.LayoutParams 介绍

.LayoutParams  其实就是一个Layout信息容器，装了 Layout的宽，高的信息，告诉他们的父容器，他们想放在哪，多大

下面是2种用法：

setLayoutParams(new TableRow.LayoutParams(TableRow.LayoutParams.FILL_PARENT,TableRow.LayoutParams.FILL_PARENT));

FrameLayout.LayoutParams lytp = new FrameLayout.LayoutParams(80,LayoutParams.WRAP_CONTENT);
lytp .gravity = Gravity.CENTER;
btn.setLayoutParams(lytp);

 可以这样去形容LayoutParams，在象棋的棋盘上，每个棋子都占据一个位置，也就是每个棋子都有一个位置的信息，如这个棋子在4行4列，这里的“4行4列”就是棋子的LayoutParams。


       但LayoutParams类也只是简单的描述了宽高，宽和高都可以设置成三种值：
       1，一个确定的值；
       2，FILL_PARENT，即填满（和父容器一样大小）；
       3，WRAP_CONTENT，即包裹住组件就好。

下面是谷歌原文：

Class Overview

---

LayoutParams are used by views to tell their parents how they want to be laid out. See ViewGroup Layout Attributes for a list of all child view attributes that this class supports.

The base LayoutParams class just describes how big the view wants to be for both width and height. For each dimension, it can specify one of:

• FILL_PARENT (renamed MATCH_PARENT in API Level 8 and higher), which means that the view wants to be as big as its parent (minus padding)
• WRAP_CONTENT, which means that the view wants to be just big enough to enclose its content (plus padding)
• an exact number

There are subclasses of LayoutParams for different subclasses of ViewGroup. For example, AbsoluteLayout has its own subclass of LayoutParams which adds an X and Y value.

Developer Guides

For more information about creating user interface layouts, read the XML Layouts developer guide.

Summary

---

XML Attributes
Attribute Name	Related Method	Description
android:layout_height		Specifies the basic height of the view.
android:layout_width		Specifies the basic width of the view.

Constants
int	FILL_PARENT	Special value for the height or width requested by a View.
int	MATCH_PARENT	Special value for the height or width requested by a View.
int	WRAP_CONTENT	Special value for the height or width requested by a View.

Fields
public int	height	Information about how tall the view wants to be.
public  LayoutAnimationController.AnimationParameters	layoutAnimationParameters	Used to animate layouts.
public int	width	Information about how wide the view wants to be.

Public Constructors
	ViewGroup.LayoutParams( Context c,  AttributeSet attrs) Creates a new set of layout parameters.
	ViewGroup.LayoutParams(int width, int height) Creates a new set of layout parameters with the specified width and height.
	ViewGroup.LayoutParams( ViewGroup.LayoutParams source) Copy constructor.

Protected Methods
void	setBaseAttributes( TypedArray a, int widthAttr, int heightAttr) Extracts the layout parameters from the supplied attributes.

[Expand] Inherited Methods
From class java.lang.Object

XML Attributes

---

android:layout_height

Specifies the basic height of the view. This is a required attribute for any view inside of a containing layout manager. Its value may be a dimension (such as "12dip") for a constant height or one of the special constants.

May be a dimension value, which is a floating point number appended with a unit such as "14.5sp". Available units are: px (pixels), dp (density-independent pixels), sp (scaled pixels based on preferred font size), in (inches), mm (millimeters).

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

May be one of the following constant values.

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).

This corresponds to the global attribute resource symbol layout_height.

Related Methods

android:layout_width

Specifies the basic width of the view. This is a required attribute for any view inside of a containing layout manager. Its value may be a dimension (such as "12dip") for a constant width or one of the special constants.

May be a dimension value, which is a floating point number appended with a unit such as "14.5sp". Available units are: px (pixels), dp (density-independent pixels), sp (scaled pixels based on preferred font size), in (inches), mm (millimeters).

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

May be one of the following constant values.

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).

This corresponds to the global attribute resource symbol layout_width.

Related Methods

Constants

---

public static final int FILL_PARENT

Since:  API Level 1

Special value for the height or width requested by a View. FILL_PARENT means that the view wants to be as big as its parent, minus the parent's padding, if any. This value is deprecated starting in API Level 8 and replaced by MATCH_PARENT.

Constant Value: -1 (0xffffffff)

public static final int MATCH_PARENT

Since:  API Level 8

Special value for the height or width requested by a View. MATCH_PARENT means that the view wants to be as big as its parent, minus the parent's padding, if any. Introduced in API Level 8.

Constant Value: -1 (0xffffffff)

public static final int WRAP_CONTENT

Since:  API Level 1

Special value for the height or width requested by a View. WRAP_CONTENT means that the view wants to be just large enough to fit its own internal content, taking its own padding into account.

Constant Value: -2 (0xfffffffe)

Fields

---

public int height

Since:  API Level 1

Information about how tall the view wants to be. Can be one of the constants FILL_PARENT (replaced by MATCH_PARENT , in API Level 8) or WRAP_CONTENT. or an exact size.

public LayoutAnimationController.AnimationParameters layoutAnimationParameters

Since:  API Level 1

Used to animate layouts.

public int width

Since:  API Level 1

Information about how wide the view wants to be. Can be one of the constants FILL_PARENT (replaced by MATCH_PARENT , in API Level 8) or WRAP_CONTENT. or an exact size.

Public Constructors

---

public ViewGroup.LayoutParams (Context c, AttributeSet attrs)

Since:  API Level 1

Creates a new set of layout parameters. The values are extracted from the supplied attributes set and context. The XML attributes mapped to this set of layout parameters are:

• layout_width: the width, either an exact value, WRAP_CONTENT, or FILL_PARENT (replaced by MATCH_PARENT in API Level 8)
• layout_height: the height, either an exact value, WRAP_CONTENT, or FILL_PARENT (replaced by MATCH_PARENT in API Level 8)

Parameters

c	the application environment
attrs	the set of attributes from which to extract the layout parameters' values

public ViewGroup.LayoutParams (int width, int height)

Since:  API Level 1

Creates a new set of layout parameters with the specified width and height.

Parameters

width	the width, either WRAP_CONTENT, FILL_PARENT (replaced by MATCH_PARENT in API Level 8), or a fixed size in pixels
height	the height, either WRAP_CONTENT, FILL_PARENT (replaced by MATCH_PARENT in API Level 8), or a fixed size in pixels

public ViewGroup.LayoutParams (ViewGroup.LayoutParams source)

Since:  API Level 1

Copy constructor. Clones the width and height values of the source.

Parameters

source	The layout params to copy from.

Protected Methods

---

protected void setBaseAttributes (TypedArray a, int widthAttr, int heightAttr)

Since:  API Level 1

Extracts the layout parameters from the supplied attributes.

Parameters

a	the style attributes to extract the parameters from
widthAttr	the identifier of the width attribute
heightAttr	the identifier of the height attribute