CODEWITHSUNDEEP
androidviewmargin
cajsaiko
cajsaiko

Reputation: 1047

Android view support margin?

From the developer guide it says that

though a view can define a padding, it does not provide any support for margins. However, view groups provide such a support.

but why i can set layout_margin attributes in ImageView,EditView and so on,they exist and work just like padding,

I can't understand what the guide says, Can someone help me to understand it?

Upvotes: 1

Views: 377

Answers (2)

Paul Davies
Paul Davies

Reputation: 107

View class does not contain margins. It contains the padding because padding offset the contents of the view. Margin is meant to offset the view itself from the parent, ViewGroup. As such, the margins are contained in the ViewGroup class. However remember the principle of inheritance. A view is a child of the ViewGroup class. As a result, it inherits the properties of the ViewGroup, including the margins. So when you apply the margin on the view, it responds because it already has the margins properties by virtue of inheritance.

Upvotes: 0

Zielony
Zielony

Reputation: 16537

Basically that means that margins are defined in xml for child views, but are used by their parent.

Technically, paddings are fields of the View class. Paddings are being used in the View.draw() method by a View itself. See:

http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.0.2_r1/android/view/View.java#15156

Margins are fields of the MarginLayoutParams class. Margins are used by a ViewGroup to layout its children. See:

http://developer.android.com/reference/android/view/ViewGroup.MarginLayoutParams.html

EDIT:

Margins are loaded to MarginLayoutParams and then used in the layouting phase.

Method which uses these xml attributes to create MarginLayoutParams in FrameLayout: http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.0.2_r1/android/widget/FrameLayout.java#678

Loading margins: http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.0.2_r1/android/view/ViewGroup.java#6619

Layouting: http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.0.2_r1/android/widget/LinearLayout.java#1539

Upvotes: 1

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