AppCompat兼容性

控件的兼容性 v4 v7 v13 数字代表的是支持的api 的version
AppCompatActivity 是如何做到兼容性的
原理：继承了AppCompatActivity 的Activity 都会在解析XML 的时候，将xml里面所有的系统控件转换为 appCompatButton。它的源码是怎样的呢？所谓的兼容，就是一个着色问题！！！
AppCompatDelegate 的工作就是涂色。替换：widget着色是通过这个widget 的layout 在inflation 的时候，被AppCompatDelegate 拦截下来，然后根据控件的名字，强制被系统转换成为
以AppCompat 开头的控件。

1.首先查看继承的关系

public class AppCompatActivity extends FragmentActivity implements AppCompatCallback,
        TaskStackBuilder.SupportParentable, ActionBarDrawerToggle.DelegateProvider {
public class FragmentActivity extends BaseFragmentActivityJB implements
        ActivityCompat.OnRequestPermissionsResultCallback,
        ActivityCompatApi23.RequestPermissionsRequestCodeValidator {
abstract class BaseFragmentActivityJB extends BaseFragmentActivityHoneycomb {
abstract class BaseFragmentActivityHoneycomb extends BaseFragmentActivityGingerbread {
abstract class BaseFragmentActivityGingerbread extends SupportActivity {
public class SupportActivity extends Activity {

2.AppCompatActivity 中代理的实现

  @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        //获取到代理的实例对象
        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);
    }
     /**
     * @return The {@link AppCompatDelegate} being used by this Activity.
     */
    @NonNull
    public AppCompatDelegate getDelegate() {
        if (mDelegate == null) {
            mDelegate = AppCompatDelegate.create(this, this);
        }
        return mDelegate;
    }
    private static AppCompatDelegate create(Context context, Window window,
            AppCompatCallback callback) {
    //这边会根据不同的系统的版本号得到不同的代理对象，但是其他的本质都是直接，或者间接的继承AppCompatDelegateImplV9的s
        final int sdk = Build.VERSION.SDK_INT;
        if (BuildCompat.isAtLeastN()) {
            return new AppCompatDelegateImplN(context, window, callback);
        } else if (sdk >= 23) {
            return new AppCompatDelegateImplV23(context, window, callback);
        } else if (sdk >= 14) {
            return new AppCompatDelegateImplV14(context, window, callback);
        } else if (sdk >= 11) {
            return new AppCompatDelegateImplV11(context, window, callback);
        } else {
            return new AppCompatDelegateImplV9(context, window, callback);
        }
    }
    //比如AppCompatDelegateImplN  中的继承关系为
    @RequiresApi(24)
    @TargetApi(24)
    class AppCompatDelegateImplN extends AppCompatDelegateImplV23
    @RequiresApi(23)
    @TargetApi(23)
    class AppCompatDelegateImplV23 extends AppCompatDelegateImplV14 
    @RequiresApi(14)
    @TargetApi(14)
    class AppCompatDelegateImplV14 extends AppCompatDelegateImplV11
    @RequiresApi(11)
    @TargetApi(11)
    //当我们在我们的代码中执行了下面的代码的时候
     @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    //执行  setContentView(R.layout.activity_main); 的时候
    @Override
    public void setContentView(@LayoutRes int layoutResID) {
        getDelegate().setContentView(layoutResID);
    }
    //执行getDelegate().setContentView(layoutResID);的时候，就会回调到AppCompatDelegateImplV9中的
    @Override
    public void setContentView(int resId) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        //这边会采用布局加载器来加载布局，这是因为下面为  LayoutInflaterCompat.setFactory(layoutInflater, this);
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }
    class AppCompatDelegateImplV11 extends AppCompatDelegateImplV9
    //AppCompatDelegateImplV9 中部分的代码，这个类为public abstract class AppCompatDelegat中的抽象方法的实现
    @Override
    public void installViewFactory() {
        LayoutInflater layoutInflater = LayoutInflater.from(mContext);
        if (layoutInflater.getFactory() == null) {
            //设置了LayoutInflaterFactory 的回调this
            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");
            }
        }
    }
    //这个方法的回调onCreateView 为public interface LayoutInflaterFactory接口的实现
     /**
     * 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);
    }
    //当执行到createView(parent, name, context, attrs);的时候
    @Override
    public View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs) {
        if (mAppCompatViewInflater == null) {
            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 */
        );
    }
    //当执行到 mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext的时候
    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);
        }
        //name为在布局里面设置的TextView,ImageView,这边就会根据这些名字对应的生成Appcompat对应的控件，这里就是适配的实现，可以在不同的版本下，内容的体现是一样
        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;
    }

LinearLayoutCompat

这个类是干什么的，是控件还是组件，看他的初始化在干什么
找到入口，一般是构造器
找关键方法：onMeasure onLayout onDraw
onMeasure 是计算子控件的大小，同时计算自己的大小。自己的宽高是由子空间的宽高决定的，根据摆放的方向不同而算法不同
onLayout 是将子控件的上下左右位置进行确定。然后布局到layout上面

onDraw 只用来画layout 自己的分割线，其他的内容由具体的item来绘制

@Override
protected void onDraw(Canvas canvas) {
     if (mDivider == null) {
         return;
     }

     if (mOrientation == VERTICAL) {
         drawDividersVertical(canvas);
     } else {
         drawDividersHorizontal(canvas);
     }
 }

void drawDividersVertical(Canvas canvas) {
     final int count = getVirtualChildCount();
     for (int i = 0; i < count; i++) {
         final View child = getVirtualChildAt(i);

         if (child != null && child.getVisibility() != GONE) {
             if (hasDividerBeforeChildAt(i)) {
                 final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                 final int top = child.getTop() - lp.topMargin - mDividerHeight;
                 drawHorizontalDivider(canvas, top);
             }
         }
     }

     if (hasDividerBeforeChildAt(count)) {
         final View child = getVirtualChildAt(count - 1);
         int bottom = 0;
         if (child == null) {
             bottom = getHeight() - getPaddingBottom() - mDividerHeight;
         } else {
             final LayoutParams lp = (LayoutParams) child.getLayoutParams();
             bottom = child.getBottom() + lp.bottomMargin;
         }
         drawHorizontalDivider(canvas, bottom);
     }
 }
 void drawHorizontalDivider(Canvas canvas, int top) {
     mDivider.setBounds(getPaddingLeft() + mDividerPadding, top,
             getWidth() - getPaddingRight() - mDividerPadding, top + mDividerHeight);
     mDivider.draw(canvas);
 }

 void drawVerticalDivider(Canvas canvas, int left) {
     mDivider.setBounds(left, getPaddingTop() + mDividerPadding,
             left + mDividerWidth, getHeight() - getPaddingBottom() - mDividerPadding);
     mDivider.draw(canvas);
 }