Padding and Margins

Using Padding and Margins with Views and Layouts : 

Padding adds spacing to a View (or a widget subclassed therefrom), so that that View’s content is

offset by a certain number of pixels on each of the four sides. This way, the content doesn’t touch

the edges of the View and look unprofessional. In other words, padding adds space around the

outside of a View’s content, and you can choose to do so on any of the four sides of the View object.

When using padding, the padding is considered to be part of the View, which may affect the way

Android lays out the View. Remember, we are talking here about a View Class or Object, that is, a

user interface widget, not the view on your Android device’s screen!

Padding values are only available to Views, not to ViewGroups (and thus not available in screen layout

containers). 

This is logical because View objects (usually widgets) are contained inside something

(ViewGroups) but contain nothing inside of them, that is, they are what they are (Button, Clock, Radio

Button, Text Field, etc.).

ViewGroups instead support margins, which allow the same results as padding to be obtained,

except that the margins are not considered part of the ViewGroup. For me, this makes UI design more

organized and easy to remember: Views use padding values and ViewGroups use margin values and

also can use padding values.

Setting Padding in Views:

Padding can be set for your View objects (usually widgets) in three ways.

The first and easiest way to set a padding value for a UI element widget is to use the Properties Editor pane in Eclipse, where all of the properties of a selected UI element in the Graphical Layout Editor will be displayed on the right side (or wherever you place that pane) of the Eclipse IDE.

The second way to set properties of a UI widget is in the XML editor pane, where when you type

android: a window containing all of the parameter options (including padding settings) will pop-up

as soon as you type the colon symbol after you type in android (in lower case). Then you can

double-click on the parameter that you want and type in its value or even type in the entire

parameter from memory without using the helper that works in the XML editing pane.

Most of the time you will use one of these two methods to set padding; using Java for setting padding values is not a “Best Practice,” unless you are doing something really vanguard and need to have real-time

control over padding values.

That said, padding can also be set via your Java code, using the .setPadding() method with four

values, for left, top, right, and bottom. Think of going around a clock, starting at 9:00, separated by

commas. So, to put a four-pixel border inside your view, you would use the following (remember that

the order of parameters is left, top, right, bottom):

objectName.setPadding(4,4,4,4);

You can also separate each side in the Java methods, just like you can with the XML tag parameters.

So, to get the padding for the left side of the view, use .getPaddingLeft(). To set just the padding on

the top to eight pixels, you would write something like this:

ObjectName.setPaddingTop(8);

Setting Margins in ViewGroups : 

For ViewGroups, including layout containers (the subject of this chapter), the easiest way to set

margins during development is via the XML parameters for any ViewGroup object.

Four layout margin values are available in XML:

1. android:layout marginBottom
2. android:layout marginLeft
3. android:layout marginRight
4. android:layout marginTop

We used the android:layout_marginTop in our RelativeLayout example earlier to

space the text entry UI element down and away from the text label UI element.