Why setting "layout_width" of RelativeLayout to a fixed value in layout xml not working?

Question

I want to set the width and height of a RelativeLayout to a fixed value. My item_view.xml looks like this;

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="100dp"
    android:layout_height="100dp"
    android:orientation="vertical"
    android:background="#00ff00">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="abc"/>

</RelativeLayout>

Here is the activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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">

    <RelativeLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

    </RelativeLayout>

</android.support.constraint.ConstraintLayout>

And finally my generateView function in the MainActivity.java;

private void generateItemView()
{
    LayoutInflater layoutInflater = (LayoutInflater) getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View itemView = layoutInflater.inflate(R.layout.item_view, null);

    RelativeLayout containerView = findViewById(R.id.container);
    containerView.addView(itemView);
}

And this is the result;

As you can see, this is not 100dpX100dp size.

On the other hand, if I do this programmatically it works. Here is the updated generateView function;

private void generateItemView()
{
    LayoutInflater layoutInflater = (LayoutInflater) getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View itemView = layoutInflater.inflate(R.layout.item_view, null);

    int sizeDp = 100;
    DisplayMetrics displayMetrics = getResources().getDisplayMetrics();
    int sizePx = Math.round(sizeDp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT));

    RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(sizePx, sizePx);
    itemView.setLayoutParams(params);

    RelativeLayout containerView = findViewById(R.id.container);
    containerView.addView(itemView);
}

And it works just fine...

My question is, why can't we use the layout_width and layout_height properties in the layout xml file?

score 2 · Accepted Answer · answered Sep 25 '18 at 21:00

Your problem is in this line:

View itemView = layoutInflater.inflate(R.layout.item_view, null);

When you pass null as the parent, then any layout_ attributes will be ignored. In order to retain them and have them take effect, you must pass a parent.

View itemView = layoutInflater.inflate(R.layout.item_view, containerView, false);

Your IDE should warn you about this case:

score 0 · Answer 2 · answered Sep 25 '18 at 20:57

You probably need to set the parent in your call to layoutinflator.inflate: layoutinflator.inflate(R.layout.item_view, containerview, false);. You'll also need to re-arrange the code so this is run after you instantiate containerview.

For a more detailed answer on why this is happening, check out https://stackoverflow.com/a/5027921

Why setting "layout_width" of RelativeLayout to a fixed value in layout xml not working?

2 Answers2