Tag Archives: layout

How to center a Button in an Android Layout?

Android,

In my last Android Training several people asked how they could center a single view, e.g. a Button, so I assume it is worth a short blog entry.

If you have a single Button in your Activity and you want to center it the simplest way is to use a RelativeLayout and set the android:layout_centerInParent=”true” property on the Button.

For example like this:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <Button
        android:id="@+id/captureFront"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:onClick="onClick"
        android:text="Make Photo" />

</RelativeLayout>

Alternative you can do this via a LinearLayout (thanks to Ravi Tamada via Twitter for the tip.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" 
    android:gravity="center"
    >

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello" 
        />

</LinearLayout>

Android – Hacking layouts

Android, ,

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.

Android – Making efficient layouts

Android, , ,

Android Programming is a lot about efficiency to have snappy user interfaces. The Android SDK provides two nice tools to help building efficient UI’s. In the tools directory you find the tools:

layoutopt and
hierarchyviewer.

layoutopt is a command line tool which can analyse a layout resource file and tell you what is not required and hierarchyviewer is a tool to view the View hierarchy of your running application.

I suggest to have a look at these tools and check your layouts especially if you have created a complex application.