Develop Reference

Custom view: how to set the root layout

I am trying to create a custom view (which extends RelativeLayout), which wraps a lot of other views.
I would like to create that child-views in a xml layout file. Now I wonder how I could inflate that layout and use it in my custom view. Something like this would be great (inside my custom view):
RelativeLayout rootLayout = (RelativeLayout) inflater.inflate(my xml file)
this.setContenView(rootLayout);
Unfortunatelly this is only possible in activities. Is there something similar for views?
EDIT:
I don't want to use View.addView(rootLayout) cause that adds another view hierachy, which is not needed.

You could try to use the <merge> tag as the root element in your layout and inflate it in your custom RelativeLayout with this as the parent and attachToRoot set to true. You do not have to call addView then.
Here is a similar example with a LinearLayout (bottom of page), should work with RelativeLayout too.

Use the below
View v =getLayoutInflater().inflate(R.layout.mylayout,null);
// inflate mylayout.xml with other views
CustomRelativeLayout cs = new CustomRelativeLayout(this);
// CustomRelativeLayout is a class that extends RelativeLayout
cs.addView(v); // add the view to relative layout
setContentView(cs); // set the custom relative layout to activity
Example :
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="111dp"
android:text="TextView" />
</RelativeLayout>
SView
public class SView extends RelativeLayout {
Paint p,paint;
public SView(Context context) {
super(context);
TextView tv = new TextView(context);
tv.setText("hello");
this.addView(tv);
}
}
In MainActivtiy
View v =getLayoutInflater().inflate(R.layout.mylayout,null);
SView cs = new SView(this);
cs.addView(v);
setContentView(cs);
Snap
Edit:
If you wish to inflate in CustomRelative layout
In the constructor
LayoutInflater inflater = LayoutInflater.from(context);
View v =inflater.inflate(R.layout.mylayout,null);
TextView tv = new TextView(context);
tv.setText("hello");
this.addView(tv);
this.addView(v);

Within your view you can get layout inflater from the context, inflate children and add them to this (sub-class of RelativeLayout)
final LayoutInflater inflater = (LayoutInflater) this.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
final View child = inflater.inflate(R.layout.custom_layout, this, false);
// Then add child to this (subclass of RelativeLayout)
this.addView(child);
Edit:
The code above shows how to inflate children inside a custom view.
This link shows how to insert the custom view itself into XML layout.

Why do I keep getting a null reference to my LinearLayout?

I have a layout called view.xml which contains a View called view_related. Basically, in my dictionary app, if there are related words to an entry, I will replace view_related with a LinearLayout that contains a header "Related entries" and a bunch of TextViews representing every related word.
I keep getting a NullPointerException everytime I'm adding a TextView to the LinearLayout in my Activity's onCreate() method, and I don't understand why though my code looks pretty straightforward.
view.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView android:id="#+id/view_header"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="12pt"
android:textColor="#fff"
android:textStyle="bold"
android:background="#990011"
android:padding="10dp"
android:text="lalala word"
/>
<ScrollView android:id="#+id/view_description"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="#id/view_header">
<LinearLayout android:id="#+id/view_description_content"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="20dp"
android:text="#string/demo_definition"
/>
<!-- THIS WILL BE REPLACED -->
<View android:id="#+id/view_related"
android:layout_width="match_parent"
android:layout_height="wrap_content"></View>
</LinearLayout>
</ScrollView>
</RelativeLayout>
view_related.xml, the LinearLayout that will replace the View element in view.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/view_related_entries"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView android:id="#+id/view_related_header"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="5dp"
android:textColor="#fff"
android:textStyle="bold"
android:textSize="7pt"
android:background="#000"
android:text="Related entries"
/>
<LinearLayout android:id="#+id/view_related_list"
android:layout_width="match_parent"
android:layout_height="wrap_content"
>
</LinearLayout>
</LinearLayout>
And finally, the onCreate method, which for now assumes the related entries are "Hello" and "Goodbye:"
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view);
LinearLayout ll = (LinearLayout) findViewById(R.id.view_related_list);
TextView tv = new TextView(this);
tv.setText("Hello");
ll.addView(tv); // NULL POINTER EXCEPTION
tv = new TextView(this);
tv.setText("Goodbye");
ll.addView(tv);
LayoutInflater li = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
View view = findViewById(R.id.view_related);
ViewGroup parent = (ViewGroup) view.getParent();
int index = parent.indexOfChild(view);
parent.removeView(view);
View llview = li.inflate(R.id.view_related_entries, parent, false);
parent.addView(llview, index);
}

setContentView(R.layout.view);
LinearLayout ll = (LinearLayout) findViewById(R.id.view_related_list);
The function findViewById only finds views that are actually set. Your current setContentView does not set an xml that has the id you are looking for in it, so the first line I quoted will not result in anything.
You should either load the correct XML, or inflate the view you are looking for with an inflater

the line (LinearLayout ll = (LinearLayout) findViewById(R.id.view_related_list);) will search for view_related_list in view.xml, as in the line before that is the view you are using..
You need to inflate view_related.xml first and then get the view from it..

You're doing a lot of wrong things in your code. First you search for a LinearLayout that isn't in the current layout and also isn't in any inflated layout at that moment. Second, you try to inflate an id reference instead of a layout reference. Last, you should use another approach for what you're trying to do. Your code should be(from what I understood):
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view);
LayoutInflater li = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);
View view = findViewById(R.id.view_related);
ViewGroup parent = (ViewGroup) view.getParent();
int index = parent.indexOfChild(view);
parent.removeView(view);
View llview = li.inflate(R.layout.view_related, parent, false); // is view_related the name of the extra layout file?
parent.addView(llview, index);
LinearLayout ll = (LinearLayout) findViewById(R.id.view_related_list); // or search for it in llview, llview.findViewById(R.id.view_related_list);
TextView tv = new TextView(this);
tv.setText("Hello");
ll.addView(tv); // NULL POINTER EXCEPTION
tv = new TextView(this);
tv.setText("Goodbye");
ll.addView(tv);
}
This is a situation when you should use a ViewStub to add the new layout file. Although, I don't understand why don't you add the new layout file directly in the view.xml if you're going to add the layout's content in the onCreate method.

i think you need to use setContentView(R.layout.view_related); instead of setContentView(R.layout.view);
or another simple thing you can do is take the linear layout in the same layout "view" and make it invisible when not required and visible when required

You may forgetting to declare your Activity in manifest.xml

Adding multiple child views to parent view

I have a LinearLayout view element inside a ScrollView (main.xml):
<ScrollView ...>
<LinearLayout
android:id="#+id/root"
android:orientation="vertical"
>
<TextView .../>
<EditText .../>
...
</LinearLayout>
</ScrollView>
As you see above, there are also some other elements inside the root LinearLayout .
Now, I would like to programmatically(dynamically) add more views to the LinearLayout (id="root").
I tried the following way to add more child views to this root:
Firstly, I created my child view which is in a separate layout file:
child.xml
<LinearLayout
android:id="#+id/child"
>
<TextView id="mytxt"... />
<ListView id="mylist".../>
</LinearLayout>
Secondly, I inflate & get two instances of above child view, initialize elements inside:
/***inflate 1st child, initialize its elements***/
LinearLayout child_1 = (LinearLayout) inflater.inflate(R.layout.child, null);
TextView txt1 = (TextView)child_1.findViewById(R.id.mytxt);
txt1.setText("CAR");
ListView list1 = (ListView)child_1.findViewById(R.id.mylist);
// Code to initialize 'list1' (I did not paste code here)
/*** inflate 2nd child, initialize its elements ****/
LinearLayout child_2 = (LinearLayout) inflater.inflate(R.layout.child, null);
TextView txt2 = (TextView)child_2.findViewById(R.id.mytxt);
txt2.setText("PLANE");
ListView list2 = (ListView)child_2.findViewById(R.id.mylist);
// Code to initialize 'list2' (I did not paste code here)
Finally, I add them to root LinearLayout:
//get root
View contentView = inflater.inflate(R.layout.main, null);
LinearLayout root = (LinearLayout) contentView.findViewById(R.id.root);
//add child views
root.add(child_1);
root.add(child_2);
When I run my app on device, I can only see child_2 layout without seeing child_1 under 'root', why??

in LinearLayout default orientation is horizontal set it vertical.......
from
http://developer.android.com/reference/android/widget/LinearLayout.html
see
The default orientation is horizontal.
and you set text in txt1.setText("PLANE"); set in txt2.setText("PLANE");
both text set in same textview.....
txt1.setText("CAR");
txt1.setText("PLANE");

How do you create your layout? Do you do it through setContentView(int)? Then you should retrieve that instance by doing this in your activity:
findViewById(R.id.root);

How do I add elements dynamically to a view created with XML

I'm trying to add dynamic content to a view that has been created with XML.
I have a view "profile_list" that has a ScrollView that I like to add some elements to.
Here is some code of what I'm trying to do.
// Find the ScrollView
ScrollView sv = (ScrollView) this.findViewById(R.id.scrollView1);
// Create a LinearLayout element
LinearLayout ll = new LinearLayout(this);
ll.setOrientation(LinearLayout.VERTICAL);
// Add text
tv = new TextView(this);
tv.setText("my text");
ll.addView(tv);
// Add the LinearLayout element to the ScrollView
sv.addView(ll);
// Display the view
setContentView(R.layout.profile_list);
The plan is to add a TableLayout and fill it dynamically and not just a dummy text but first I must get this to work.
Any help is welcome.
Kind Regards
Olle
I found the solution!
Stupid me I had left a element in my ScrollView in my XML-file!
Anyway her is a working example:
LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = inflater.inflate(R.layout.profile_list, null);
// Find the ScrollView
ScrollView sv = (ScrollView) v.findViewById(R.id.scrollView1);
// Create a LinearLayout element
LinearLayout ll = new LinearLayout(this);
ll.setOrientation(LinearLayout.VERTICAL);
// Add text
TextView tv = new TextView(this);
tv.setText("my text");
ll.addView(tv);
// Add the LinearLayout element to the ScrollView
sv.addView(ll);
// Display the view
setContentView(v);
And the XML-file to match
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ScrollView
android:id="#+id/scrollView1"
android:clickable="true"
android:layout_weight="1"
android:layout_width="fill_parent"
android:layout_marginBottom="50px"
android:layout_height="fill_parent">
</ScrollView>
</LinearLayout>
Hope this will help someone. Thanks for all help!

The way that you are adding things to the view is basically right - you just get the container object by its ID and then add them.
It looks like you are setting the content view to be the wrong view though. You should inflate the view, add the children and set it as the content view, or set the content view from a resource ID then do the manipulation. What you are doing is manipulating a view and then adding a different one. Try moving your setContentView(...) to the start of the block.

How to add a button control to an android xml view at runtime?

I have an android xml layout, main.xml. I would like to add controls to this layout at runtime (I would like to add a series of additional linear layouts that contain buttons controls). Can I do that and if yes, how?
Thanks

I see the error u r doing here
LinearLayout mainLayout = (LinearLayout) findViewById(R.layout.main);
You r taking the layout as Linearlayout object, you should take the LinearLayout id
Try this
LinearLayout lnr = (LinearLayout) findViewById(R.id.LinearLayout01);
Button b1 = new Button(this);
b1.setText("Btn");
lnr.addView(b1);

You can add controls programmatically if you want in your code, or even another XML with a View and an Inflater.
Here you can read the basics: http://developer.android.com/guide/topics/ui/declaring-layout.html

Ok, I have got it to work.
The steps are the following:
First inflate the xml layout, ie,
View view = View.inflate(this, R.layout.main, null);
Then instantiate the container object from the xml layout into a ViewGroup class, ie,
ViewGroup container = (ViewGroup) view.findViewById(R.id.myContainer);
Then create a linearLayout object, create and add onto that any controls needed, add the linearLayout to the container object and use setContentView on the view object, ie,
container.addView(buttonsLayout);
this.setContentView(view);

You can do this quite easy by setting an id on the layout on which you want to add views to. Say your main.xml look like this:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView android:id="#+id/label"
android:layout_width="fill_parent"/>
<LinearLayout android:id="#+id/container"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
</LinearLayout>
</LinearLayout>
Lets assume that you want to add your additional views to the LinearLayout with id id/container. In your onCreate method you could retrieve that object for later use:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mContainer = (ViewGroup)view.findViewById(R.id.container);
}
Now you are all set to add other views to your container ViewGroup:
LinearLayout theButtons = getButtons()
mContainer.addView(theButtons);
In the getButtons method you need to create your LinearLayout containing the buttons you need. Either you do this programmatically or by inflating a view defined in an XML file. See LayoutInflater.inflate.

just try this:
LinearLayout mainLinearLayout = (LinearLayout) findViewById(R.layout.llmain);
now create button dynamically like this
Button btn1 = new Button(this);
btn1.setText=("Button 1");
mainLinearLayout .addView(btn1);
now if you want to add onether linearlayout then add it below button then
LinearLayout llinner = new LinearLayout(this);
Button btn2 = new Button(this);
btn2.setText=("Button 2");
mainLinearLayout .addView(btn2);
llinner.addView(btn2 );
mainLinearLayout .addView(llinner);

Try this :
LinearLayout ll =(LinearLayout)findViewById(R.id.linlay);
Button b = new Button(this);
b.setText("Hello");
l.addView(b);
This might help you

Here is what I did to display a set of runtime buttons on table layout.
MainActivity.java
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
View view = View.inflate(this, R.layout.activity_main, null);
TableRow myrow = (TableRow) view.findViewById(R.id.myrow);
Button btn1 = new Button(this);
btn1.setText("Button 1");
myrow .addView(btn1);
Button btn2 = new Button(this);
btn2.setText("Button 2");
myrow .addView(btn2);
this.setContentView(view);
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ScrollView
android:id="#+id/myview"
android:layout_width="404dp"
android:layout_height="691dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<TableLayout
android:id="#+id/mylayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TableRow android:id="#+id/myrow"></TableRow>
</TableLayout>
</ScrollView>
</androidx.constraintlayout.widget.ConstraintLayout>
AVD Pixel4API30
Output screenshot