每一个布局均有一个叫LayoutParams的内部类，如：
LinearLayout.LayoutParams RelativeLayout.LayoutParams AbsoluteLayout.LayoutParams TableLayout.LayoutParams TableLayout.LayoutParams FrameLayout.LayoutParams
此内部类用于指明某个view在其父元素中的位置，以linearLayout为例：
Per-child layout information associated with LinearLayout.
Standard gravity constant that a child supplies to its parent. Defines how the child view should be positioned, on both the X and Y axes, within its enclosing layout.
在LinearLayout中，只有2个xml属性：layout_gravity, layout_weight
但在RelativeLayout中，由于其涉及较多的位置选项，因此有多个xml属性：
Attribute Name Related Method Description android:layout_above Positions the bottom edge of this view above the given anchor view ID. android:layout_alignBaseline Positions the baseline of this view on the baseline of the given anchor view ID. android:layout_alignBottom Makes the bottom edge of this view match the bottom edge of the given anchor view ID. android:layout_alignEnd Makes the end edge of this view match the end edge of the given anchor view ID. android:layout_alignLeft Makes the left edge of this view match the left edge of the given anchor view ID. android:layout_alignParentBottom If true, makes the bottom edge of this view match the bottom edge of the parent. android:layout_alignParentEnd If true, makes the end edge of this view match the end edge of the parent. android:layout_alignParentLeft If true, makes the left edge of this view match the left edge of the parent. android:layout_alignParentRight If true, makes the right edge of this view match the right edge of the parent. android:layout_alignParentStart If true, makes the start edge of this view match the start edge of the parent. android:layout_alignParentTop If true, makes the top edge of this view match the top edge of the parent. android:layout_alignRight Makes the right edge of this view match the right edge of the given anchor view ID. android:layout_alignStart Makes the start edge of this view match the start edge of the given anchor view ID. android:layout_alignTop Makes the top edge of this view match the top edge of the given anchor view ID. android:layout_alignWithParentIfMissing If set to true, the parent will be used as the anchor when the anchor cannot be be found for layout_toLeftOf, layout_toRightOf, etc. android:layout_below Positions the top edge of this view below the given anchor view ID. android:layout_centerHorizontal If true, centers this child horizontally within its parent. android:layout_centerInParent If true, centers this child horizontally and vertically within its parent. android:layout_centerVertical If true, centers this child vertically within its parent. android:layout_toEndOf Positions the start edge of this view to the end of the given anchor view ID. android:layout_toLeftOf Positions the right edge of this view to the left of the given anchor view ID. android:layout_toRightOf Positions the left edge of this view to the right of the given anchor view ID. android:layout_toStartOf Positions the end edge of this view to the start of the given anchor view ID.
总而言之，LayoutParams子类用于指定某个元素的位置信息。
转载于:https://www.cnblogs.com/jinhong-lu/p/4559509.html
