Android LayoutInflater.setFactory2()

前面寫LayoutInflater時看到了LayoutInflater.Factory和LayoutInflater.Factory2接口

在LayoutInflater.createViewFromTag()方法中

        View view;
        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);
        }

調用LayoutInflater.createView()創建View之前會判斷是否有設置Factory/Factory2。若設置，通過Factory/Factory2創建View。當然最終流程還是走的createView()方法反射創建View，只不過在創建之前做了hook處理，下面看看源碼流程。

LayoutInflater

    private Factory mFactory;
    private Factory2 mFactory2;
    private Factory2 mPrivateFactory;

    public void setFactory(Factory factory) {
        if (mFactorySet) {
            throw new IllegalStateException("A factory has already been set on this LayoutInflater");
        }
        if (factory == null) {
            throw new NullPointerException("Given factory can not be null");
        }
        mFactorySet = true;
        if (mFactory == null) {
            mFactory = factory;
        } else {
            mFactory = new FactoryMerger(factory, null, mFactory, mFactory2);
        }
    }

    public void setFactory2(Factory2 factory) {
        //Factory/Factory2只能設置一次，最終都返回的包裝類FactoryMerger
        if (mFactorySet) {
            throw new IllegalStateException("A factory has already been set on this LayoutInflater");
        }
        if (factory == null) {
            throw new NullPointerException("Given factory can not be null");
        }
        mFactorySet = true;
        //設置Factory2也會賦值給Factory
        if (mFactory == null) {
            mFactory = mFactory2 = factory;
        } else {
            mFactory = mFactory2 = new FactoryMerger(factory, factory, mFactory, mFactory2);
        }
    }

    /**
     * @hide for use by framework
     * 官方註釋mPrivateFactory爲framework使用
     */
    public void setPrivateFactory(Factory2 factory) {
        if (mPrivateFactory == null) {
            mPrivateFactory = factory;
        } else {
            mPrivateFactory = new FactoryMerger(factory, factory, mPrivateFactory, mPrivateFactory);
        }
    }

    public interface Factory {
        @Nullable
        View onCreateView(@NonNull String name, @NonNull Context context,
                @NonNull AttributeSet attrs);
    }

    public interface Factory2 extends Factory {
        @Nullable
        View onCreateView(@Nullable View parent, @NonNull String name,
                @NonNull Context context, @NonNull AttributeSet attrs);
    }

    private static class FactoryMerger implements Factory2 {
        private final Factory mF1, mF2;
        private final Factory2 mF12, mF22;

        FactoryMerger(Factory f1, Factory2 f12, Factory f2, Factory2 f22) {
            mF1 = f1;
            mF2 = f2;
            mF12 = f12;
            mF22 = f22;
        }

         //Factory的抽象方法優先調用Factory.onCreateView()
        @Nullable
        public View onCreateView(@NonNull String name, @NonNull Context context,
                @NonNull AttributeSet attrs) {
            View v = mF1.onCreateView(name, context, attrs);
            if (v != null) return v;
            return mF2.onCreateView(name, context, attrs);
        }

         //Factory2的抽象方法優先調用Factory2.onCreateView()
        @Nullable
        public View onCreateView(@Nullable View parent, @NonNull String name,
                @NonNull Context context, @NonNull AttributeSet attrs) {
            View v = mF12 != null ? mF12.onCreateView(parent, name, context, attrs)
                    : mF1.onCreateView(name, context, attrs);
            if (v != null) return v;
            return mF22 != null ? mF22.onCreateView(parent, name, context, attrs)
                    : mF2.onCreateView(name, context, attrs);
        }
    }

其中mPrivateFactory標記爲hide，use by framework。我們可自行設置Factory/Factory2。
下面跟一下setFactory()/setFactory2()方法調用處

LayoutInflaterCompat

    @Deprecated
    public static void setFactory(
            @NonNull LayoutInflater inflater, @NonNull LayoutInflaterFactory factory) {
        if (Build.VERSION.SDK_INT >= 21) {
            inflater.setFactory2(factory != null ? new Factory2Wrapper(factory) : null);
        } else {
            final LayoutInflater.Factory2 factory2 = factory != null
                    ? new Factory2Wrapper(factory) : null;
            inflater.setFactory2(factory2);

            final LayoutInflater.Factory f = inflater.getFactory();
            if (f instanceof LayoutInflater.Factory2) {
                forceSetFactory2(inflater, (LayoutInflater.Factory2) f);
            } else {
                forceSetFactory2(inflater, factory2);
            }
        }
    }

    public static void setFactory2(
            @NonNull LayoutInflater inflater, @NonNull LayoutInflater.Factory2 factory) {
        inflater.setFactory2(factory);

        if (Build.VERSION.SDK_INT < 21) {
            final LayoutInflater.Factory f = inflater.getFactory();
            if (f instanceof LayoutInflater.Factory2) {
                forceSetFactory2(inflater, (LayoutInflater.Factory2) f);
            } else {
                forceSetFactory2(inflater, factory);
            }
        }
    }

筆者sdk版本爲29，setFactory()方法已被標記爲棄用
繼續跟進LayoutInflaterCompat.setFactory2()方法調用處

AppCompatDelegateImpl.installViewFactory()

    @Override
    public void installViewFactory() {
        LayoutInflater layoutInflater = LayoutInflater.from(mContext);
        if (layoutInflater.getFactory() == null) {
            LayoutInflaterCompat.setFactory2(layoutInflater, this);
        } else {
            if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImpl)) {
                Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
                        + " so we can not install AppCompat's");
            }
        }
    }

LayoutInflaterCompat.setFactory2(layoutInflater, this)這裏的this即AppCompatDelegateImpl實現了LayoutInflater.Factory2接口

AppCompatDelegateImpl是AppCompatActivity的代理類

AppCompatActivity.onCreate()

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        final AppCompatDelegate delegate = getDelegate();
        //這裏調用
        delegate.installViewFactory();
        delegate.onCreate(savedInstanceState);
        super.onCreate(savedInstanceState);
    }

也就是說Activity繼承自AppCompatActivity後便爲LayoutInflater設置了Factory2接口，接口實例爲AppCompatDelegateImpl，最終hook操作就在AppCompatDelegateImpl的接口方法中了。

AppCompatDelegateImpl.onCreateView()

    @Override
    public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        return createView(parent, name, context, attrs);
    }

    @Override
    public View onCreateView(String name, Context context, AttributeSet attrs) {
        return onCreateView(null, name, context, attrs);
    }

AppCompatDelegateImpl.CreateView()

   @Override
    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)) {
                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)
                    ? ((XmlPullParser) attrs).getDepth() > 1
                    : 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 */
        );
    }

AppCompatViewInflater.createView()

    final View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs, boolean inheritContext,
            boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
        ...
        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;
            case "ToggleButton":
                view = createToggleButton(context, attrs);
                verifyNotNull(view, name);
                break;
            default:
                view = createView(context, name, attrs);
        }

        if (view == null && originalContext != context) {
            view = createViewFromTag(context, name, attrs);
        }

        if (view != null) {
            checkOnClickListener(view, attrs);
        }

        return view;
    }

    @NonNull
    protected AppCompatTextView createTextView(Context context, AttributeSet attrs) {
        return new AppCompatTextView(context, attrs);
    }

    @NonNull
    protected AppCompatImageView createImageView(Context context, AttributeSet attrs) {
        return new AppCompatImageView(context, attrs);
    }

    @NonNull
    protected AppCompatButton createButton(Context context, AttributeSet attrs) {
        return new AppCompatButton(context, attrs);
    }

    @NonNull
    protected AppCompatEditText createEditText(Context context, AttributeSet attrs) {
        return new AppCompatEditText(context, attrs);
    }
    ...

AppCompatActivity設置的Factory2將系統封裝的常用View變爲同名的AppCompatView以此支持tint屬性。

下面我們自己設置Factory2

class Factory2Activity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        layoutInflater.factory2 = object : LayoutInflater.Factory2 {
            override fun onCreateView(parent: View?, name: String, context: Context, attrs: AttributeSet): View? {
                //調用AppCompatDelegateImpl.CreateView()系統邏輯生成view
                val view = delegate.createView(parent, name, context, attrs)
                if (view != null && view is TextView) {
                    //這裏打印出來是AppCompatTextView
                    Log.d("zjyx", view.javaClass.simpleName)
                    return AppCompatButton(context, attrs)
                }
                return view
            }

            override fun onCreateView(name: String, context: Context, attrs: AttributeSet): View? {
                return null
            }

        }
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_factory)
    }
}

xml只設置了一個TextView

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv_factory"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="text_view"
        android:textColor="@android:color/holo_orange_light"
        android:textSize="20sp" />
</RelativeLayout>

這裏將TextView變爲了AppCompatButton
藉助Factory2接口，可以在BaseActivity中統一對所有View進行處理。包括改變字體，設置view背景色，統一替換等等。

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