填充View最终都是调用LayoutInflater的public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)三个参数方法

    /**
     * Inflate a new view hierarchy from the specified xml resource. Throws
     * {@link InflateException} if there is an error.
     *
     * @param resource ID for an XML layout resource to load (e.g.,
     *        <code>R.layout.main_page</code>)
     * @param root Optional view to be the parent of the generated hierarchy (if
     *        <em>attachToRoot</em> is true), or else simply an object that
     *        provides a set of LayoutParams values for root of the returned
     *        hierarchy (if <em>attachToRoot</em> is false.)
     * @param attachToRoot Whether the inflated hierarchy should be attached to
     *        the root parameter? If false, root is only used to create the
     *        correct subclass of LayoutParams for the root view in the XML.
     * @return The root View of the inflated hierarchy. If root was supplied and
     *         attachToRoot is true, this is root; otherwise it is the root of
     *         the inflated XML file.
     */
    public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot){
           ··· ···
        return view；
    }

文档解释说明：

     /**
     * 只能填充特定格式的xml也就是得符合布局格式的xml，否则抛出异常InflateException。
     * @param resource 要填充的资源id
     * @param root 这个要和第三个参数有关系。
     *             若是attachToRoot为true，那么root的意义是，从resource填充成的view对象的父控件；
     *             若是attachToRoot为false，那么root的意义是，可以为resource生成的view对象的根布局提供一系LayoutParams参数的控件。
     *             若root为null，也就是我们不指定父控件，那么新生产的view对象的根布局的某些参数会失效，比如Layout_width和Layout_height会失效。
     * @param attachToRoot 是否附着在root上
     * @return 如果attachToRoo为false，那么返回resource填充的View；
     *         如果attachToRoo为true，那么返回root。
     */
    public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot){
           ··· ···
        return view；
    }

常用填充View的方式有三种：

1. View的静态方法，直接获取LayoutInflater进行填充

     /**
     * Inflate a view from an XML resource.  This convenience method wraps the {@link
     * LayoutInflater} class, which provides a full range of options for view inflation.
     *
     * @param context The Context object for your activity or application.
     * @param resource The resource ID to inflate
     * @param root A view group that will be the parent.  Used to properly inflate the
     * layout_* parameters.
     * @see LayoutInflater
     */
    public static View inflate(Context context, @LayoutRes int resource, ViewGroup root) {
        LayoutInflater factory = LayoutInflater.from(context);
        return factory.inflate(resource, root);
    }

2. LayoutInflater的静态方法获取LayoutInflater，然后调用Inflater填充

     /**
     * Obtains the LayoutInflater from the given context.
     */
    public static LayoutInflater from(Context context) {
        LayoutInflater LayoutInflater =
                (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        if (LayoutInflater == null) {
            throw new AssertionError("LayoutInflater not found.");
        }
        return LayoutInflater;
    }

3. 通过系统SystemService获取填充器，然后调用Inflater填充

LayoutInflater LayoutInflater = 
 (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE)

注意：

View的填充方式只有两个参数，也就是调用的inflate(resource, root, root != null)
而RecyclerViewonCreateViewHolder创建View填充时一定是inflate(resource, null)orinflate(resource, root, false)
root为空时view的根节点部分参数无效
否则会报

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