AppCompatActivity怎么对View做的拦截

淡淡的烟草味﹌ 2022-10-01 06:52 50阅读 0赞

## 1.AppCompatActivity对View偷偷做的替换 ##

布局文件

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".MainActivity" android:paddingLeft="20dp">
    
        <TextView android:id="@+id/textView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello World!" android:layout_marginTop="20dp"/>
    
        <ImageView android:id="@+id/imageView" android:layout_width="250dp" android:layout_height="250dp" android:src="@mipmap/ic_launcher" android:layout_marginTop="20dp"/>
    </LinearLayout>
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MainActivity的java代码

public class MainActivity extends AppCompatActivity {
        @ViewById(R.id.textView)
        TextView mTextView;
        @ViewById(R.id.imageView)
        ImageView mImageView;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            ViewUtils.inject(this);
            System.out.println("==============================");
            System.out.println(mTextView);
            System.out.println(mImageView);
        }
    }
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运行的结果

2019-04-16 14:58:04.708 15885-15885/? I/System.out: ==============================
    2019-04-16 14:58:04.709 15885-15885/? I/System.out: android.support.v7.widget.AppCompatTextView{c63b90 V.ED..C.. ......ID 0,0-0,0 #7f0800a8 app:id/textView}
    2019-04-16 14:58:04.709 15885-15885/? I/System.out: android.support.v7.widget.AppCompatImageView{bed6c89 V.ED..... ......ID 0,0-0,0 #7f080054 app:id/imageView}
    复制代码

`TextView`和`ImageView`被偷偷替换成了AppCompatTextView和AppCompatImageView

## 2.AppCompatActivity中onCreate方法 ##

protected void onCreate(@Nullable Bundle savedInstanceState) {
            final AppCompatDelegate delegate = getDelegate();
            delegate.installViewFactory();
            delegate.onCreate(savedInstanceState);
            if (delegate.applyDayNight() && mThemeId != 0) {
                // If DayNight has been applied, we need to re-apply the theme for
                // the changes to take effect. On API 23+, we should bypass
                // setTheme(), which will no-op if the theme ID is identical to the
                // current theme ID.
                if (Build.VERSION.SDK_INT >= 23) {
                    onApplyThemeResource(getTheme(), mThemeId, false);
                } else {
                    setTheme(mThemeId);
                }
            }
            super.onCreate(savedInstanceState);
    }
    复制代码

看看delegate是什么

private static AppCompatDelegate create(Context context, Window window, AppCompatCallback callback) {
            if (Build.VERSION.SDK_INT >= 24) {
                return new AppCompatDelegateImplN(context, window, callback);
            } else if (Build.VERSION.SDK_INT >= 23) {
                return new AppCompatDelegateImplV23(context, window, callback);
            } else {
                return new AppCompatDelegateImplV14(context, window, callback);
            }
    }
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由于`AppCompatDelegateImplN extends AppCompatDelegateImplV23`  
`AppCompatDelegateImplV23 extends AppCompatDelegateImplV14`  
`AppCompatDelegateImplV14 extends AppCompatDelegateImplV9`  
直接看AppCompatDelegateImplV9中的installViewFactory方法

public void installViewFactory() {
            LayoutInflater layoutInflater = LayoutInflater.from(mContext);
            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");
                }
            }
     }
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LayoutInflaterCompat.setFactory2方法.

public static void setFactory2( @NonNull LayoutInflater inflater, @NonNull LayoutInflater.Factory2 factory) {
            IMPL.setFactory2(inflater, factory);
    }
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public void setFactory2(LayoutInflater inflater, LayoutInflater.Factory2 factory) {
               inflater.setFactory2(factory);
    
               final LayoutInflater.Factory f = inflater.getFactory();
               if (f instanceof LayoutInflater.Factory2) {
                   // The merged factory is now set to getFactory(), but not getFactory2() (pre-v21).
                   // We will now try and force set the merged factory to mFactory2
                   forceSetFactory2(inflater, (LayoutInflater.Factory2) f);
               } else {
                   // Else, we will force set the original wrapped Factory2
                   forceSetFactory2(inflater, factory);
               }
           }
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很明显,给inflater设置了factory。根据[LayoutInflater创建View][LayoutInflater_View]这篇博文,设置factory后会回调createView方法,在此方法中做View创建等等拦截

public View createView(View parent, final String name, @NonNull Context context, @NonNull AttributeSet attrs) {
            if (mAppCompatViewInflater == null) {
                TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);
                String viewInflaterClassName =
                        a.getString(R.styleable.AppCompatTheme_viewInflaterClass);
                if ((viewInflaterClassName == null)
                        || AppCompatViewInflater.class.getName().equals(viewInflaterClassName)) {
                    // Either default class name or set explicitly to null. In both cases
                    // create the base inflater (no reflection)
                    mAppCompatViewInflater = new AppCompatViewInflater();
                } else {
                    try {
                        Class viewInflaterClass = Class.forName(viewInflaterClassName);
                        mAppCompatViewInflater =
                                (AppCompatViewInflater) viewInflaterClass.getDeclaredConstructor()
                                        .newInstance();
                    } catch (Throwable t) {
                        Log.i(TAG, "Failed to instantiate custom view inflater "
                                + viewInflaterClassName + ". Falling back to default.", t);
                        mAppCompatViewInflater = new AppCompatViewInflater();
                    }
                }
            }
    
            boolean inheritContext = false;
            if (IS_PRE_LOLLIPOP) {
                inheritContext = (attrs instanceof XmlPullParser)
                        // If we have a XmlPullParser, we can detect where we are in the layout
                        ? ((XmlPullParser) attrs).getDepth() > 1
                        // Otherwise we have to use the old heuristic
                        : shouldInheritContext((ViewParent) parent);
            }
    
            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 */
            );
        }
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`mAppCompatViewInflater.createView`方法

final View createView(View parent, final String name, @NonNull Context context, @NonNull AttributeSet attrs, boolean inheritContext, boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
           final Context originalContext = context;
    
           // We can emulate Lollipop's android:theme attribute propagating down the view hierarchy
           // by using the parent's context
           if (inheritContext && parent != null) {
               context = parent.getContext();
           }
           if (readAndroidTheme || readAppTheme) {
               // We then apply the theme on the context, if specified
               context = themifyContext(context, attrs, readAndroidTheme, readAppTheme);
           }
           if (wrapContext) {
               context = TintContextWrapper.wrap(context);
           }
    
           View view = null;
    
           // We need to 'inject' our tint aware Views in place of the standard framework versions
           switch (name) {
               case "TextView":
                   view = createTextView(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "ImageView":
                   view = createImageView(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "Button":
                   view = createButton(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "EditText":
                   view = createEditText(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "Spinner":
                   view = createSpinner(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "ImageButton":
                   view = createImageButton(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "CheckBox":
                   view = createCheckBox(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "RadioButton":
                   view = createRadioButton(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "CheckedTextView":
                   view = createCheckedTextView(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "AutoCompleteTextView":
                   view = createAutoCompleteTextView(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "MultiAutoCompleteTextView":
                   view = createMultiAutoCompleteTextView(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "RatingBar":
                   view = createRatingBar(context, attrs);
                   verifyNotNull(view, name);
                   break;
               case "SeekBar":
                   view = createSeekBar(context, attrs);
                   verifyNotNull(view, name);
                   break;
               default:
                   // The fallback that allows extending class to take over view inflation
                   // for other tags. Note that we don't check that the result is not-null.
                   // That allows the custom inflater path to fall back on the default one
                   // later in this method.
                   view = createView(context, name, attrs);
           }
    
           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 its android:onClick
               checkOnClickListener(view, attrs);
           }
    
           return view;
       }
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这里对创建的View时做了拦截

## 3.总结 ##

> 我们的页面继承普通的`Activity`时没有设置factory,而`AppCompatActivity`设置了factory。所以`AppCompatActivity`中`setContentView`方法加载的系统控件都会被替换

转载于:https://juejin.im/post/5cadeacc6fb9a068b16e09a2

[LayoutInflater_View]: https://juejin.im/post/5cae6cb96fb9a068a84fd2dd