Develop Reference

Starting a new FragmentActivity without content view shows non-transparent view

I open this simple fragmentActivity without setting any contentView
public class InternalDummyActivity extends FragmentActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//
}
}
But I still see a blank view is opened. Why is that?
I have thought if there is no setContentView then the activity is transparent.
is it because of the fragmentActivity? How do I create a transparent fragmentActivity then?

Instantiate a custom activity class with a ListView object from MainActivity

Unlike typical android projects starting with MainActivity with all the code of the layout object in it. This architecture requires me to have the initial code in a custom object. Here's a structure for better understanding.
java/MainActivity.java
java/User.java
layout/activity_main.xml
layout/user.xml
Now I also need a reference to User object within MainActivity and it looks like this.
public class MainActivity extends AppCompatActivity {
public Users users; // instantiate custom class and show
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
My User class looks like this.
public class User extends AppCompatActivity {
ListView userList;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.user_list, container, false); // Inflate the layout for this fragment
userList = view.findViewById(R.id.userList);
return view;
}
}
layout/user.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="org.puremvc.java.demos.android.employeeadmin.view.components.UserList">
<ListView
android:id="#+id/userList"
android:layout_width="395dp"
android:layout_height="715dp"
tools:layout_editor_absoluteX="8dp"
tools:layout_editor_absoluteY="8dp" />
</FrameLayout>
So, in other words, MainActivity just acts like a stage doing nothing except just providing a reference to the Initial object. Now I do need MainActivity to be there, can't point User to be a launcher in the manifest. Responsibilities are to be taken care of by User class.
Question: How to instantiate CustomClass User and show.
Context: The MainActivity class has to be minimalistic and clean, no User related code (ListView), all logic lies in the custom class.
P.S. There can be lateral approaches, as long as I have a reference to user Object in MainActivity and it's displayed on launch, I'll accept the answer.

As per my understanding: there should be two approaches.
First, by using the Fragment inside your Activity. Write all initialize and data flow codes inside the fragment and just initialize and start the fragment from the Activity. So when the Activity will start, it will give all its tasks to the fragment with its Context and rest thing Fragment will do.
Like below:
public class MainActivity extends AppCompatActivity {
public Users users; // instantiate custom class and show
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//the fragment stuff
FragmentManager fm= getFragmentManager() //or get SupportFragmentManager when the Fragment comes from Support lib
FragmentTransaction ft= fm.beginTransaction();
Fragment fragment= new UserListFragment();
ft.add(R.id.fragment_container, fragment);
ft.commit();
}
}
OR, the second approach should by using Interface and communicate both Activity and the Custom Class (or you can call it Controller) with it.
Its nothing, but a simple MVC design pattern which I never recommend.
You can write one Interface like below:
public interface IController{
public void initialize(Activity activity, Bundle savedInstanceState);
public void engage();
public void disengage();
}
Then, make an instance of this Controller inside your Activity/BaseActivity and use like below:
public MainActivity(IController controller){
this.controller = controller;
}
Then call each callback methods from their appropriate place to make them work inside the Controller.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//give the priviledge of onCreate to initialize
controller.initialize(this, savedInstanceState);
}
Then in your Controller class, just write the same program which you supposed to write inside Activity:
public class Your_Controller implements IController {
#Override
public void initialize(Activity activity, Bundle savedInstanceState) {
//do super where needed
//make one class level Activity instance to work in other methods
act = activity;
//just initialize views like below
TextView tv = (TextView) activity.findViewById(R.id.abc);
}

Android custom reusable controls?

I have a few activities in an app I'm writing that I want to put a form on the page. It's the same form for all the activities that does the same except for different title and text.
Instead of rewriting the controls and the logic for each activities I'm looking for a way to create my own control that I can put in my layout xml files with my own properties so all I'll need to do is write it once and use that control where I need to.
how can I do such a thing?
Thanks

What about writing your control as an android Fragment? In the xml you can declare a FrameLayout and then insert the fragment inside it using the replace() method of FragmentTransaction.

You can use an Activity which extends android.app.Activity and define it the common logic.Then all your other activities will extend it in place of extending android.app.Activity. Then they will inherit it , and you can override what you want to Override as well.
This solution is not bad if you have exactly the same layout and just some differences, you can load the layout.xml only once and then use it in the child class as you like.
SuperClass :
public SuperClass extends Activity{
protected TextView myTextView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.my_layout);
myTextView = (TextView) findViewById(R.id.my_text_view);
}
}
ChildClassA :
public ChildClassA extends SuperClass {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.my_layout);
myTextView.setText("I am in A");
}
}
ChildClassB :
public ChildClassB extends SuperClass {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.my_layout);
myTextView.setText("I am in B");
}
}
Other suggestion:
Another idea is to create a custom view. see this tutorial also.

Depends on what differences you have in each Activity and how you access them.
If it's only some strings, that are different, put those strings inside the Intent, which starts the Activities and grab them in onCreate().
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.lyt_template_form);
((TextView) findViewById(R.id.txt_form_headline)).setText(getIntent().getStringExtra("headline");
((TextView) findViewById(R.id.txt_form_subtitle1)).setText(getIntent().getStringExtra("subtitle1");
//etc...
If there are more differences in your control code and you need to distinguish some kind of "Form Type A", "Form Type B", etc., you can put an indicator inside your Intent and check for that to make different decisions in your code.
So e.g.
if (getArguments().getInt("Type") == 0) {
// do stuff in control like this
} else if (getArguments().getInt("Type") == 1) {
// do stuff in control like this
// etc.
getArgument() is the equivalent of getIntent().getXyzExtra()

PreferenceFragment not showing properly

I am using PreferenceFragment to get preferences from user. I have designed a simple preference file having only one EditPreference. I have created the following preferencefragement file
public class fragact extends PreferenceFragment
{
#Override
public void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.fragpref);
}
}
In my main activity i am trying to show the fragment at the click of a button.However the fragment comes transparent and is not very visible and the underlying screen is seen through it.
why the fragment does not come proper. i created another activity and used it to show the fragment.it worked properly .but why can we show the fragment directly rather than showing through another activity in its oncreate and calling it through startActivity in class fragprefmain.
public class fragprefmain extends Activity
{
EditText et;
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.fragpref);
et=(EditText)findViewById(R.id.editText1);
}
public void showp(View v)
{
FragmentManager fm=getFragmentManager();
FragmentTransaction ft=fm.beginTransaction();
ft.replace(android.R.id.content, new fragact());
ft.commit();
}
public void showval(View v)
{
SharedPreferences sp=PreferenceManager.getDefaultSharedPreferences(this);
et.setText(sp.getString("ekey", "no valued given"));
}

maybe try to replace the opaque id
android.R.id.content
with your own layout id that you define in your activity xml file
it can be an empty layout but you must give the layout an id, say:
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="#+id/my_layout_id">
so now you get:
.replace/add(R.id.my_layout_id, new fragact());

You might as well create a preferenceActivity as given by WannaGetHigh in How do you create Preference Activity and Preference Fragment on Android?

findViewById() returns null

There are a few questions already asking about this, but I'm not finding a solution. I have a LiveWallpaper that is using its own subclass of PreferenceFragment to specify preferences. The solution most often cited is to assure that setContentView() is called before findViewByID(). I am not calling setContentView() at all because I do not have a layout specified. This app originally implemented the preferences using the deprecated methods like PreferenceActivity.getPreferenceManager() and without using a layout and worked just fine. I am trying to bring the code up-to-date in using PreferenceFragment.
Am I required to have a layout and if so, what would I have when I don't really want one?
Or is there a another way to get/set the View?
public class SetPreferenceActivity extends Activity {
private CheckBox redCheckBox;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.main); ???
redCheckBox = (CheckBox)findViewById(R.id.redCheckBox); // returns null
getFragmentManager().beginTransaction().replace(android.R.id.content, new LiveWallpaperPreferenceFragment()).commit();
}
}

You can create views dynamically :
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView textView = new TextView(this);
textView.setText("Hello");
setContentView(textView);//<----set the view !
}
}