Android焦点分发基础

本文转载自：http://www.cnblogs.com/myzh/p/3664544.html?utm_source=tuicool&utm_medium=referral 请尊重原创

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