相信我们在开发过程中肯定接触过LayoutInflater，比如ListView的适配器里的getView方法里通过LayoutInflater.from(Context).inflater来加载xml布局，在Fragment里的onCreateView里面也是一样，加载布局一共三种方法。

1，在Activity里面调用getLayoutInflater() 2, 通过LayoutInflater.from(context).inflater() 3, context.getSystemService(Context.LAYOUT_INFLATER_SERVICE)) 以上的三种方式从实现上都是一样的，Activity里面的getLayoutInflater()实际上调用的是PhoneWindow的实现，而PhoneWindow里源码的处理是LayoutInflater.from(context).inflater()，往下查找最终调用context.getSystemService。 context.getSystemService是Android里一个比较重要的api，是Activity的一个方法，根据传入的Name来取得对应的Object，然后转换成相应的服务对象。以下是系统相应的服务。 传入的Name返回的对象说明 WINDOW_SERVICE WindowManager 管理打开的窗口程序 LAYOUT_INFLATER_SERVICE LayoutInflater 取得xml里定义的view ACTIVITY_SERVICE ActivityManager 管理应用程序的系统状态 POWER_SERVICE PowerManger 电源的服务 ALARM_SERVICE AlarmManager 闹钟的服务 NOTIFICATION_SERVICE NotificationManager 状态栏的服务 KEYGUARD_SERVICE KeyguardManager 键盘锁的服务 LOCATION_SERVICE LocationManager 位置的服务，如GPS SEARCH_SERVICE SearchManager 搜索的服务 VEBRATOR_SERVICE Vebrator 手机震动的服务 CONNECTIVITY_SERVICE Connectivity 网络连接的服务 WIFI_SERVICE WifiManager Wi-Fi服务 TELEPHONY_SERVICE TeleponyManager 电话服务

但是LayoutInflater.from(context).inflater()的方法这么多，那它们到底是什么样的用法呢？

/**341     * Inflate a new view hierarchy from the specified xml resource. Throws342     * {@link InflateException} if there is an error.343     *344     * @param resource ID for an XML layout resource to load (e.g.,345     *        R.layout.main_page)346     * @param root Optional view to be the parent of the generated hierarchy.347     * @return The root View of the inflated hierarchy. If root was supplied,348     *         this is the root View; otherwise it is the root of the inflated349     *         XML file.350     */351    public View inflate(int resource, ViewGroup root) {352        return inflate(resource, root, root != null);353    }354355    /**356     * Inflate a new view hierarchy from the specified xml node. Throws357     * {@link InflateException} if there is an error. *358     * 
359     * Important   For performance360     * reasons, view inflation relies heavily on pre-processing of XML files361     * that is done at build time. Therefore, it is not currently possible to362     * use LayoutInflater with an XmlPullParser over a plain XML file at runtime.363     *364     * @param parser XML dom node containing the description of the view365     *        hierarchy.366     * @param root Optional view to be the parent of the generated hierarchy.367     * @return The root View of the inflated hierarchy. If root was supplied,368     *         this is the root View; otherwise it is the root of the inflated369     *         XML file.370     */371    public View inflate(XmlPullParser parser, ViewGroup root) {372        return inflate(parser, root, root != null);373    }374375    /**376     * Inflate a new view hierarchy from the specified xml resource. Throws377     * {@link InflateException} if there is an error.378     *379     * @param resource ID for an XML layout resource to load (e.g.,380     *        R.layout.main_page)381     * @param root Optional view to be the parent of the generated hierarchy (if382     *        attachToRoot is true), or else simply an object that383     *        provides a set of LayoutParams values for root of the returned384     *        hierarchy (if attachToRoot is false.)385     * @param attachToRoot Whether the inflated hierarchy should be attached to386     *        the root parameter? If false, root is only used to create the387     *        correct subclass of LayoutParams for the root view in the XML.388     * @return The root View of the inflated hierarchy. If root was supplied and389     *         attachToRoot is true, this is root; otherwise it is the root of390     *         the inflated XML file.391     */392    public View inflate(int resource, ViewGroup root, boolean attachToRoot) {393        if (DEBUG) System.out.println("INFLATING from resource: " + resource);394        XmlResourceParser parser = getContext().getResources().getLayout(resource);395        try {396            return inflate(parser, root, attachToRoot);397        } finally {398            parser.close();399        }400    }

上面的方法非常清晰，直接看下inflate(parser, root, attachToRoot);

/**403     * Inflate a new view hierarchy from the specified XML node. Throws404     * {@link InflateException} if there is an error.405     * 
406     * Important   For performance407     * reasons, view inflation relies heavily on pre-processing of XML files408     * that is done at build time. Therefore, it is not currently possible to409     * use LayoutInflater with an XmlPullParser over a plain XML file at runtime.410     *411     * @param parser XML dom node containing the description of the view412     *        hierarchy.413     * @param root Optional view to be the parent of the generated hierarchy (if414     *        attachToRoot is true), or else simply an object that415     *        provides a set of LayoutParams values for root of the returned416     *        hierarchy (if attachToRoot is false.)417     * @param attachToRoot Whether the inflated hierarchy should be attached to418     *        the root parameter? If false, root is only used to create the419     *        correct subclass of LayoutParams for the root view in the XML.420     * @return The root View of the inflated hierarchy. If root was supplied and421     *         attachToRoot is true, this is root; otherwise it is the root of422     *         the inflated XML file.423     */424    public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {425        synchronized (mConstructorArgs) {426            final AttributeSet attrs = Xml.asAttributeSet(parser);427            Context lastContext = (Context)mConstructorArgs[0];428            mConstructorArgs[0] = mContext;429            View result = root;430431            try {432                // Look for the root node.433                int type;434                while ((type = parser.next()) != XmlPullParser.START_TAG &&435                        type != XmlPullParser.END_DOCUMENT) {436                    // Empty437                }438439                if (type != XmlPullParser.START_TAG) {440                    throw new InflateException(parser.getPositionDescription()441                            + ": No start tag found!");442                }443444                final String name = parser.getName();445446                if (DEBUG) {447                    System.out.println("**************************");448                    System.out.println("Creating root view: "449                            + name);450                    System.out.println("**************************");451                }452453                if (TAG_MERGE.equals(name)) {454                    if (root == null || !attachToRoot) {455                        throw new InflateException("
       can be used only with a valid "456                                + "ViewGroup root and attachToRoot=true");457                    }458459                    rInflate(parser, root, attrs, false);460                } else {461                    // Temp is the root view that was found in the xml462                    View temp;463                    if (TAG_1995.equals(name)) {464                        temp = new BlinkLayout(mContext, attrs);465                    } else {466                        temp = createViewFromTag(root, name, attrs);467                    }468469                    ViewGroup.LayoutParams params = null;470                    // 当父层不为空时471                    if (root != null) {472                        if (DEBUG) {473                            System.out.println("Creating params from root: " +474                                    root);475                        }476                        // Create layout params that match root, if supplied                              // 获取父层的参数并赋值477                        params = root.generateLayoutParams(attrs);                              //  子布局不贴上也会被设置LayoutParams478                        if (!attachToRoot) {479                            // Set the layout params for temp if we are not480                            // attaching. (If we are, we use addView, below)481                            temp.setLayoutParams(params);482                        }483                    }484485                    if (DEBUG) {486                        System.out.println("-----> start inflating children");487                    }488                    // Inflate all children under temp489                    rInflate(parser, temp, attrs, true);490                    if (DEBUG) {491                        System.out.println("-----> done inflating children");492                    }493494                    // We are supposed to attach all the views we found (int temp)495                    // to root. Do that now.                          // 父布局不为空并且贴上会被add到父层496                    if (root != null && attachToRoot) {497                        root.addView(temp, params);498                    }499500                    // Decide whether to return the root that was passed in or the501                    // top view found in xml.                          // 父布局为空或者没有贴上，result就是View本身502                    if (root == null || !attachToRoot) {503                        result = temp;504                    }505                }506507            } catch (XmlPullParserException e) {508                InflateException ex = new InflateException(e.getMessage());509                ex.initCause(e);510                throw ex;511            } catch (IOException e) {512                InflateException ex = new InflateException(513                        parser.getPositionDescription()514                        + ": " + e.getMessage());515                ex.initCause(e);516                throw ex;517            } finally {518                // Don't retain static reference on context.519                mConstructorArgs[0] = lastContext;520                mConstructorArgs[1] = null;521            }522          // 最后返回 result523            return result;524        }525    }

由上源码我们可以得出：

inflate(layout, null)返回的是View本身，且View本身所设置的布局参数无效，由父层和子View决定大小。 inflate(layout, null, false)同上一样，当父层为空，第三个值是否为真没有意义 inflate(layout, parent)子布局会被加入到父层并设置布局参数，具体大小由父层和子View决定 inflate(layout, parent, false)同上一样，区别就是false返回的是子View本身。 inflate(layout, parent, true)同第三个方法一样，返回父层View