LayoutInflater Factory 是什么菩掏？

setFactory(LayoutInflater.Factory factory)
setFactory2(LayoutInflater.Factory2 factory)
setFactory2是在SDK>11時(shí)候添加的刀诬，如果你是基于11以上的就使用setFactory2，否則就使用setFactory ，兩者功能基本一致稍味。當(dāng)然你不想考慮兼容問題可以直接使用LayoutInflaterCompat.setFactory()隧熙。
其實(shí)就是一個(gè)接口，在系統(tǒng)填充view前會(huì)回調(diào)該接口睬魂，你可以去自定義布局的填充（有點(diǎn)類似于攔截器）终吼。

LayoutInflater Factory 有什么用？

使用LayoutInflater Factory的這一特性可以做很多事：

提高view構(gòu)建的效率

當(dāng)我們使用自定義view時(shí)汉买，需要在xml中使用完整類名衔峰，系統(tǒng)實(shí)際就是根據(jù)完整類名進(jìn)行反射構(gòu)建。我們可以自己new出view避免系統(tǒng)反射調(diào)用蛙粘，提高效率垫卤。
替換默認(rèn)view實(shí)現(xiàn)，改變或添加屬性

替換系統(tǒng)控件

一鍵換膚解決方案

LayoutInflater Factory 怎么用出牧？

public class TestLayoutFactory implements LayoutInflaterFactory {

    private static final String TAG = "TestLayoutFactory";

    @Override
    public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        Log.d(TAG, "name = " + name);
        int n = attrs.getAttributeCount();
        for (int i = 0; i < n; i++)
        {
            Log.d(TAG, attrs.getAttributeName(i) + " , " + attrs.getAttributeValue(i));
        }

        return null;
    }

}

@Override
protected void onCreate(Bundle savedInstanceState) {
    // 注意需在調(diào)用super.onCreate(savedInstanceState);之前設(shè)置
    LayoutInflaterCompat.setFactory(getLayoutInflater(), new TestLayoutFactory());
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test_layout_factory);
}

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout  android:id="@+id/activity_test_layout_factory" 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" tools:context="com.example.licheng.testapp.layoutfactory.TestLayoutFactoryActivity">

    <TextView  android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/test" android:textSize="16sp" android:padding="10dp" android:textColor="@android:color/white" android:background="@android:color/black" android:layout_gravity="center"/>

</FrameLayout>

在xml中使用完全類名穴肘。我們看下系統(tǒng)是如何構(gòu)建我們自定義view的，一般的流程：inflate()->createViewFromTag()->CreateView()

我們先看看createViewFromTag()部分重要代碼：

if (view == null) {
    final Object lastContext = mConstructorArgs[0];
    mConstructorArgs[0] = context;
    try {
        if (-1 == name.indexOf('.')) {
            view = onCreateView(parent, name, attrs);
        } else {
            view = createView(name, null, attrs);
        }
    } finally {
        mConstructorArgs[0] = lastContext;
    }
}

這里我們可以看到舔痕，根據(jù)name是否包含“.”來判斷是否是自定義view评抚，如果是自定義view就會(huì)調(diào)用CreateView()

public final View createView(String name, String prefix, AttributeSet attrs)
        throws ClassNotFoundException, InflateException { Constructor<? extends View> constructor = sConstructorMap.get(name); if (constructor != null && !verifyClassLoader(constructor)) { constructor = null; sConstructorMap.remove(name); }
    Class<? extends View> clazz = null;

    try { Trace.traceBegin(Trace.TRACE_TAG_VIEW, name); if (constructor == null) { // Class not found in the cache, see if it's real, and try to add it clazz = mContext.getClassLoader().loadClass( prefix != null ? (prefix + name) : name).asSubclass(View.class); if (mFilter != null && clazz != null) { boolean allowed = mFilter.onLoadClass(clazz); if (!allowed) { failNotAllowed(name, prefix, attrs); }
            }
            constructor = clazz.getConstructor(mConstructorSignature);
            constructor.setAccessible(true);
            sConstructorMap.put(name, constructor);
        } else { // If we have a filter, apply it to cached constructor if (mFilter != null) { // Have we seen this name before? Boolean allowedState = mFilterMap.get(name); if (allowedState == null) { // New class -- remember whether it is allowed clazz = mContext.getClassLoader().loadClass( prefix != null ? (prefix + name) : name).asSubclass(View.class); boolean allowed = clazz != null && mFilter.onLoadClass(clazz); mFilterMap.put(name, allowed); if (!allowed) { failNotAllowed(name, prefix, attrs); }
                } else if (allowedState.equals(Boolean.FALSE)) { failNotAllowed(name, prefix, attrs); }
            }
        }

        Object[] args = mConstructorArgs;
        args[1] = attrs;

        final View view = constructor.newInstance(args);
        if (view instanceof ViewStub) { // Use the same context when inflating ViewStub later. final ViewStub viewStub = (ViewStub) view; viewStub.setLayoutInflater(cloneInContext((Context) args[0])); }
        return view;

    } catch (NoSuchMethodException e) { // 省略代碼... }
}

我們根據(jù)以上代碼可以知道系統(tǒng)根據(jù)標(biāo)簽name反射構(gòu)建我們的自定義view，我們使用LayoutInflater Factory就可以自己去構(gòu)建view :
我們可以不用在xml中寫完整的類名伯复，只要匹配到name我們就可以直接new出自定義view慨代，避免系統(tǒng)反射調(diào)用，提高view創(chuàng)建速度啸如。

替換默認(rèn)View的實(shí)現(xiàn)

@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {

    if (TextUtils.equals("TextView", name)) {
        return new GoTextView(context,attrs);
    }

    return null;
}

其實(shí)兼容包也是這么做的侍匙，我們可以點(diǎn)開support library 的AppCompatActivity

protected void onCreate(@Nullable Bundle savedInstanceState) {
    final AppCompatDelegate delegate = getDelegate();
    delegate.installViewFactory();
    delegate.onCreate(savedInstanceState);
    // 省略代碼....
    super.onCreate(savedInstanceState);
}

AppCompatActivity大部分功能是交給AppCompatDelegate去實(shí)現(xiàn)的，在onCreate中我們可以看到是調(diào)用了installViewFactory()

@Override
public void installViewFactory() {
    LayoutInflater layoutInflater = LayoutInflater.from(mContext);
    if (layoutInflater.getFactory() == null) {
        LayoutInflaterCompat.setFactory(layoutInflater, this);
    } else {
        if (!(LayoutInflaterCompat.getFactory(layoutInflater)
                instanceof AppCompatDelegateImplV9)) {
            Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
                    + " so we can not install AppCompat's");
        }
    }
}

其實(shí)就是設(shè)置了一個(gè)Factory叮雳，我們看下設(shè)置的Factory的具體實(shí)現(xiàn)：

public 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 = 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;
}

從代碼中可以一目了然的看出來想暗，所有繼承AppCompactActivity的Activity中都會(huì)將系統(tǒng)的 xxxView 替換為support library中的 AppCompatxxx妇汗，這就實(shí)現(xiàn)了新增功能與向下兼容。

LayoutInflater Factory 使用中遇到的問題

LayoutInflater Factoty有一個(gè)限制说莫，只能被設(shè)置一次杨箭。如果被多次設(shè)置會(huì)拋出異常

/** * Attach a custom Factory interface for creating views while using * this LayoutInflater. This must not be null, and can only be set once; * after setting, you can not change the factory. * * @see LayoutInflater#setFactory(android.view.LayoutInflater.Factory) */
public static void setFactory(LayoutInflater inflater, LayoutInflaterFactory factory) {
    IMPL.setFactory(inflater, factory);
}

這個(gè)限制就會(huì)導(dǎo)致一個(gè)問題，我們?cè)诶^承AppCompactActivity后設(shè)置自己的Factory會(huì)導(dǎo)致AppCompactActivity的Factory無效储狭，無法使用最新的特性互婿，那該怎么辦的呢？

有以下幾種解決方案：

在Activity的onCreateView()回調(diào)中實(shí)現(xiàn)我們自己的邏輯

使用layoutInflater.cloneInContext(context);克隆一個(gè)layoutInflater晶密，再在這個(gè)克隆的里面setFactory

在我們的Factory中先調(diào)用AppCompatDelegate的createView()在進(jìn)行我們的邏輯

我們來分別介紹一下：

在Activity的onCreateView()回調(diào)中實(shí)現(xiàn)我們自己的邏輯

Activity其實(shí)已經(jīng)實(shí)現(xiàn)了Factory接口擒悬，并把實(shí)現(xiàn)通過接口回調(diào)的方式交給用戶自己去做了，所以我們只需重載onCreateView()

我們看AppCompatDelegate中的代碼稻艰，會(huì)先調(diào)用Activity的OnCreateView懂牧，如果返回不為null則自己進(jìn)行構(gòu)建。

/** * 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
    final View view = callActivityOnCreateView(parent, name, context, attrs);
    if (view != null) {
        return view;
    }

    // If the Factory didn't handle it, let our createView() method try
    return createView(parent, name, context, attrs);
}

所以我們可以在Activity的onCreateView中進(jìn)行“攔截”尊勿，Activity的代碼就是重載onCreateView：

public class TestLayoutFactoryActivity extends AppCompatActivity {

    private static final String TAG = "TestLayoutFactoryActivi";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // 注意需在調(diào)用super.onCreate(savedInstanceState);之前設(shè)置
        //LayoutInflaterCompat.setFactory(getLayoutInflater(), new TestLayoutFactory());
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test_layout_factory);
    }

    @Override
    public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        if (TextUtils.equals("TextView", name)) {
            return new GoTextView(context, attrs);
        }
        // return null 交給系統(tǒng)去構(gòu)建view
        return null;
    }
}

使用layoutInflater.cloneInContext(context);

layoutInflater提供api是cloneInContext(context)僧凤；可以克隆一個(gè)layoutInflater

LayoutInflater newLayoutInlflater = getLayoutInflater().cloneInContext(context);
LayoutInflaterCompat.setFactory(newLayoutInlflater,new TestLayoutFactory());

這種方式不是很方便，需要在使用中將默認(rèn)的LayoutInflater替換為我們新的LayoutInflater元扔，但是也是一種思路躯保。

在Factory中先調(diào)用AppCompatDelegate的createView()

好在AppCompatDelegate的createView()是public的，所以我們可以先執(zhí)行自己的邏輯再交給delegate去實(shí)現(xiàn)：

public class TestLayoutFactory implements LayoutInflaterFactory {

    private AppCompatDelegate appCompatDelegate;

    private static final String TAG = "TestLayoutFactory";

    public TestLayoutFactory(AppCompatDelegate appCompatDelegate) {
        this.appCompatDelegate = appCompatDelegate;
    }

    @Override
    public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        View result = null;

        // 實(shí)現(xiàn)我們自己的邏輯
        if (TextUtils.equals("TextView", name)) {
            result =  new GoTextView(context,attrs);
        }

        if (result == null) {
            // 使用 AppCompat 獲取view
            result = appCompatDelegate.createView(parent, name, context, attrs);
        }
        return result;
    }

LayoutInflater Factory這一特性很強(qiáng)大澎语，能做的遠(yuǎn)不止上面那些事途事。比如大部分“一鍵換膚”都是使用了這一特性來實(shí)現(xiàn)的。