View的几种计算模式

1.父view未对子view的大小做限制，子view需要多大，就给多大

随便

/**
  * Measure specification mode: The parent has not imposed any constraint
  * on the child. It can be whatever size it wants.
*/
public static final int UNSPECIFIED = 0 << MODE_SHIFT;

2.父view指定了子view的大小

等于

/**
  * Measure specification mode: The parent has determined an exact size
  * for the child. The child is going to be given those bounds regardless
  * of how big it wants to be.
*/
public static final int EXACTLY     = 1 << MODE_SHIFT;

3.父view指定了子view的最大大小

小于等于

/**
  * Measure specification mode: The child can be as large as it wants up
   * to the specified size.
*/
public static final int AT_MOST     = 2 << MODE_SHIFT;