How layoutinflator works at runtime

Shubham Agarwal

14 December 2016

There is common issue that people including me faces. The issue is why does LayoutInflater ignore the layout parameters that I’ve specified?

E.g. why are the layout_width and layout_height values from my resources XML not honored?

The following tutorials shows how to dynamically populate a layout using LayoutInflater.

Before we get started see what LayoutInflater.inflate() parameters look like:

resource: ID for an XML layout resource to load (e.g., R.layout.main_page)
root: Optional view to be the parent of the generated hierarchy (if attachToRoot is true), or else simply an object that provides a set of LayoutParams values for root of the returned hierarchy (if attachToRoot is false.)
attachToRoot: Whether the inflated hierarchy should be attached to the root parameter? If false, root is only used to create the correct subclass of LayoutParams for the root view in the XML.
Returns: The root View of the inflated hierarchy. If root was supplied and attachToRoot is true, this is root; otherwise it is the root of the inflated XML file.

Now for the sample layout and code.

Main layout (main.xml):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:id="@+id/container"

android:layout_width="match_parent"

android:layout_height="match_parent">

</LinearLayout>

Added into this container is a separate TextView, visible as small red square if layout parameters are successfully applied from XML (red.xml):

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="25dp"
    android:layout_height="25dp"
    android:background="#ff0000"
    android:text="red" />

<?xml version="1.0" encoding="utf-8"?>

<TextView xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="25dp"

android:layout_height="25dp"

android:background="#ff0000"

android:text="red" />

Now LayoutInflater is used with several variations of call parameters

public class InflaterTest extends Activity {

    private View view;

    @Override
    public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);

      setContentView(R.layout.main);
      ViewGroup parent = (ViewGroup) findViewById(R.id.container);

      // result: layout_height=wrap_content layout_width=match_parent
      view = LayoutInflater.from(this).inflate(R.layout.red, null);
      parent.addView(view);

      // result: layout_height=100 layout_width=100
      view = LayoutInflater.from(this).inflate(R.layout.red, null);
      parent.addView(view, 100, 100);

      // result: layout_height=25dp layout_width=25dp
      // view=textView due to attachRoot=false
      view = LayoutInflater.from(this).inflate(R.layout.red, parent, false);
      parent.addView(view);

      // result: layout_height=25dp layout_width=25dp 
      // parent.addView not necessary as this is already done by attachRoot=true
      // view=root due to parent supplied as hierarchy root and attachRoot=true
      view = LayoutInflater.from(this).inflate(R.layout.red, parent, true);
    }
}

public class InflaterTest extends Activity {

private View view;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

ViewGroup parent = (ViewGroup) findViewById(R.id.container);

// result: layout_height=wrap_content layout_width=match_parent

view = LayoutInflater.from(this).inflate(R.layout.red, null);

parent.addView(view);

// result: layout_height=100 layout_width=100

view = LayoutInflater.from(this).inflate(R.layout.red, null);

parent.addView(view, 100, 100);

// result: layout_height=25dp layout_width=25dp

// view=textView due to attachRoot=false

view = LayoutInflater.from(this).inflate(R.layout.red, parent, false);

parent.addView(view);

// result: layout_height=25dp layout_width=25dp

// parent.addView not necessary as this is already done by attachRoot=true

// view=root due to parent supplied as hierarchy root and attachRoot=true

view = LayoutInflater.from(this).inflate(R.layout.red, parent, true);

}

The actual results of the parameter variations are documented in the code.

SYNOPSIS: Calling LayoutInflater without specifying root leads to inflate call ignoring the layout parameters from the XML. Calling inflate with root not equal null and attachRoot=truedoes load the layout parameters, but returns the root object again, which prevents further layout changes to the loaded object (unless you can find it using findViewById()). The calling convention you most likely would like to use is therefore this one:

loadedView = LayoutInflater.from(context)
                .inflate(R.layout.layout_to_load, parent, false);

1 2	loadedView = LayoutInflater.from(context) .inflate(R.layout.layout_to_load, parent, false);