理解焦点处理原理的相关记录

焦点处理相关记录

以下所涉及的焦点部分，只是按键移动部分，不明确包含Touch Focus部分

需解决问题

控件的下一个焦点是哪？

分析思路

当用户通过按键（遥控器等）触发焦点切换时，事件指令会通过底层进行一系列处理。 在ViewRootImpl.java中有一个方法,deliverKeyEventPostIme(...),因为涉及到底层代码，所以没有详细的跟踪分析此方法的调用逻辑,根据网上的资料,按键相关的处理会经过此方法。

private void deliverKeyEventPostIme(QueuedInputEvent q) {
    ...
    // Handle automatic focus changes.
    if (event.getAction() == KeyEvent.ACTION_DOWN) {
      int direction = 0;
      switch (event.getKeyCode()) {
        case KeyEvent.KEYCODE_DPAD_LEFT:
          if (event.hasNoModifiers()) {
            direction = View.FOCUS_LEFT;
          }
          break;
        case KeyEvent.KEYCODE_DPAD_RIGHT:
          if (event.hasNoModifiers()) {
            direction = View.FOCUS_RIGHT;
          }
          break;
        ...
      }
      if (direction != 0) {
        View focused = mView.findFocus();
        if (focused != null) {
          View v = focused.focusSearch(direction);
          if (v != null && v != focused) {
             .....
            if (v.requestFocus(direction, mTempRect)) {
              ...finishInputEvent(q, true);
              return;
            }
          }
          ...
        }
      }

由此方法可以看出，最主要的两个核心过程：

View v = focused.focusSearch(direction);
    v.requestFocus(direction, mTempRect)

接下来详细的分析下，看看过程中进行了什么操作

具体分析

在具体分析前,首先我们先明确下相关变量的定义

View mView : 主体View[DecorView]

//一般把主View“DecorView”添加到WindowManagerImpl中(通过addView)
    //WindowManagerImpl.java
      private void addView(View view...) {
        ViewRootImpl root;
        root = new ViewRootImpl(view.getContext());
        ...
        root.setView(view, wparams, panelParentView);
        ...
      }

    //ViewRootImpl.java
    public void setView(View view....) {
      synchronized (this) {
        if (mView == null) {
          mView = view;
          ...
        }
      ...
      }
    }

所以mView是一个DecorView类型的变量.

View focused :

View focused = mView.findFocus();

    //PhoneWindow.java
    private final class DecorView extends FrameLayout implements RootVie.... {
      ...
    }

    //FrameLayout.java
    public class FrameLayout extends ViewGroup {
      ...
    }

    //ViewGroup.java
    //mFocused记录的是当前被焦点选中的view
    @Override
    public View findFocus() {
    if (DBG) {
      System.out.println("Find focus in " + this + ": flags="
          + isFocused() + ", child=" + mFocused);
    }
    if (isFocused()) {
      return this;
    }
    if (mFocused != null) {
      return mFocused.findFocus();
    }
    return null;
  }

所以最终得到的focused为当前页面中得到焦点的view.

在明确的相关变量后,我们开始View v = focused.focusSearch(direction)的具体分析.

//View.java
   public View focusSearch(int direction) {
   //如果存在父控件,则执行父控件的focusSearch方法
    if (mParent != null) {
      return mParent.focusSearch(this, direction);
    } else {
      return null;
    }
  }
  //ViewGroup.java
  public View focusSearch(View focused, int direction) {
    //判断是否为顶层布局,若是则执行对应方法,若不是则继续向上寻找,说明会从内到外的一层层进行判断，直到最外层的布局为止
    if (isRootNamespace()) {
      return FocusFinder.getInstance().findNextFocus(this, focused, direction);
    } else if (mParent != null) {
      return mParent.focusSearch(focused, direction);
    }
    return null;
  }

说明在这个过程中,其实是从里层开始一直遍历到最外层布局，然后在最外层布局将处理交给了FocusFinder中的方法.

FocusFinder.getInstance().findNextFocus(this, focused, direction);

那我们来看看此方法具体做了什么操作

//FocusFinder.java
    public final View findNextFocus(ViewGroup root, View focused, int direction) {
        return findNextFocus(root, focused, null, direction);
    }

//FocusFinder.java
  private View findNextFocus(ViewGroup root, View focused, Rect focusedRect, int direction) {
    View next = null;
    if (focused != null) {
      next = findNextUserSpecifiedFocus(root, focused, direction);
    }
    if (next != null) {
      return next;
    }
    ArrayList<View> focusables = mTempList;
    try {
      focusables.clear();
      root.addFocusables(focusables, direction);
      if (!focusables.isEmpty()) {
        next = findNextFocus(root, focused, focusedRect, direction, focusables);
      }
    } finally {
      focusables.clear();
    }
    return next;
  }

发现在findNextFocus的执行过程的开始，先执行了findNextUserSpecifiedFocus(...)方法,由代码可以看出，此方法先去判断特定Id值是否存在,若存在则查询出Id对应的view.其实这些Id就是xml里通过android:nextFocusUp="..."等或者代码特别指定的焦点顺序.所以在此过程先判断，若存在,说明下个焦点已经找到,直接返回.

//FocusFinder.java
  private View findNextUserSpecifiedFocus(ViewGroup root, View focused, int direction) {
    // check for user specified next focus
    View userSetNextFocus = focused.findUserSetNextFocus(root, direction);
    if (userSetNextFocus != null && userSetNextFocus.isFocusable()
        && (!userSetNextFocus.isInTouchMode()
            || userSetNextFocus.isFocusableInTouchMode())) {
      return userSetNextFocus;
    }
    return null;
  }

  //View.java
  View findUserSetNextFocus(View root, int direction) {
    switch (direction) {
      case FOCUS_LEFT:
        if (mNextFocusLeftId == View.NO_ID) return null;
        return findViewInsideOutShouldExist(root, mNextFocusLeftId);
      case FOCUS_RIGHT:
        if (mNextFocusRightId == View.NO_ID) return null;
        return findViewInsideOutShouldExist(root, mNextFocusRightId);
      case FOCUS_UP:
        if (mNextFocusUpId == View.NO_ID) return null;
        return findViewInsideOutShouldExist(root, mNextFocusUpId);
      case FOCUS_DOWN:
        if (mNextFocusDownId == View.NO_ID) return null;
        return findViewInsideOutShouldExist(root, mNextFocusDownId);
      case FOCUS_FORWARD:
        if (mNextFocusForwardId == View.NO_ID) return null;
        return findViewInsideOutShouldExist(root, mNextFocusForwardId);
      case FOCUS_BACKWARD: {
        if (mID == View.NO_ID) return null;
        final int id = mID;
        return root.findViewByPredicateInsideOut(this, new Predicate<View>() {
          @Override
          public boolean apply(View t) {
            return t.mNextFocusForwardId == id;
          }
        });
      }
    }
    return null;
  }

如果上面过程没有查询到，则会执行到findNextFocus(...)方法.在这个方法中，先通过offsetDescendantRectToMyCoords(...)方法获得焦点控件的位置矩阵.然后通过比较得到下一个焦点的控件。具体的比较规则可以查看findNextFocusInRelativeDirection(...)方法与findNextFocusInAbsoluteDirection(...)方法.

//FocusFinder.java
  private View findNextFocus(ViewGroup root, View focused, Rect focusedRect,
      int direction, ArrayList<View> focusables) {
    if (focused != null) {
      if (focusedRect == null) {
        focusedRect = mFocusedRect;
      }
      // fill in interesting rect from focused
      focused.getFocusedRect(focusedRect);
      root.offsetDescendantRectToMyCoords(focused, focusedRect);
    } else {
      if (focusedRect == null) {
        focusedRect = mFocusedRect;
        // make up a rect at top left or bottom right of root
        switch (direction) {
          case View.FOCUS_RIGHT:
          case View.FOCUS_DOWN:
            setFocusTopLeft(root, focusedRect);
            break;
          case View.FOCUS_FORWARD:
            if (root.isLayoutRtl()) {
              setFocusBottomRight(root, focusedRect);
            } else {
              setFocusTopLeft(root, focusedRect);
            }
            break;
          case View.FOCUS_LEFT:
          case View.FOCUS_UP:
            setFocusBottomRight(root, focusedRect);
            break;
          case View.FOCUS_BACKWARD:
            if (root.isLayoutRtl()) {
              setFocusTopLeft(root, focusedRect);
            } else {
              setFocusBottomRight(root, focusedRect);
            break;
          }
        }
      }
    }
    switch (direction) {
      case View.FOCUS_FORWARD:
      case View.FOCUS_BACKWARD:
        return findNextFocusInRelativeDirection(focusables, root, focused, focusedRect,
            direction);
      case View.FOCUS_UP:
      case View.FOCUS_DOWN:
      case View.FOCUS_LEFT:
      case View.FOCUS_RIGHT:
        return findNextFocusInAbsoluteDirection(focusables, root, focused,
            focusedRect, direction);
      default:
        throw new IllegalArgumentException("Unknown direction: " + direction);
    }
  }

结论

查找焦点的过程，主要是从View的focusSearch(...)方法开始,从当前焦点开始逐层往外,最终在最外层布局执行FocusFinder中的核心方法来获得下个焦点所在的视图view.

如果需要指定跳转，可以在逐层focusSearch(...)的时候，返回特定的view

转载：http://www.tuicool.com/articles/EjiYRz