Develop Reference

How to inflate a costum-view on a view

I got an custom class. Which works great.
public class FocusGameView extends SurfaceView implements Runnable
At the activity itself I want to put the 'FocusGameView' on a view that I already created on the xml file.
so I tried to use the 'inflate' like this:
public class FocusGame extends Activity {
FocusGameView fgv;
View v;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
fgv= new FocusGameView(this);
v=(View) findViewById(R.id.frame_focus_game);
LayoutInflater mInflater;
mInflater = LayoutInflater.from(fgv.getContext());
v = mInflater.inflate(R.layout.activity_focus_game, null);
setContentView(R.layout.activity_focus_game);
}
The result of this code is opening the activity and set the layout. without put the custom view on the view itself.
I really hope you could help me with that.
Thanks in advance;
Yaniv.

You can only add a view to a view group, not a view, so lets image your View v is a RelativeLayout:
public class FocusGame extends Activity {
FocusGameView fgv;
RelativeLayout v;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_focus_game);
v=(View)findViewById(R.id.frame_focus_game);
fgv= new FocusGameView(this);
v.addView(fgv); //You only need to add the view to a parent to make it appear
}

Which lifecycle method will be invoked when Activity is showing?

Sometimes I need to do some operations(e.g. changing layout) when the activity is just showing. What I do now is using post():
public class MyActivity extends Activity {
#Override
public void onCreate() {
...
container.post(new Runnable(){
resize(container);
});
}
}
Is there any lifecycle method like onCreate can be used to simplify the code, that I don't need to call post?
#Override
public void onX() {
resize(container);
}

I think you mean do something after the UI is displayed.
Using a global layout listener has always worked well for me. It has the advantage of being able to remeasure things if the layout is changed, e.g. if something is set to View.GONE or child views are added/removed.
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// inflate your main layout here (use RelativeLayout or whatever your root ViewGroup type is
LinearLayout mainLayout = (LinearLayout ) this.getLayoutInflater().inflate(R.layout.main, null);
// set a global layout listener which will be called when the layout pass is completed and the view is drawn
mainLayout.getViewTreeObserver().addOnGlobalLayoutListener(
new ViewTreeObserver.OnGlobalLayoutListener() {
public void onGlobalLayout() {
// at this point, the UI is fully displayed
}
}
);
setContentView(mainLayout);
http://developer.android.com/reference/android/view/ViewTreeObserver.OnGlobalLayoutListener.html

Android: How to get a view given an activity inside a normal class?

I have a normal class (not an activity). Inside that class, I have a reference to an activity.
Now I want to access a view (to add a child) contained in the layout xml of that activity.
I don't know the name of the layout file of that activity. I only know the ID of the view, which I want to access (for example: R.id.my_view).
How can I do that?

Regarding the NullPointerException (which you should add to the question), always make sure you've called setContentView() in your Activity before trying to access a View defined in XML. Example usage:
public class MainActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
...
}
...
}
Then, somewhere,
ViewGroup group = (ViewGroup) context.findViewById(R.id.group); // In your example, R.id.my_view
The reason you need to have called setContentView() is that before it's called, your View(Group) doesn't exist. Because findViewById() is unable to find something that doesn't exist, it returns null.

As simple as that!
View view = activity.findViewById(R.id.my_view);
In case of the Layout:
LinearLayout layout = (LinearLayout) activity.findViewById(R.id.my_layoutId);
And to add the Views:
layout.addView(view);

You could make your method accept an Activity parameter and then use it to find the view by id.
Ex:
public class MyClass{
public void doSomething(Activity context){
TextView text=(TextView)context.findViewById(R.id.my_textview);
}
}
Then in your activity:
obj.doSomething(YourActivity.this);

Get access to Views in another layouts

How can I get reference to the TextViews, for example, if I didn't set layout as a content view?
I'm using TabHost to switch between Activities:
public class TimerResultsActivity extends TabActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
initTabs();
TextView resultsText = (TextView)findViewById(R.id.textView1);
resultsText.setText("test");
}
...
"textView1" has added to one of tabs, but hasn't declared in the main.xml.
How can I change a text on it?

You'll need a reference to the base of the layout that it is declared in. Then you can use the findViewById() method of the ViewGroup it belongs to.
TextView resultsText = (TextView)myTab.findViewById(R.id.textView1);
...

creating a xml layout from a custom layout. is it possible?

MainActivity.java:
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setTitle(R.string.app_name);
setContentView(new SampleView(this));
}
}
SampleView.java:
public class SampleView extends View {
#Override
protected void onDraw(Canvas canvas) {
if (certaincondition = true) {
//add elements to canvas etc
} else {
//How do I do the below? The layout is defined in xml.
//I do not want to use Intent. Please help me
//create a layout from resource R.layout.idAbout and transfer control.
}
}
}

Use a layout inflater:
View newRootViewElement;
LayoutInflater li = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
newRootViewElement= li.inflate(R.layout.idAbout, null);

You can inflate a layout using
View.inflate(getContext(), R.layout.idAbout, viewParent);
where viewParent is a ViewParent that will be the parent of the inflated view (and can be null).
But what are you trying to do? It's more than a little odd to start a new activity or to modify the view hierarchy from within onDraw(). You might want to post a runnable to a Handler that will do what you want on the next cycle of the event loop. To start a new activity (such as displaying “About” info for the app) you should take a look at the Intent class.