LayoutInflater 加载布局文件源码

LayoutInflater是一个用于将xml布局文件加载为View或者ViewGroup对象的工具，我们可以称之为布局加载器。

获取LayoutInflater实例

有3种方式获取到取LayoutInflater实例

第一种

(LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
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第二种 是针对第一种的封装

LayoutInflater.from(context); 复制代码

第三种 在Activity中，封装了获取LayoutInflater的接口

Activity.getLayoutInflater()
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LayoutInflater 的使用创建View

创建View，有4个重载方式

• inflate(int resource, ViewGroup root)
• inflate(int resource, ViewGroup root, boolean attachToRoot)
• inflate(XmlPullParser parser, ViewGroup root)
• inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)

一般常用的是前2种

源码解析

LayoutInflate
|
|-inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot)||-final View temp = createViewFromTag(root, name, inflaterContext, attrs); 创建根节点View||-if(root != nul) root.generateLayoutParams(attrs);|根据根节点属性创建，根节点View的LayoutParams||-if(!attachToRoot) temp.setLayoutParams(params); |如果添加到rootView，设置布局文件根View的LayoutParams属性||- rInflateChildren(parser, temp, attrs, true);|加载布局文件中子View||-if (root != null && attachToRoot) root.addView(temp, params);|将布局文件中根节点View添加到rootView中这里解释了，inflate重载方法中root和attachToRoot这两个参数的含义LayoutInflate
|
|-View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,boolean ignoreThemeAttr)
|根据布局文件节点名称创建View|||-if (mFactory2 != null) view = mFactory2.onCreateView(parent, name, context, attrs);|1.优先mFactory2创建view||-if (mFactory != null)  view = mFactory.onCreateView(name, context, attrs);|2.mFactory创建view||-if (view == null && mPrivateFactory != null)  view = mPrivateFactory.onCreateView(parent, name, context, attrs);|3.mPrivateFactory创建view||-view = createView(name, null, attrs);|4.直接通过反射方式创建View||-clazz = mContext.getClassLoader().loadClass(prefix != null ? (prefix + name) : name).asSubclass(View.class);|-constructor = clazz.getConstructor(mConstructorSignature);|-final View view = constructor.newInstance(args);|通过反射创建View如果继承自AppCompateActivity，mFactory2!=null，创建AppCompateTextView，等对象LayoutInflate
|
|-rInflateChildren(parser, temp, attrs, true);
|加载子View||-final View view = createViewFromTag(parent, name, context, attrs);|创建子View||-final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);|生成子View LayoutParmas属性||-rInflateChildren(parser, view, attrs, true);|创建该节点下子View||-viewGroup.addView(view, params);|将子View添加到父View中||-if (finishInflate) parent.onFinishInflate();|结束递归rInflateChildrenrInflateChildren函数是一个根据布局文件的节点递归遍历生生成子View，并添加到View树中，
当某个节点下面的所有子节点View解析生成完成后，才会调起onFinishInflate回调复制代码

利用LayoutInflate替换布局文件中默认View

1. 实现LayoutInflater.Factory2接口

public class TestLayoutFactory implements LayoutInflater.Factory2 {private static final String TAG = "TestLayoutFactory";private final AppCompatDelegate delegate;public TestLayoutFactory(AppCompatDelegate delegate) {this.delegate = delegate;}@Overridepublic View onCreateView(View parent, String name, Context context, AttributeSet attrs) {if (TextUtils.equals("TextView", name)) {return new CustomTextView(context, attrs);}return delegate.createView(parent, name, context, attrs);}@Overridepublic View onCreateView(String name, Context context, AttributeSet attrs) {return null;}
}
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1. 在AppCompatActivity的onCreate()方法中设置LayoutInfalte.Factory

    override fun onCreate(savedInstanceState: Bundle?) {LayoutInflaterCompat.setFactory2(layoutInflater, TestLayoutFactory(getDelegate()))super.onCreate(savedInstanceState)setContentView(R.layout.activity_test_layout_factory)}
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一定要在super.onCreate(savedInstanceState) 代码之前设置，否则会报错：

Caused by: java.lang.IllegalStateException: A factory has already been set on this LayoutInflater
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因为在调用父类的onCreate()方法中，已经创建了LayoutInfalte.Factory，再次创建的时候，就会报错了