通过XML创建View的原理

短命女 2022-05-27 04:38 166阅读 0赞

转载请注明链接：[https://blog.csdn.net/feather\_wch/article/details/79900081][https_blog.csdn.net_feather_wch_article_details_79900081]

本文详细分析从XML创建View的原理

# 通过XML创建View的原理 #

版本：2018/8/27-1

--------------------

*  通过XML创建View的原理
    
     *  原理
     *  OnCreate流程
     *  setContentView流程
     *  换肤中的应用
     *  知识储备
     *  学习和参考资料

## 原理 ##

本质原理：  
1. Activity是通过`Factory`进行View的创建  
2. 自定义`Factory`就能拦截创建过程，创建自己的`View`

## OnCreate流程 ##

1、AppCompatActivity的OnCreate流程

//AppCompatActivity.java
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        final AppCompatDelegate delegate = getDelegate();
        //1. 初始化LayoutInflater，并且设置过Factory(没有设置过就新建)
        delegate.installViewFactory();
        //2. 执行正常的onCreate流程
        delegate.onCreate(savedInstanceState);
        //xxx
        super.onCreate(savedInstanceState);
    }
    //AppCompatDelegateImpV9.java
    public void installViewFactory() {
        LayoutInflater layoutInflater = LayoutInflater.from(mContext);
        //1. 没有Factory,系统会创建一个Factory去进行XML到View的转换
        if (layoutInflater.getFactory() == null) {
            LayoutInflaterCompat.setFactory2(layoutInflater, this);
        } else {
            if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImplV9)) {
                Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed" + " so we can not install AppCompat's");
            }
        }
    }
    //LayoutInflaterCompat.java
    public static void setFactory2(@NonNull LayoutInflater inflater, @NonNull LayoutInflater.Factory2 factory) {
        //1. 能将Factory接口绑定到创建View的LayoutInflater(IMPL类型为LayoutInflaterCompatBaseImpl)
        IMPL.setFactory2(inflater, factory);
    }
    //LayoutInflaterCompat.java内部类LayoutInflaterCompatBaseImpl:
    static class LayoutInflaterCompatBaseImpl {
        //xxx
        public void setFactory2(LayoutInflater inflater, LayoutInflater.Factory2 factory) {
            inflater.setFactory2(factory);
            //xxx
        }
    }
    //LayoutInflater.java-完成Factory的创建
    public void setFactory2(Factory2 factory) {
        //xxx
        if (mFactory == null) {
            mFactory = mFactory2 = factory;
        } else {
            mFactory = mFactory2 = new FactoryMerger(factory, factory, mFactory, mFactory2);
        }
    }

## setContentView流程 ##

2、AppCompatActivity的OnCreate中setContentView()的流程

//AppCompatDelegateImplV9.java
        public void setContentView(int resId) {
            //xxx
            //1. 获取到父容器Content
            ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
            contentParent.removeAllViews();
            //2. 通过LayoutInflater加载布局文件
            LayoutInflater.from(mContext).inflate(resId, contentParent);
            mOriginalWindowCallback.onContentChanged();
        }
    
    //LayoutInlfater.java
        public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
            return inflate(resource, root, root != null);
        }
    
    //LayoutInlfater.java
        public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
            final Resources res = getContext().getResources();
            //xxx
            final XmlResourceParser parser = res.getLayout(resource);
            //1. 重点
            return inflate(parser, root, attachToRoot);
        }
    //LayoutInlfater.java
        public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
            ...
            final String name = parser.getName();//控件名
            //1. 将XmlPullParser转换为View的属性AttributeSet,给其他方法使用
            final AttributeSet attrs = Xml.asAttributeSet(parser);
            //2. Temp是XML文件中的根布局(name为"LinearLayout"等等)
            final View temp = createViewFromTag(root, name, inflaterContext, attrs);
            //3. 将XML根布局中temp下面所有的子View都进行加载
            rInflateChildren(parser, temp, attrs, true);
            //4. 将根布局tmp中找到的所有View贴到root中(content view)
            if (root != null && attachToRoot) {
                root.addView(temp, params);
            }
            ...
        }
    
    /**====================================== * 通过提供的属性AttributeSet attrs, 创建View * // LayoutInlfater.java *=======================================*/
        View createViewFromTag(View parent, String name, Context context, AttributeSet attrs, boolean ignoreThemeAttr) {
            //1. 彩蛋?<blink>标签会进行闪烁
            if (name.equals(TAG_1995)) {
                // Let's party like it's 1995!
                return new BlinkLayout(context, attrs);
            }
            //2. 通过Factory创建View
            View view;
            view = mFactory2.onCreateView(parent, name, context, attrs);
    
            //xxx
            return view;
        }
    
    //AppCompatDelegateImplV9.java
        public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
           ...
            //创建View
            return createView(parent, name, context, attrs);
        }
    //AppCompatDelegateImplV9.java
        public View createView(View parent, final String name, @NonNull Context context, @NonNull AttributeSet attrs) {
            ...
            return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,
                    IS_PRE_LOLLIPOP, /* Only read android:theme pre-L (L+ handles this anyway) */
                    true, /* Read read app:theme as a fallback at all times for legacy reasons */
                    VectorEnabledTintResources.shouldBeUsed() /* Only tint wrap the context if enabled */
            );
        }
    //AppCompatViewInflater.java-最终完成从XML到View的转变
        public final View createView(View parent, final String name, Context context, AttributeSet attrs, ...) {
    
            View view = null;
            switch (name) {
                case "TextView":
                    view = new AppCompatTextView(context, attrs);
                    break;
                case "ImageView":
                    view = new AppCompatImageView(context, attrs);
                    break;
                case "Button":
                    view = new AppCompatButton(context, attrs);
                    break;
                case "EditText":
                    view = new AppCompatEditText(context, attrs);
                    break;
                case "Spinner":
                    view = new AppCompatSpinner(context, attrs);
                    break;
                case "ImageButton":
                    view = new AppCompatImageButton(context, attrs);
                    break;
                case "CheckBox":
                    view = new AppCompatCheckBox(context, attrs);
                    break;
                case "RadioButton":
                    view = new AppCompatRadioButton(context, attrs);
                    break;
                case "CheckedTextView":
                    view = new AppCompatCheckedTextView(context, attrs);
                    break;
                case "AutoCompleteTextView":
                    view = new AppCompatAutoCompleteTextView(context, attrs);
                    break;
                case "MultiAutoCompleteTextView":
                    view = new AppCompatMultiAutoCompleteTextView(context, attrs);
                    break;
                case "RatingBar":
                    view = new AppCompatRatingBar(context, attrs);
                    break;
                case "SeekBar":
                    view = new AppCompatSeekBar(context, attrs);
                    break;
            }
            ...
            return view;
        }

## 换肤中的应用 ##

3、自定义Activity中通过Factory对控件的创建进行拦截，实现“换肤”效果：

public class SkinActivity extends AppCompatActivity{ 
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
    
            LayoutInflaterCompat.setFactory2(LayoutInflater.from(this), new LayoutInflater.Factory2() {
                @Override
                public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
                    AppCompatDelegate delegate = getDelegate();
                    View view = delegate.createView(parent, name, context, attrs);
                    return view;
                }
    
                @Override
                public View onCreateView(String name, Context context, AttributeSet attrs) {
                    View view = null;
                    switch (name) {
                        case "TextView":
                            view = new AppCompatTextView(context, attrs);
                            break;
                        case "ImageView":
                            view = new AppCompatImageView(context, attrs);
                            break;
                        case "Button":
                            view = new AppCompatButton(context, attrs);
                            break;
                        case "EditText":
                            view = new AppCompatEditText(context, attrs);
                            break;
                        //...
                    }
                    return view;
                }
            });
        }
    }

## 知识储备 ##

1、开源协议有哪些？  
![授权图][3e5cb4629d991c4b826788fe3e2877e5_hd.jpg]

## 学习和参考资料 ##

1.  [ Android 探究 LayoutInflater setFactory][Android _ LayoutInflater setFactory]
2.  [Github:Android-Skin(换肤库)][Github_Android-Skin]

[https_blog.csdn.net_feather_wch_article_details_79900081]: https://blog.csdn.net/feather_wch/article/details/79900081
[3e5cb4629d991c4b826788fe3e2877e5_hd.jpg]: /images/20220527/2c57f627702a4d409bba72f601d5c49c.png
[Android _ LayoutInflater setFactory]: https://blog.csdn.net/lmj623565791/article/details/51503977
[Github_Android-Skin]: https://github.com/MeetYouDevs/Android-Skin