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State List Drawable


A StateListDrawable is a drawable object defined in XML that uses a several different images to represent the same graphic, depending on the state of the object. For example, a Button widget can exist in one of several different states (pressed, focused, or niether) and, using a state list drawable, you can provide a different background image for each state.

You can describe the state list in an XML file. Each graphic is represented by an <item> element inside a single <selector> element. Each <item> uses various attributes to describe the state in which it should be used as the graphic for the drawable.

During each state change, the state list is traversed top to bottom and the first item that matches the current state is used—the selection is not based on the “best match,” but simply the first item that meets the minimum criteria of the state.

file location:
res/drawable/filename.xml
The filename is used as the resource ID.

attributes:
android:drawable
Drawable resource. Required. Reference to a drawable resource.
android:state_pressed
Boolean. “true” if this item should be used when the object is pressed (such as when a button is touched/clicked); “false” if this item should be used in the default, non-pressed state.
android:state_focused
Boolean. “true” if this item should be used when the object has input focus (such as when the user selects a text input); “false” if this item should be used in the default, non-focused state.
android:state_hovered
Boolean. “true” if this item should be used when the object is being hovered by a cursor; “false” if this item should be used in the default, non-hovered state. Often, this drawable may be the same drawable used for the “focused” state.
Introduced in API level 14.
android:state_selected
Boolean. “true” if this item should be used when the object is the current user selection when navigating with a directional control (such as when navigating through a list with a d-pad); “false” if this item should be used when the object is not selected.
The selected state is used when focus (android:state_focused) is not sufficient (such as when list view has focus and an item within it is selected with a d-pad).
android:state_checkable
Boolean. “true” if this item should be used when the object is checkable; “false” if this item should be used when the object is not checkable. (Only useful if the object can transition between a checkable and non-checkable widget.)
android:state_checked
Boolean. “true” if this item should be used when the object is checked; “false” if it should be used when the object is un-checked.
android:state_enabled
Boolean. “true” if this item should be used when the object is enabled (capable of receiving touch/click events); “false” if it should be used when the object is disabled.
android:state_activated
Boolean. “true” if this item should be used when the object is activated as the persistent selection (such as to “highlight” the previously selected list item in a persistent navigation view); “false” if it should be used when the object is not activated.
Introduced in API level 11.
android:state_window_focused
Boolean. “true” if this item should be used when the application window has focus (the application is in the foreground), “false” if this item should be used when the application window does not have focus (for example, if the notification shade is pulled down or a dialog appears).
Note: Remember that Android applies the first item in the state list that matches the current state of the object. So, if the first item in the list contains none of the state attributes above, then it is applied every time, which is why your default value should always be last (as demonstrated in the following example).
EXAMPLE:
XML file saved at res/drawable/button.xml:
<?xml version=”1.0″ encoding=”utf-8″?>
    <item android:state_pressed=”true”
          android:drawable=”@drawable/button_pressed” /> <!– pressed –>
    <item android:state_focused=”true”
          android:drawable=”@drawable/button_focused” /> <!– focused –>
    <item android:state_hovered=”true”
          android:drawable=”@drawable/button_focused” /> <!– hovered –>
    <item android:drawable=”@drawable/button_normal” /> <!– default –>
</selector>
This layout XML applies the state list drawable to a Button:
<Button
    android:layout_height=”wrap_content”
    android:layout_width=”wrap_content”
    android:background=”@drawable/button” />
Source : developer.android.com
Categories: Android
  1. 13/09/2014 at 3:20 PM

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