public View(Context context)： 源代码中的解释如下：在Code中实例化一个View就会调用第一个构造函数

　　/**     * Simple constructor to use when creating a view from code.     *     * @param context The Context the view is running in, through which it can     *        access the current theme, resources, etc.     */

public View(Context context, @Nullable AttributeSet attrs): 源代码解释如下：在xml中定义会调用第二个构造函数

/**     * Constructor that is called when inflating a view from XML. This is called     * when a view is being constructed from an XML file, supplying attributes     * that were specified in the XML file. This version uses a default style of     * 0, so the only attribute values applied are those in the Context's Theme     * and the given AttributeSet.     *     * 
     * The method onFinishInflate() will be called after all children have been     * added.     *     * @param context The Context the view is running in, through which it can     *        access the current theme, resources, etc.     * @param attrs The attributes of the XML tag that is inflating the view.     * @see #View(Context, AttributeSet, int)     */

 

public View(Context context, @Nullable AttributeSet attrs, int defStyleAttr): 源代码解释如下:允许继承View的子类使用他们自己的基本样式来生成View

/**     * Perform inflation from XML and apply a class-specific base style from a     * theme attribute. This constructor of View allows subclasses to use their     * own base style when they are inflating. For example, a Button class's     * constructor would call this version of the super class constructor and     * supply R.attr.buttonStyle for defStyleAttr; this     * allows the theme's button style to modify all of the base view attributes     * (in particular its background) as well as the Button class's attributes.     *     * @param context The Context the view is running in, through which it can     *        access the current theme, resources, etc.     * @param attrs The attributes of the XML tag that is inflating the view.     * @param defStyleAttr An attribute in the current theme that contains a     *        reference to a style resource that supplies default values for     *        the view. Can be 0 to not look for defaults.     * @see #View(Context, AttributeSet)     */

 

public View(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes):

源代码解释如下:

　　/**     * Perform inflation from XML and apply a class-specific base style from a     * theme attribute or style resource. This constructor of View allows     * subclasses to use their own base style when they are inflating.     * 
     * When determining the final value of a particular attribute, there are     * four inputs that come into play:     * 
     
           * 
      
Any attribute values in the given AttributeSet.     * 
      
The style resource specified in the AttributeSet (named "style").     * 
      
The default style specified by defStyleAttr.     * 
      
The default style specified by defStyleRes.     * 
      
The base values in this theme.     * 
     
     * 
     * Each of these inputs is considered in-order, with the first listed taking     * precedence over the following ones. In other words, if in the     * AttributeSet you have supplied <Button * textColor="#ff000000">     * , then the button's text will always be black, regardless of     * what is specified in any of the styles.     *     * @param context The Context the view is running in, through which it can     *        access the current theme, resources, etc.     * @param attrs The attributes of the XML tag that is inflating the view.     * @param defStyleAttr An attribute in the current theme that contains a     *        reference to a style resource that supplies default values for     *        the view. Can be 0 to not look for defaults.     * @param defStyleRes A resource identifier of a style resource that     *        supplies default values for the view, used only if     *        defStyleAttr is 0 or can not be found in the theme. Can be 0     *        to not look for defaults.     * @see #View(Context, AttributeSet, int)     */