Android LayoutInflater的用法详解

2023-10-22 13:50

本文主要是介绍Android LayoutInflater的用法详解,希望对大家解决编程问题提供一定的参考价值,需要的开发者们随着小编来一起学习吧!

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. Throws
342     * {@link InflateException} if there is an error.
343     *
344     * @param resource ID for an XML layout resource to load (e.g.,
345     *        <code>R.layout.main_page</code>)
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 inflated
349     *         XML file.
350     */
351    public View inflate(int resource, ViewGroup root) {
352        return inflate(resource, root, root != null);
353    }
354
355    /**
356     * Inflate a new view hierarchy from the specified xml node. Throws
357     * {@link InflateException} if there is an error. *
358     * <p>
359     * <em><strong>Important</strong></em>&nbsp;&nbsp;&nbsp;For performance
360     * reasons, view inflation relies heavily on pre-processing of XML files
361     * that is done at build time. Therefore, it is not currently possible to
362     * use LayoutInflater with an XmlPullParser over a plain XML file at runtime.
363     *
364     * @param parser XML dom node containing the description of the view
365     *        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 inflated
369     *         XML file.
370     */
371    public View inflate(XmlPullParser parser, ViewGroup root) {
372        return inflate(parser, root, root != null);
373    }
374
375    /**
376     * Inflate a new view hierarchy from the specified xml resource. Throws
377     * {@link InflateException} if there is an error.
378     *
379     * @param resource ID for an XML layout resource to load (e.g.,
380     *        <code>R.layout.main_page</code>)
381     * @param root Optional view to be the parent of the generated hierarchy (if
382     *        <em>attachToRoot</em> is true), or else simply an object that
383     *        provides a set of LayoutParams values for root of the returned
384     *        hierarchy (if <em>attachToRoot</em> is false.)
385     * @param attachToRoot Whether the inflated hierarchy should be attached to
386     *        the root parameter? If false, root is only used to create the
387     *        correct subclass of LayoutParams for the root view in the XML.
388     * @return The root View of the inflated hierarchy. If root was supplied and
389     *         attachToRoot is true, this is root; otherwise it is the root of
390     *         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. Throws
404     * {@link InflateException} if there is an error.
405     * <p>
406     * <em><strong>Important</strong></em>&nbsp;&nbsp;&nbsp;For performance
407     * reasons, view inflation relies heavily on pre-processing of XML files
408     * that is done at build time. Therefore, it is not currently possible to
409     * use LayoutInflater with an XmlPullParser over a plain XML file at runtime.
410     *
411     * @param parser XML dom node containing the description of the view
412     *        hierarchy.
413     * @param root Optional view to be the parent of the generated hierarchy (if
414     *        <em>attachToRoot</em> is true), or else simply an object that
415     *        provides a set of LayoutParams values for root of the returned
416     *        hierarchy (if <em>attachToRoot</em> is false.)
417     * @param attachToRoot Whether the inflated hierarchy should be attached to
418     *        the root parameter? If false, root is only used to create the
419     *        correct subclass of LayoutParams for the root view in the XML.
420     * @return The root View of the inflated hierarchy. If root was supplied and
421     *         attachToRoot is true, this is root; otherwise it is the root of
422     *         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;
430
431            try {
432                // Look for the root node.
433                int type;
434                while ((type = parser.next()) != XmlPullParser.START_TAG &&
435                        type != XmlPullParser.END_DOCUMENT) {
436                    // Empty
437                }
438
439                if (type != XmlPullParser.START_TAG) {
440                    throw new InflateException(parser.getPositionDescription()
441                            + ": No start tag found!");
442                }
443
444                final String name = parser.getName();
445
446                if (DEBUG) {
447                    System.out.println("**************************");
448                    System.out.println("Creating root view: "
449                            + name);
450                    System.out.println("**************************");
451                }
452
453                if (TAG_MERGE.equals(name)) {
454                    if (root == null || !attachToRoot) {
455                        throw new InflateException("<merge /> can be used only with a valid "
456                                + "ViewGroup root and attachToRoot=true");
457                    }
458
459                    rInflate(parser, root, attrs, false);
460                } else {
461                    // Temp is the root view that was found in the xml
462                    View temp;
463                    if (TAG_1995.equals(name)) {
464                        temp = new BlinkLayout(mContext, attrs);
465                    } else {
466                        temp = createViewFromTag(root, name, attrs);
467                    }
468
469                    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LayoutParams
478                        if (!attachToRoot) {
479                            // Set the layout params for temp if we are not
480                            // attaching. (If we are, we use addView, below)
481                            temp.setLayoutParams(params);
482                        }
483                    }
484
485                    if (DEBUG) {
486                        System.out.println("-----> start inflating children");
487                    }
488                    // Inflate all children under temp
489                    rInflate(parser, temp, attrs, true);
490                    if (DEBUG) {
491                        System.out.println("-----> done inflating children");
492                    }
493
494                    // 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                    }
499
500                    // Decide whether to return the root that was passed in or the
501                    // 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                }
506
507            } 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 result
523            return result;
524        }
525    }

由上源码我们可以得出:
inflate(layout, null)返回的是View本身,addView后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add到父层并为该View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父层不会addView。
inflate(layout, parent, true)同第三个方法一样,父层View会addView并为其设置参数。

这篇关于Android LayoutInflater的用法详解的文章就介绍到这儿,希望我们推荐的文章对编程师们有所帮助!



http://www.chinasem.cn/article/261845

相关文章

Conda与Python venv虚拟环境的区别与使用方法详解

《Conda与Pythonvenv虚拟环境的区别与使用方法详解》随着Python社区的成长,虚拟环境的概念和技术也在不断发展,:本文主要介绍Conda与Pythonvenv虚拟环境的区别与使用... 目录前言一、Conda 与 python venv 的核心区别1. Conda 的特点2. Python v

Spring Boot中WebSocket常用使用方法详解

《SpringBoot中WebSocket常用使用方法详解》本文从WebSocket的基础概念出发,详细介绍了SpringBoot集成WebSocket的步骤,并重点讲解了常用的使用方法,包括简单消... 目录一、WebSocket基础概念1.1 什么是WebSocket1.2 WebSocket与HTTP

java中反射Reflection的4个作用详解

《java中反射Reflection的4个作用详解》反射Reflection是Java等编程语言中的一个重要特性,它允许程序在运行时进行自我检查和对内部成员(如字段、方法、类等)的操作,本文将详细介绍... 目录作用1、在运行时判断任意一个对象所属的类作用2、在运行时构造任意一个类的对象作用3、在运行时判断

MySQL 中的 CAST 函数详解及常见用法

《MySQL中的CAST函数详解及常见用法》CAST函数是MySQL中用于数据类型转换的重要函数,它允许你将一个值从一种数据类型转换为另一种数据类型,本文给大家介绍MySQL中的CAST... 目录mysql 中的 CAST 函数详解一、基本语法二、支持的数据类型三、常见用法示例1. 字符串转数字2. 数字

SpringBoot中SM2公钥加密、私钥解密的实现示例详解

《SpringBoot中SM2公钥加密、私钥解密的实现示例详解》本文介绍了如何在SpringBoot项目中实现SM2公钥加密和私钥解密的功能,通过使用Hutool库和BouncyCastle依赖,简化... 目录一、前言1、加密信息(示例)2、加密结果(示例)二、实现代码1、yml文件配置2、创建SM2工具

MyBatis-Plus 中 nested() 与 and() 方法详解(最佳实践场景)

《MyBatis-Plus中nested()与and()方法详解(最佳实践场景)》在MyBatis-Plus的条件构造器中,nested()和and()都是用于构建复杂查询条件的关键方法,但... 目录MyBATis-Plus 中nested()与and()方法详解一、核心区别对比二、方法详解1.and()

Python中你不知道的gzip高级用法分享

《Python中你不知道的gzip高级用法分享》在当今大数据时代,数据存储和传输成本已成为每个开发者必须考虑的问题,Python内置的gzip模块提供了一种简单高效的解决方案,下面小编就来和大家详细讲... 目录前言:为什么数据压缩如此重要1. gzip 模块基础介绍2. 基本压缩与解压缩操作2.1 压缩文

Spring IoC 容器的使用详解(最新整理)

《SpringIoC容器的使用详解(最新整理)》文章介绍了Spring框架中的应用分层思想与IoC容器原理,通过分层解耦业务逻辑、数据访问等模块,IoC容器利用@Component注解管理Bean... 目录1. 应用分层2. IoC 的介绍3. IoC 容器的使用3.1. bean 的存储3.2. 方法注

MySQL 删除数据详解(最新整理)

《MySQL删除数据详解(最新整理)》:本文主要介绍MySQL删除数据的相关知识,本文通过实例代码给大家介绍的非常详细,对大家的学习或工作具有一定的参考借鉴价值,需要的朋友参考下吧... 目录一、前言二、mysql 中的三种删除方式1.DELETE语句✅ 基本语法: 示例:2.TRUNCATE语句✅ 基本语

Python内置函数之classmethod函数使用详解

《Python内置函数之classmethod函数使用详解》:本文主要介绍Python内置函数之classmethod函数使用方式,具有很好的参考价值,希望对大家有所帮助,如有错误或未考虑完全的地... 目录1. 类方法定义与基本语法2. 类方法 vs 实例方法 vs 静态方法3. 核心特性与用法(1编程客