AppcompatActivity拦截View创建方法

FragementActivity&AppcompatActivity拦截View创建方法

在拦截之前,我们要先清楚 系统是怎么创建各个View的,如果看过LayoutInflate的源码的话,可能这部分就比较容易理解

本文源码版本: API 25

1 LayoutInflater创建一个View的过程

LayoutInflater inflater = LayoutInflater.from(context).inflate(LayoutResId,ViewRoot);

大家一定用过上面这行代码,这行代码在ListView或者RecycleView中尤为常见,那么系统是如何将这个layout文件变成View的呢?还记得setContentView(LayoutResId)么,Activity在加载这个View的时候是不是一样呢?

• LayoutInflater.inflate

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {        return inflate(resource, root, root != null);} public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {        //获取Resources对象        final Resources res = getContext().getResources();        //拿到 一个layout文件的 解析器        final XmlResourceParser parser = res.getLayout(resource);        try {            return inflate(parser, root, attachToRoot);        } finally {            parser.close();        } }  //我删除了一部分代码,其实这里主要就是 对xml文件的解析public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {        synchronized (mConstructorArgs) {            //这部分代码很值得借鉴,            final Context inflaterContext = mContext;            //获取root节点的属性,这里就不进去看了,咱们关注的重点不在这里            final AttributeSet attrs = Xml.asAttributeSet(parser);            Context lastContext = (Context) mConstructorArgs[0];            // new View(Context context,AttributeSet attr)            //这个参数就是 context            mConstructorArgs[0] = inflaterContext;            View result = root;            try {                final String name = parser.getName();                if (TAG_MERGE.equals(name)) {                    //这里是 marge标签的处理哟,marge标签不需要创建                    if (root == null || !attachToRoot) {                        throw new InflateException("<merge /> can be used only with a valid "                                + "ViewGroup root and attachToRoot=true");                    }                    //递归处理直接点的View,其实最后真正创建View还是走的createViewFromTag方法                    rInflate(parser, root, inflaterContext, attrs, false);                } else {                    //这里是rootView的处理,第一个节点的处理                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);                    ViewGroup.LayoutParams params = null;                    if (root != null) {                        //为rootView创建LayoutParams                        params = root.generateLayoutParams(attrs);                        if (!attachToRoot) {                            // Set the layout params for temp if we are not                            // attaching. (If we are, we use addView, below)                            temp.setLayoutParams(params);                        }                    }                    // 创建子节点的View                    rInflateChildren(parser, temp, attrs, true);                    ....                }            } catch (XmlPullParserException e) {            } catch (Exception e) {            } finally {                mConstructorArgs[0] = lastContext;                mConstructorArgs[1] = null;            }            return result;        }    }

以上是处理 layout.xml文件的方式,下面来看 真正创建View的方法

  private View createViewFromTag(View parent, String name, Context context, AttributeSet attrs) {        return createViewFromTag(parent, name, context, attrs, false);    }//同样省略一些代码View createViewFromTag(View parent, String name, Context context, AttributeSet attrs, boolean ignoreThemeAttr) {        if (name.equals("view")) {            name = attrs.getAttributeValue(null, "class");        }        // 应用主题...省略        try {            View view;            //factory 咱们关心的重点            if (mFactory2 != null) {                view = mFactory2.onCreateView(parent, name, context, attrs);            } else if (mFactory != null) {                view = mFactory.onCreateView(name, context, attrs);            } else {                view = null;            }            if (view == null && mPrivateFactory != null) {                view = mPrivateFactory.onCreateView(parent, name, context, attrs);            }            if (view == null) {                final Object lastContext = mConstructorArgs[0];                mConstructorArgs[0] = context;                try {                    if (-1 == name.indexOf('.')) {                        //是系统的View,前面没有包名                        view = onCreateView(parent, name, attrs);                    } else {                        view = createView(name, null, attrs);                    }                } finally {                    mConstructorArgs[0] = lastContext;                }            }            return view;        } catch (InflateException e) {        } catch (ClassNotFoundException e) {        } catch (Exception e) {        }    }

从上面可以看出,只有当factory不为空的时候,并且创建View没有成功的时候,才会走下面的createView和onCreateView,那么factory是什么,其实看起来更像是一个过滤器,为什么有factory和factory2呢,因为版本兼容.
这里的分析到这里为止,我简单说下createView和onCreateView 里面的逻辑

onCreateView 创建系统自带的View

createView 创建自定义的View

2 AppcompatActivity

要想拦截 AppcompatActivity 创建View的过程,可以用下面的方法来做,其实就是给LayoutInflate重新设置factory

ublic class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        LayoutInflater inflater = LayoutInflater.from(this);        LayoutInflaterCompat.setFactory(inflater, new LayoutInflaterFactory() {            @Override            public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {                return null;            }        });        setContentView(R.layout.activity_main);    }

这个时候,我们就要明白AppCompatActivity 有没有用factory,我们只是添加自己的逻辑,进行拦截修改,而不是完全重写,所以这里我们要先完成AppCompatActivity 所做的事情,然后拿到View之后再做处理,当然也可以在之前做处理

我们来看AppCompatActivity是怎么创建View的

• AppCompatActivity

private AppCompatDelegate mDelegate; @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        final AppCompatDelegate delegate = getDelegate();        //在这里初始化了factory        delegate.installViewFactory();        ....    }

AppCompatDelegate是一个抽象方法,installViewFactory也是一个抽象方法

public abstract class AppCompatDelegate public abstract void installViewFactory();

ctrl+shift+h,我们来看这个方法在哪里实现了

上面的图很有意思,可以看到google为了兼容做的处理

• AppCompatDelegateImplV9 实现 了这个方法

@Override    public void installViewFactory() {        LayoutInflater layoutInflater = LayoutInflater.from(mContext);        if (layoutInflater.getFactory() == null) {            //factory是本身            LayoutInflaterCompat.setFactory(layoutInflater, this);        } else {           //已经设置了factory,并且不是本类的实现,那么不做任何处理        }    }

那么我们去看重写的createView方法

 /**     * From {@link android.support.v4.view.LayoutInflaterFactory}     */    @Override    public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {        // First let the Activity's Factory try and inflate the view        //首先使用activity的factory去加载view        final View view = callActivityOnCreateView(parent, name, context, attrs);        if (view != null) {            return view;        }        // 如果activity的factory没有创建这个View        return createView(parent, name, context, attrs);    } @Override    public View createView(View parent, final String name, @NonNull Context context,            @NonNull AttributeSet attrs) {        if (mAppCompatViewInflater == null) {            mAppCompatViewInflater = new AppCompatViewInflater();        }        ....        return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,        );    }

上面还不是创建的方法,

• mAppCompatViewInflater.java

public final View createView(View parent, final String name, @NonNull Context context,        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;        }        if (view == null && originalContext != context) {            // If the original context does not equal our themed context, then we need to manually            // inflate it using the name so that android:theme takes effect.            view = createViewFromTag(context, name, attrs);        }        if (view != null) {            // If we have created a view, check it's android:onClick            checkOnClickListener(view, attrs);        }        return view;    }

从上面就可以看到 我们其实创建的一些View被系统替换成了AppcompatView,好吧,为了兼容

上面都是一些系统提供的View,然后又转入了 createViewFromTag的方法,之后的事情就是咱们再第一个模块说的事情了

那么我们如何拦截呢,其实很简单,通过反射,调用delegate的createView方法

 LayoutInflaterCompat.setFactory(inflater, new LayoutInflaterFactory() {            @Override            public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {                //之前做什么事情                View view=null;                AppCompatDelegate delegate = getDelegate();                try {                    Method createViewFd = delegate.getClass().getMethod("createView", View.class, String.class, Context.class, AttributeSet.class);                    createViewFd.setAccessible(true);                    view = (View) createViewFd.invoke(delegate, new Object[]{parent, name, context, attrs});                } catch (NoSuchMethodException e) {                    e.printStackTrace();                } catch (InvocationTargetException e) {                    e.printStackTrace();                } catch (IllegalAccessException e) {                    e.printStackTrace();                }                if(view==null){                }                //之后做什么事情                return view;            }        });

我看张弘洋的视屏说,上面的过程只是针对特定的View,虽然我没有找到相关的代码判断在那里,这里还是做一下处理,其实就是复制两个方法,然后我们单开一个类

public class MyLayoutInflaterFactory implements LayoutInflaterFactory {    AppCompatDelegate delegate;    private static final Map<String, Constructor<? extends View>> sConstructorMap            = new ArrayMap<>();    private final Object[] mConstructorArgs = new Object[2];    private static final Class<?>[] sConstructorSignature = new Class[]{            Context.class, AttributeSet.class};    private static final String[] sClassPrefixList = {            "android.widget.",            "android.view.",            "android.webkit."    };    public MyLayoutInflaterFactory(AppCompatDelegate delegate) {        this.delegate = delegate;    }    @Override    public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {        //之前做什么事情        View view = null;        try {            Method createViewFd = delegate.getClass().getMethod("createView", View.class, String.class, Context.class, AttributeSet.class);            createViewFd.setAccessible(true);            view = (View) createViewFd.invoke(delegate, new Object[]{parent, name, context, attrs});        } catch (NoSuchMethodException e) {            e.printStackTrace();        } catch (InvocationTargetException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }        //我看张弘洋的视屏说,上面的过程只是针对特定的View,虽然我没有找到相关的代码判断在那里,这里还是做一下处理        if (view == null) {            createViewFromTag(context, name, attrs);        }        //之后做什么事情        return view;    }    private View createViewFromTag(Context context, String name, AttributeSet attrs) {        if (name.equals("view")) {            name = attrs.getAttributeValue(null, "class");        }        try {            mConstructorArgs[0] = context;            mConstructorArgs[1] = attrs;            if (-1 == name.indexOf('.')) {                for (int i = 0; i < sClassPrefixList.length; i++) {                    final View view = createView(context, name, sClassPrefixList[i]);                    if (view != null) {                        return view;                    }                }                return null;            } else {                return createView(context, name, null);            }        } catch (Exception e) {            // We do not want to catch these, lets return null and let the actual LayoutInflater            // try            return null;        } finally {            // Don't retain references on context.            mConstructorArgs[0] = null;            mConstructorArgs[1] = null;        }    }    private View createView(Context context, String name, String prefix)            throws ClassNotFoundException, InflateException {        Constructor<? extends View> constructor = sConstructorMap.get(name);        try {            if (constructor == null) {                // Class not found in the cache, see if it's real, and try to add it                Class<? extends View> clazz = context.getClassLoader().loadClass(                        prefix != null ? (prefix + name) : name).asSubclass(View.class);                constructor = clazz.getConstructor(sConstructorSignature);                sConstructorMap.put(name, constructor);            }            constructor.setAccessible(true);            return constructor.newInstance(mConstructorArgs);        } catch (Exception e) {            // We do not want to catch these, lets return null and let the actual LayoutInflater            // try            return null;        }    }

在mainAct中设置上就好

 @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        LayoutInflater inflater = LayoutInflater.from(this);        LayoutInflaterCompat.setFactory(inflater,new MyLayoutInflaterFactory(getDelegate()));        setContentView(R.layout.activity_main);    }