Is it possible to add a button to an empty MainActivity in android?

I have an empty Activity_main layout. I want to add a number of buttons that have to be a certain % of the screen width and for this reason I want to add them programmatically. Every example on this site uses a LinearLayout. Is it possible to add a button directly to the Activity_main?

Thanks.

You need a ViewGroup because it is the base class for layouts and views containers.

If don't want to use a linear layout, you can use a constraint layout. Constraint layouts come with Guidelines - they can help you measure a specific percentage of the screen and align buttons (or views) next to them.

The image above is an example of how guidelines work. The first is a vertical guideline that takes up 25% of the screen (you can think of it as splitting the screen vertically into 4 pieces). The second is a horizontal guideline that takes up 50% of the screen (splitting the screen horizontally into 2 pieces).

i want to add a number of buttons that have to be a certain % of the screen width

You can achieve this with guidelines. Here's how to do it using only xml:

<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="com.chornge.myapplication.MainActivity">

    <android.support.constraint.Guideline
        android:id="@+id/vertical_guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_percent="0.25" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toRightOf="@id/vertical_guideline" />

    <android.support.constraint.Guideline
        android:id="@+id/horizontal_guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="0.50" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@id/horizontal_guideline" />

</android.support.constraint.ConstraintLayout>

And here's how to create the same effect using only Java:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // setContentView(R.layout.activity_main);

    ConstraintLayout constraintLayout = new ConstraintLayout(this);
    constraintLayout.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
            ViewGroup.LayoutParams.MATCH_PARENT));
    setContentView(constraintLayout);

    /* vertical guideline */

    Guideline verticalGuide = new Guideline(this);
    ConstraintLayout.LayoutParams verticalGuideParams =
            new ConstraintLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT);

    verticalGuideParams.guidePercent = 0.25f;
    verticalGuideParams.orientation = LinearLayout.VERTICAL;
    verticalGuide.setLayoutParams(verticalGuideParams);
    verticalGuide.setId(View.generateViewId());
    constraintLayout.addView(verticalGuide);

    /* create button1 and align its left edge to the right edge of vertical guideline*/

    Button button1 = new Button(this);
    button1.setId(View.generateViewId());
    ConstraintLayout.LayoutParams button1Params =
            new ConstraintLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT);

    button1Params.leftToRight = verticalGuide.getId();
    button1.setLayoutParams(button1Params);
    constraintLayout.addView(button1);

    /* horizontal guideline */

    Guideline horizontalGuide = new Guideline(this);
    ConstraintLayout.LayoutParams horizontalGuideParams =
            new ConstraintLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT);

    horizontalGuideParams.guidePercent = 0.5f;
    horizontalGuideParams.orientation = LinearLayout.HORIZONTAL;
    horizontalGuide.setLayoutParams(horizontalGuideParams);
    horizontalGuide.setId(View.generateViewId());
    constraintLayout.addView(horizontalGuide);

    /* create button2 and align its top edge to the bottom edge of horizontal guideline*/

    Button button2 = new Button(this);
    button2.setId(View.generateViewId());
    ConstraintLayout.LayoutParams button2Params =
            new ConstraintLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT);

    button2Params.topToBottom = horizontalGuide.getId();
    button2.setLayoutParams(button2Params);
    constraintLayout.addView(button2);
}

Note:

• You still need a ViewGroup to be your base class (either LinearLayout or RelativeLayout or ConstraintLayout)
• You can make any View (Button, TextView, EditText, etc) align with another View or ViewGroup using topToTop or topToBottom or bottomToTop or bottomToBottom or leftToLeft or leftToRight or rightToLeft or rightToRight.
• You can use any percentage you want for your guidelines: 5%, 33.3%, 80% which translates to 0.05f, 0.333f, 0.8f, respectively.