to display a DialogPreference without showing a PreferenceScreen?

I'm currently writing a live wallpaper for Android and it has a PreferenceScreen which currently contains only one preference - a DialogPreference to set various properties of animation.
User workflow to configure it currently looks like this:
Settings... => (shows the preferences list with only one title ) Animation speed => MyDialogPreference
What I want is to make the workflow like this:
Settings... => MyDialogPreference
I.e. I'm looking for a way to skip showing that preferences list with only one item and to show that dialog right away.
But it seems that PreferenceActivity requests itself to have PreferenceScreen as a root element of preference hierarchy. So... is it even possible to do what i want? :)
Code references:
Activity code:
public class ForestLakePreferences extends PreferenceActivity
{
protected void onCreate(Bundle savedState)
{
super.onCreate(savedState);
getPreferenceManager().setSharedPreferencesName(
ForestLakeWallpaper.PREFS_NAME);
addPreferencesFromResource(R.xml.preferences);
}
}
Prefs resource:
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
xmlns:android="http://schemas.android.com/apk/res/android"
android:key="lake_preferences">
<DurationEditDialog
android:title="#string/prefs_duration_title"
android:dialogTitle="#string/configure_durations_dlg_title"
android:dialogLayout="#xml/set_durations_layout" />
</PreferenceScreen>

It turned out this can't be done in that way.
But i've found a workaround: i made my activity not a PreferencesActivity, but a custom one and made it look like dialog by placing the following in AndroidManifest.xml
<activity android:theme="#android:style/Theme.Dialog" .... />

A DialogPreference has a showDialog(Bundle state) method, try calling it. I am not sure if you will have to give it anything else like the Preferences or anything.

Going from a PreferenceScreen to a DialogPreference

My application has a setting menu which is actually a PreferenceActivity.
When it's created, if a boolean value is not set I want to go to the DialogPreference which sets that.
I tried doing it with an intent but the application force closed with this error msg:
E/AndroidRuntime( 239):
android.content.ActivityNotFoundException:
Unable to find explicit activity class
{com.xxxx/com.xxxx.xxxxPreference};
have you declared this activity in
your AndroidManifest.xml?
How should I do this? It's ok to add that DialogPreference to the manifest?

A DialogPreference isn't an Activity in its own right. It's just a Preference which displays a Dialog when clicked.
The problem is that there's no obvious way programmatically click a Preference. However, since you're using DialogPreference you've already got you own subclass of it. So we can solve our problem by adding the following method to your subclass of DialogPreference:
//Expose the protected onClick method
void show() {
onClick();
}
Then in the onCreate() of your PreferencesActivity you'll have something like this to load the preferences from your XML file:
// Load the preferences from an XML resource
addPreferencesFromResource(R.xml.preferences);
After that you can put some code like this:
booleanProp = true; //set this to the value of the property you're checking
if (! booleanProp) {
//Find the Preference via its android:key
//MyDialogPreference is your subclasss of DialogPreference
MyDialogPreference dp = (MyDialogPreference)getPreferenceScreen().findPreference("dialog_preference");
dp.show();
}
This is a bit of hack, as exposing protected methods isn't ideal, but it does work.
Another option would be to replace the Dialog with a PrefenceActivity which contained all the options you wish to maintain and then you could launch it via an Intent, but I'm assuming there's a good reason that you want your own custom Dialog with a specific layout. If you do want a second PreferenceActivity you can add it to your preferences XML file as follows:
<PreferenceScreen
android:title="#string/title_of_preference"
android:summary="#string/summary_of_preference">
<intent android:action="your.action.goes.HERE"/>
</PreferenceScreen>

To start an activity with an Intent, the activity must be in the Android manifest. Just add a line like:
<activity android:name=".path.to.MyActivity"/>