Android – Hacking layouts

One common mis-understanding seem to be that Android starters seem to think that a layout can only be defined via a XML resource. While this is the most common way of defining a layout in most cases you can also define a complete layout via programming code.

For example create a project “de.vogella.android.codelayout” with the activity “CodeLayout” and the following coding.

package de.vogella.android.codelayout;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

public class CodeLayout extends Activity {
	/** Called when the activity is first created. */
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		LayoutParams params1 = new LayoutParams(LayoutParams.MATCH_PARENT,
				LayoutParams.WRAP_CONTENT);

		TextView text = new TextView(this);
		text.setText("Hello");
		text.setLayoutParams(params1);
		EditText edit = new EditText(this);
		edit.setHint("This is your input...");
		edit.setLayoutParams(params1);
		Button button = new Button(this);
		button.setText("Press me");
		button.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				Toast makeText = Toast.makeText(v.getContext(), "Pressed", 200);
				makeText.show();
			}
		});
		LinearLayout layout = new LinearLayout(this);
		layout.setOrientation(LinearLayout.VERTICAL);
		layout.setPadding(10, 10, 10, 10);
		layout.addView(text);
		layout.addView(edit);
		layout.addView(button);
		setContentView(layout);
	}
}

As you can see the layout is completely created via programming code.

Why is it better to define the layout of an application via XML? See Android Layout Overview.

But even if you define your layout via XML then this layout will be inflated in Java objects by the class “LayoutInflator” which will parse the XML, creates elements for the ViewGroups and Views and calls the setter for the attributes defined in the XML.

Hope this helps.