make a single button width to fill parent programmatically

Question

How do I make a single button width to fill parent programmatically? I have done this but it cannot seem to work it is still located on top left with width just wrapping the content... here is some of the code on the button creation...

public class TEST_GIFDisplay extends Activity implements View.OnClickListener {

    SurfaceView sview;
    GifRun gr = new GifRun();
    Button btnBack;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        sview = new SurfaceView(this);
        sview.setZOrderOnTop(true);

        gr.LoadGiff(sview, this, R.drawable.smiley);

        LinearLayout linearLayout1 = new LinearLayout(this);
        linearLayout1.setOrientation(LinearLayout.VERTICAL);
        linearLayout1.setBackgroundColor(Color.parseColor("#27ae60"));
        linearLayout1.setLayoutParams(new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT));

        LinearLayout linearLayout2 = new LinearLayout(this);
        linearLayout2.setOrientation(LinearLayout.VERTICAL);
        linearLayout2.setBackgroundColor(Color.parseColor("#27ae60"));
        linearLayout2.setLayoutParams(new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT));

        LinearLayout.LayoutParams p = new   
        LinearLayout.LayoutParams(LinearLayout.LayoutParams.FILL_PARENT,   
        LinearLayout.LayoutParams.WRAP_CONTENT);
        p.weight = 1.0f;

        btnBack = new Button (this);
        btnBack.setText("Back");
        btnBack.setBackgroundColor(Color.parseColor("#f1c40f"));
        btnBack.setGravity(Gravity.CENTER_HORIZONTAL);
        btnBack.setLayoutParams(p);
        btnBack.setOnClickListener(this);

        linearLayout2.addView(btnBack);
        linearLayout1.addView(linearLayout2);
        linearLayout1.addView(sview);

        setContentView(linearLayout1);
    }

    @Override
    public void onClick(View view) {
        btnBack = (Button) view;
        btnBack.setBackgroundColor(Color.parseColor("#2980b9")); //color change
        new CountDownTimer(100, 50) {

            @Override
            public void onTick(long arg0) {
                // TODO Auto-generated method stub
            }

            @Override
            public void onFinish() {
                btnBack.setBackgroundColor(Color.parseColor("#f1c40f")); // original color
            }
        }.start();//end color changed

        finish();
    }
}

Answer 1

You are adding the Button to linearLayout2. You should change the linearLayout2's width to MATCH_PARENT

linearLayout2.setLayoutParams(new ViewGroup.LayoutParams(
        ViewGroup.LayoutParams.MATCH_PARENT,
        ViewGroup.LayoutParams.WRAP_CONTENT));

I hope this helps.

P.S: You can create Button's selectors for pressed and selected states, instead of using timer to show a pressed button effect. Here is a basic link that can help you in achieving this : android button selector