获取方式

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

或者

LayoutInflater layoutInflater = LayoutInflater.from(context);

LayoutInflater方法

参数说明
resource:布局文件id。
root:根视图不为空时，如果attachToRoot为true，则将inflate视图添加到根视图上，为false，则将根视图的布局参数（LayoutParams）设置给inflate视图。
attachToRoot:是否添加到根视图上。

public View inflate(XmlPullParser parser, ViewGroup root) {
    return inflate(parser, root, root != null);
}

public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
    final Resources res = getContext().getResources();
    final XmlResourceParser parser = res.getLayout(resource);
    try {
        return inflate(parser, root, attachToRoot);
    } finally {
        parser.close();
    }
}

public View inflate(XmlPullParser parser, ViewGroup root) {
    return inflate(parser, root, root != null);
}

public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
    // mConstructorArgs为长度2的Object数组，mConstructorArgs[0]当前Context对象，mConstructorArgs[1]为当前布局的AttributeSet。
    synchronized (mConstructorArgs) {
        // Trace事件
        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;
        try {
            // Pull解析文章，http://www.jianshu.com/p/189b91ef5d61
            int type;
            // 跳过START_DOCUMENT类型，直接处理START_TAG
            while ((type = parser.next()) != XmlPullParser.START_TAG &&
                type != XmlPullParser.END_DOCUMENT) {
                // Empty
            }
            if (type != XmlPullParser.START_TAG) {
                throw new InflateException(parser.getPositionDescription()
                     + ": No start tag found!");
            }
            final String name = parser.getName();
            // 判断merge标签，如果存在根视图不能为空，attachToRoot不能为false
            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");
                }
                // 参考下面rInflate源码，此时parser为merge标签内容
                rInflate(parser, root, inflaterContext, attrs, false);
            } else {
                // Temp is the root view that was found in the xml
                // 创建inflate视图
                final View temp = createViewFromTag(root, name, inflaterContext, attrs);
                ViewGroup.LayoutParams params = null;
                // 获取根视图布局参数
                if (root != null) {
                    // Create layout params that match root, if supplied
                    params = root.generateLayoutParams(attrs);
                    // 如果attachToRoot为false，把根视图布局参数赋给inflate视图
                    if (!attachToRoot) {
                        // Set the layout params for temp if we are not
                        // attaching. (If we are, we use addView, below)
                        temp.setLayoutParams(params);
                    }
                }
                // 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.
                // 如果attachToRoot为true并且根视图不为空，添加inflate视图到根视图上，root和result是同一对象
                if (root != null && attachToRoot) {
                    root.addView(temp, params);
                }
                // Decide whether to return the root that was passed in or the
                // top view found in xml.
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }
        } catch (XmlPullParserException e) {
            final InflateException ie = new InflateException(e.getMessage(), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        } catch (Exception e) {
            final InflateException ie = new InflateException(parser.getPositionDescription()
                    + ": " + e.getMessage(), e);
            ie.setStackTrace(EMPTY_STACK_TRACE);
            throw ie;
        } finally {
            // Don't retain static reference on context.
            mConstructorArgs[0] = lastContext;
            mConstructorArgs[1] = null;
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
        return result;
    }
}

rInflate方法

void rInflate(XmlPullParser parser, View parent, Context context,
            AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
    final int depth = parser.getDepth();
    int type;
    while (((type = parser.next()) != XmlPullParser.END_TAG ||
            parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
        if (type != XmlPullParser.START_TAG) {
            continue;
        }
        final String name = parser.getName();
        if (TAG_REQUEST_FOCUS.equals(name)) {
            // 处理requestFocus标签
            parseRequestFocus(parser, parent);
        } else if (TAG_TAG.equals(name)) {
            // 处理tag标签
            parseViewTag(parser, parent, attrs);
        } else if (TAG_INCLUDE.equals(name)) {
            // 处理include标签
            if (parser.getDepth() == 0) {
                throw new InflateException("<include /> cannot be the root element");
            }
            parseInclude(parser, context, parent, attrs);
        } else if (TAG_MERGE.equals(name)) {
            // merge标签不能嵌套merge标签
            throw new InflateException("<merge /> must be the root element");
        } else {
            // 处理merge标签
            // 创建视图
            final View view = createViewFromTag(parent, name, context, attrs);
            // 获取根视图
            final ViewGroup viewGroup = (ViewGroup) parent;
            // 获取根视图布局参数
            final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
            // Inflate子视图
            rInflateChildren(parser, view, attrs, true);
            // 添加子视图
            viewGroup.addView(view, params);
        }
    }
    if (finishInflate) {
        parent.onFinishInflate();
    }
}