Question

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.RelativeLayout;

public class register_activity extends Activity {


@Override
public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register);

        RelativeLayout RLayout = (RelativeLayout) View.inflate(this, R.layout.register, null);

        RelativeLayout.LayoutParams p = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.FILL_PARENT,
                RelativeLayout.LayoutParams.WRAP_CONTENT
        );

        Button btnCreateNew = new Button(this);
        btnCreateNew.setText("Create New User");
        btnCreateNew.offsetTopAndBottom(10);
        btnCreateNew.offsetLeftAndRight(10);
        RLayout.addView(btnCreateNew, p);

    }
}

So that code works and runs just fine, only I can not see the button being displayed. The layout is simply blank with nothing inside it.

What is wrong?

Answer 1

You got a NullPointerException, right? (Check your LogCat!)

The reason:

1. You create a Button as a member variable with this as a parameter. That might cause some trouble as this might not be defined when new Button(this) is called. Move the initialization into onCreate

2. Your RLayout will be null, and here I am very sure. The reason is, that you can’t call findViewById() before you called setContentView(). If you call it before, Android has no idea where to look at and returns null.

update

As you changed your question quite a bit, here is my updated answer:

You set your content to R.layout.register and after that you inflate it again.

My solution for you: just use setContentView(R.layout.register), than use findViewById(R.id.layout_id) and finally create and add your button:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.register);

    RelativeLayout RLayout = (RelativeLayout) findViewById(R.id.layout_id);

    RelativeLayout.LayoutParams p = new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.FILL_PARENT,
            RelativeLayout.LayoutParams.WRAP_CONTENT
    );

    Button btnCreateNew = new Button(this);
    btnCreateNew.setText("Create New User");
    btnCreateNew.offsetTopAndBottom(10);
    btnCreateNew.offsetLeftAndRight(10);
    RLayout.addView(btnCreateNew, p);
}

Of course you can also add the button in the xml layout directly. I would prefer this way, because you have a better separation between layout and code.

Basic XML structure (style it to as you want):

<RelativeLayout android:id="@+id/layout_id"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
    <Button android:id="@+id/button_id"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:text="@string/button_text"/>
</RelativeLayout>

The reason for you blank screen was, that you added the button to the new created RLayout but this layout was never part of your screen (never added by setContentView())