Android how to create simple custom UI elements

Use a TextView. The light bulb can be a left compound drawable. Set the background to a rounded rectangle shape drawable. This can all be specified in XML. See TextView.

This can also be accomplished with a LayerList drawable if text is not wanted. (The TextView solution also works without text - just set the text to "" or null.)

<layer-list>
    <item>
        <shape android:shape="rectangle">
            <corners android:radius="5dp" />
            <solid android:color="#FF9800" />
        </shape>
    </item>
    <item
        android:drawable="@drawable/ic_baseline_lightbulb_24"
        android:width="48dp"
        android:height="48dp"
        android:gravity="left|center_vertical" />
</layer-list>

The layer list is set as a background to a simple View.

<View
    android:layout_width="250dp"
    android:layout_height="56dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="16dp"
    android:layout_marginEnd="16dp"
    android:layout_marginBottom="16dp"
    android:background="@drawable/light_bulb_layer_list" />

To create the View in code:

View view = new View(context);
view.setLayoutParams(new ViewGroup.LayoutParams(width, height));
Drawable dr = ContextCompat.getDrawable(context,R.drawable.light_bulb_layer_list)
view.setBackground(dr);

Sure thing.

In this case a simple xml file like so would suffice. Let's name it something.xml inside the layout folder.

<LinearLayout ...>
  <ImageView ...>
</LinearLayout>

In another layout xml file you may just:

<ConstraintLayout ...>
  <include android:id="@+id/something"" layout="@layout/something" android:layout_width="70dp">
</ConstraintLayout>

See Reusing layouts

If you'd like to get a children you can always get them by using findViewById on your Activity or Fragment. If you're using Databinding or Viewbinding it just gets better: They'll appear as fields in the XBinding class that was generated out of the XML file

Hi VanessaF, going a little bit further with the clarifications you asked in the comments:

<include />

The <include /> tag is a special XML tag that we can use in our Android XML layout files to indicate that where we placed the <include/> we'd like it to be replaced by some other XML determined via the layout attribute inside the <include /> tag.

Here's an example:

Considering layout/example.xml

<TextView
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:text="Hello!"/>

And considering layout/parent.xml

<LinearLayout 
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="vertical">

  <Button .../>
  <include layout="@layout/example"/>
  <ImageView android:drawable="@drawable/ic_send"/>
</LinearLayout>

Whenever I use R.layout.parent somewhere (for example in setContent from the Activity the view that would get generated would be as follows:

<LinearLayout 
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="vertical">

  <Button .../>
  <!-- PLEASE NOTICE THAT <include/> IS GONE -->
  <!-- AND HAS BEEN REPLACED WITH THE CONTENTS the specified layout -->
  <TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Hello!"/>
  <ImageView android:drawable="@drawable/ic_send"/>
</LinearLayout>

Effectively re-using the layout without writing a full-blown custom view.

Notice: All attributes you specify inside the <include/> tag will effectively override the others specified inside the layout file. Let me illustrate this using an example:

Consider again layout/example.xml. Notice that this time the TextView will shrink to the size of the text both in height and width.

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

And consider the parent: layout/parent.xml. Notice that I am setting the attributes android:layout_width and android:layout_height.

<LinearLayout 
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="vertical">
  <include
    layout="@layout/example"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    />
</LinearLayout>

In this case, when Android replaces <include/> for the contents of @layout/example it will also set android:layout_width="match_parent" and android:layout_height="match_parent" because they were specified on the <include/> tag effectively ignoring the original attributes set inside layout/example.xml (which were set to "wrap_content")