• LayoutInflater layoutInflater = LayoutInflater.from(context);
  
• LayoutInflater layoutInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE)

public static LayoutInflater from(Context context) {
    return (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
    synchronized (mConstructorArgs) {
        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
        final Context inflaterContext = mContext;
        final AttributeSet attrs = Xml.asAttributeSet(parser);
        Context lastContext = (Context) mConstructorArgs[0];
        mConstructorArgs[0] = inflaterContext;
        View result = root;//最终返回值
        try {
            // Look for the root node.查找根节点
            int type;
            while ((type = parser.next()) != XmlPullParser.START_TAG &&
                    type != XmlPullParser.END_DOCUMENT) {
                // Empty
            }
            if (type != XmlPullParser.START_TAG) {//没有找到根节点
                throw new InflateException(parser.getPositionDescription()+": No start tag found!");
            }
            final String name = parser.getName();
            if (TAG_MERGE.equals(name)) {
                if (root == null || !attachToRoot) {
                    throw new InflateException("<merge /> can be used only with a valid "
                            + "ViewGroup root and attachToRoot=true");
                }
                rInflate(parser, root, inflaterContext, attrs, false);
            } else {
                // Temp is the root view that was found in the xml 创建根节点的View
                final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                ViewGroup.LayoutParams params = null;
                if (root != null) {
                    // Create layout params that match root, if supplied 如果提供了LayoutParams
                    params = root.generateLayoutParams(attrs);
                    if (!attachToRoot) {//即inflate(resId , parent,false)时的逻辑
                        // Set the layout params for temp if we are not attaching. (If we are, we use addView, below)
                        temp.setLayoutParams(params); // 为xml中的root设置LayoutParams
                    }
                }
                // Inflate all children under temp against its context.
                rInflateChildren(parser, temp, attrs, true);
                // We are supposed to attach all the views we found (int temp) to root. Do that now.
                if (root != null && attachToRoot) {//即inflate(resId , parent,true)时的逻辑
                    root.addView(temp, params);  //将temp按照params添加到root中
                }
                // Decide whether to return the root that was passed in or the top view found in xml.
                if (root == null || !attachToRoot) { //即inflate(resId , null)时的逻辑
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {
            InflateException ex = new InflateException(e.getMessage());
            ex.initCause(e);
            throw ex;
        } catch (Exception e) {
            InflateException ex = new InflateException(parser.getPositionDescription()+ ": " + e.getMessage());
            ex.initCause(e);
            throw ex;
        } finally {
            // Don‘t retain static reference on context.
            mConstructorArgs[0] = lastContext;
            mConstructorArgs[1] = null;
        }
        Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        return result;
    }
}