android layout / android textsize

Constant	Value	Description
fill_parent	-1	The view should be as big as its parent (minus padding). This constant is deprecated starting from API Level 8 and is replaced by  match_parent .
match_parent	-1	The view should be as big as its parent (minus padding). Introduced in API Level 8.
wrap_content	-2	The view should be only big enough to enclose its content (plus padding).

实质上layout 只存在了两种，一种是match_parent, 另一种是 wrap_content. fill_parent 已经被match_parent所取代

-----------------------textsize-------------------------------

http://developer.android.com/training/multiscreen/screendensities.html

 Therefore, when specifying dimensions, always use either 

dp

 or 

sp

 units. A 

dp

 is a density-independent pixel that corresponds to the physical size of a pixel at 160 dpi. An 

sp

 is the same base unit, but is scaled by the user's preferred text size (it’s a scale-independent pixel), so you should use this measurement unit when defining text size (but never for layout sizes).

For example, when you specify spacing between two views, use

dp

 rather than 

px

:

<Button android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="@string/clickme"
    android:layout_marginTop="20dp" />      

When specifying text size, always use 

sp

:

<TextView android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:textSize="20sp" />      

dp可以在不同的分辨率下实现物理尺寸“差不多”的效果

sp主要处理文字的大小