前言
最近的一系列源码分析，都是基于一个错误，逐步深入源码。这样更有目的性的看源码，思路会更清楚一点。
网络上有文章给出了有针对性的解决方案。我通过源码给出更普通的解决思路，这个问题，没有特定的解决方案，所以只能领会精髓后，随机应变。
下面通过我遇到的具体问题，展开源码的分析，所以不必太在意业务场景的相似，重在领会精髓
报错
我的具体场景是，在从某一个界面跳转到登录界面时，点击输入框EditText 时，出现的崩溃。
java.lang.IllegalArgumentException: parameter must be a descendant of this view
at android.view.ViewGroup.offsetRectBetweenParentAndChild(ViewGroup.java:6078)
at android.view.ViewGroup.offsetDescendantRectToMyCoords(ViewGroup.java:6007)
at android.view.FocusFinder.findNextFocusInAbsoluteDirection(FocusFinder.java:365)
at android.view.FocusFinder.findNextFocus(FocusFinder.java:268)
at android.view.FocusFinder.findNextFocus(FocusFinder.java:110)
at android.view.FocusFinder.findNextFocus(FocusFinder.java:80)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1027)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.ViewGroup.focusSearch(ViewGroup.java:1029)
at android.view.View.focusSearch(View.java:10843)
at android.widget.TextView.onCreateInputConnection(TextView.java:7862)
at androidx.appcompat.widget.AppCompatEditText.onCreateInputConnection(AppCompatEditText.java:186)
at android.view.inputmethod.InputMethodManager.startInputInner(InputMethodManager.java:1290)
at android.view.inputmethod.InputMethodManager.checkFocus(InputMethodManager.java:1485)
at android.view.inputmethod.InputMethodManager.viewClicked(InputMethodManager.java:1667)
at android.widget.TextView.viewClicked(TextView.java:12009)
at android.widget.TextView.onTouchEvent(TextView.java:10109)
at android.view.View.dispatchTouchEvent(View.java:12513)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:3030)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2719)
at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:440)
at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1830)
at android.app.Activity.dispatchTouchEvent(Activity.java:3400)
源码分析 Android 获取View焦点的流程
深入剖析崩溃的原因，涉及到Android其他方面的知识，所以这里只分析到引出这个异常的地方
下面是跳转到登录界面后，点击输入框EditText 时，点击事件层层分发，到focusSearch 在指定方向上，搜索下一个可以获取焦点的View
在这里插入图片描述
mParent.focusSearch(this, direction)有两处实现，分别是：RecyclerView 、ViewGroup
下面分析ViewGroup中的focusSearch(this, direction)
代码段1
/**
* Find the nearest view in the specified direction that wants to take
* focus.
*
* @param focused The view that currently has focus
* @param direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and
* FOCUS_RIGHT, or 0 for not applicable.
*/
@Override
public View focusSearch(View focused, int direction) {
if (isRootNamespace()) {
//如果是根布局也就是 DecorView
// root namespace means we should consider ourselves the top of the
// tree for focus searching; otherwise we could be focus searching
// into other tabs. see LocalActivityManager and TabHost for more info.
return FocusFinder.getInstance().findNextFocus(this, focused, direction);
} else if (mParent != null) {
//不断调用父视图的focusSearch
return mParent.focusSearch(focused, direction);
}
return null;
}
接着调用了FocusFinder 里面的函数 findNextFocus(ViewGroup root, View focused, int direction)
代码段2
/**
* Find the next view to take focus in root's descendants, starting from the view
* that currently is focused.
* @param root Contains focused. Cannot be null.
* @param focused Has focus now.
* @param direction Direction to look.
* @return The next focusable view, or null if none exists.
*/
public final View findNextFocus(ViewGroup root, View focused, int direction) {
return findNextFocus(root, focused, null, direction);
}
代码段3
private View findNextFocus(ViewGroup root, View focused, Rect focusedRect, int direction) {
View next = null;
ViewGroup effectiveRoot = getEffectiveRoot(root, focused);
if (focused != null) {
//查找下一个由用户指定的可获取焦点的View
//那么如何指定下一个获取焦点的view呢？通过View 中的一系列函数 setNextFocusLeftId setNextFocusRightId setNextFocusUpId setNextFocusDownId setNextFocusForwardId 来设置
next = findNextUserSpecifiedFocus(effectiveRoot, focused, direction);
}
if (next != null) {
//如果找到符合条件的view，则返回
return next;
}
// 如果没有找到，则通过遍历root（也就是DecorView）下所有的可获取焦点的非touch_mode的 view
ArrayList focusables = mTempList;
try {
focusables.clear();
//遍历是从这个函数开始的，所有符合条件的view被添加到focusables
effectiveRoot.addFocusables(focusables, direction);
if (!focusables.isEmpty()) {
//在focusables 中查询，下一个可以获取焦点的view
next = findNextFocus(effectiveRoot, focused, focusedRect, direction, focusables);
}
} finally {
focusables.clear();
}
return next;
}
下面详细的分析一下 effectiveRoot.addFocusables(focusables, direction);：
代码段4
/**
* Add any focusable views that are descendants of this view (possibly
* including this view if it is focusable itself) to views. If we are in touch mode,
* only add views that are also focusable in touch mode.
*
* @param views Focusable views found so far
* @param direction The direction of the focus
*/
public void addFocusables(ArrayList views, @FocusDirection int direction) {
//这个方法有5个地方实现了它：DrawerLayout、RecyclerView、View、ViewGroup、ViewPage
addFocusables(views, direction, isInTouchMode() ? FOCUSABLES_TOUCH_MODE : FOCUSABLES_ALL);
}
下面主要对ViewGroup和View 中的addFocusables 进行分析
View 中的addFocusables 函数
代码段5
public void addFocusables(ArrayList views, @FocusDirection int direction,
@FocusableMode int focusableMode) {
if (views == null) {
return;
}
//如果不能获取焦点，就不添加到views中，直接返回
if (!canTakeFocus()) {
return;
}
//如果是触摸模式，并且在触摸模式下不能获取焦点，直接返回
//也就是说，如果不是触摸模式或者触摸模式下可获取焦点，就添加到views
if ((focusableMode & FOCUSABLES_TOUCH_MODE) == FOCUSABLES_TOUCH_MODE
&& !isFocusableInTouchMode()) {
return;
}
views.add(this);
}
关于TOUCH_MODE更详细的说明，参考官方博客
ViewGroup 中的addFocusables 函数
代码段6
@Override
public void addFocusables(ArrayList views, int direction, int focusableMode) {
final int focusableCount = views.size();
//自身ViewGroup与它后代view的关系，是在后代view之前、之后获取焦点，或者不让后台view 获取焦点
final int descendantFocusability = getDescendantFocusability();
final boolean blockFocusForTouchscreen = shouldBlockFocusForTouchscreen();
//isFocusableInTouchMode() 在touchMode下 是否可以获取或保持焦点
final boolean focusSelf = (isFocusableInTouchMode() || !blockFocusForTouchscreen);
//后代view不能获取焦点
if (descendantFocusability == FOCUS_BLOCK_DESCENDANTS) {
//自己可以获取焦点
if (focusSelf) {
//调用view 中的addFocusables，把当前布局添加到views
super.addFocusables(views, direction, focusableMode);
}
return;
}
if (blockFocusForTouchscreen) {
focusableMode |= FOCUSABLES_TOUCH_MODE;
}
//在后代view之前获取焦点，并且自己可以获取焦点
if ((descendantFocusability == FOCUS_BEFORE_DESCENDANTS) && focusSelf) {
//调用view 中的addFocusables，把当前布局添加到views
super.addFocusables(views, direction, focusableMode);
}
int count = 0;
final View[] children = new View[mChildrenCount];
for (int i = 0; i < mChildrenCount; ++i) {
View child = mChildren[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE) {
//获取当前view 下可见的子view
children[count++] = child;
}
}
FocusFinder.sort(children, 0, count, this, isLayoutRtl());
for (int i = 0; i < count; ++i) {
//遍历子view，如果是view就添加到 views，如果是viewGroup就再次调用addFocusables进行判断
children[i].addFocusables(views, direction, focusableMode);
}
// When set to FOCUS_AFTER_DESCENDANTS, we only add ourselves if
// there aren't any focusable descendants. this is
// to avoid the focus search finding layouts when a more precise search
// among the focusable children would be more interesting.
//在后代view之后获取焦点，并且自己可以获取焦点 并且仅在没有可聚焦后代（views的数量没有变）的情况下添加自己
if ((descendantFocusability == FOCUS_AFTER_DESCENDANTS) && focusSelf
&& focusableCount == views.size()) {
super.addFocusables(views, direction, focusableMode);
}
}
这篇文章所给出的解决方法，就是
代码段3 中effectiveRoot.addFocusables(focusables, direction);调用后 ，focusables 中是所有可获取焦点的View，在非空的情况下调用如下代码findNextFocus函数
代码段7
private View findNextFocus(ViewGroup root, View focused, Rect focusedRect,
int direction, ArrayList focusables) {
if (focused != null) {
//本篇文章分析的流程，focused 不为空
if (focusedRect == null) {
focusedRect = mFocusedRect;
}
// fill in interesting rect from focused
//获取focused所在的矩形区域到mOtherRect中
focused.getFocusedRect(focusedRect);
//把focused的坐标，转换为相对于root的坐标
root.offsetDescendantRectToMyCoords(focused, focusedRect);
} else {
//如果focused 为空，就在root布局的指定方向添加一个focusedRect
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);
}
}
- 如果focused不是null，说明当前获取到焦点的View存在，则获得绘制焦点的Rect到focusedRect，然后根据rootView遍历所有ParentView从子View纠正坐标到根View坐标。
- 如果focused是null，则说明当前没有View获取到焦点，则把focusedRect根据不同的direction重置为“一点”。
根据direction调用FocusFinder::findNextFocusInAbsoluteDirection方法进行对比查找“下一个”View。
代码段8
View findNextFocusInAbsoluteDirection(ArrayList focusables, ViewGroup root, View focused,
Rect focusedRect, int direction) {
// initialize the best candidate to something impossible
// (so the first plausible view will become the best choice)
//先设置focusedRect 为最佳的候选矩阵
mBestCandidateRect.set(focusedRect);
//根据不同的方向，偏移一个像素，为了方便比较？
switch(direction) {
case View.FOCUS_LEFT:
mBestCandidateRect.offset(focusedRect.width() + 1, 0);
break;
case View.FOCUS_RIGHT:
mBestCandidateRect.offset(-(focusedRect.width() + 1), 0);
break;
case View.FOCUS_UP:
mBestCandidateRect.offset(0, focusedRect.height() + 1);
break;
case View.FOCUS_DOWN:
mBestCandidateRect.offset(0, -(focusedRect.height() + 1));
}
View closest = null;
int numFocusables = focusables.size();
for (int i = 0; i < numFocusables; i++) {
View focusable = focusables.get(i);
// only interested in other non-root views
if (focusable == focused || focusable == root) continue;
// get focus bounds of other view in same coordinate system
//获取focusable所在的矩形区域到mOtherRect中，这个focusable是之前获取的可聚焦的views
focusable.getFocusedRect(mOtherRect);
//把focusable的坐标（矩阵），转换为相对于root的坐标（矩阵）
root.offsetDescendantRectToMyCoords(focusable, mOtherRect);
//mOtherRect 是否比mBestCandidateRect 更优
if (isBetterCandidate(direction, focusedRect, mOtherRect, mBestCandidateRect)) {
//如果mOtherRect 更优，则mBestCandidateRect设置为mOtherRect ，for循环结束后，得到最优的
mBestCandidateRect.set(mOtherRect);
closest = focusable;
}
}
//返回最优的view
return closest;
}
代码段9
/**
* Offset a rectangle that is in a descendant's coordinate
* space into our coordinate space.
* @param descendant A descendant of this view
* @param rect A rectangle defined in descendant's coordinate space.
*/
public final void offsetDescendantRectToMyCoords(View descendant, Rect rect) {
offsetRectBetweenParentAndChild(descendant, rect, true, false);
}
代码段10
/**
* Helper method that offsets a rect either from parent to descendant or
* descendant to parent.
*/
void offsetRectBetweenParentAndChild(View descendant, Rect rect,
boolean offsetFromChildToParent, boolean clipToBounds) {
// already in the same coord system :)
if (descendant == this) {
return;
}
ViewParent theParent = descendant.mParent;
// search and offset up to the parent
//通过不断的循环，把descendant的坐标，也就是矩阵rect，转换为相对于当前view（因为offsetRectBetweenParentAndChild是view的方法）的坐标（矩阵）
while ((theParent != null)
&& (theParent instanceof View)
&& (theParent != this)) {
if (offsetFromChildToParent) {
//偏移矩阵，例如：布局viewGoupA 里面有viewGoupB 里面有 view C
//把view C 相对于父布局viewGoupB的坐标转换为相对于viewGoupA的坐标
//这里mLeft 相对于父布局的x坐标，-x方向滚动的距离mScrollX，才是原来真是的位置
rect.offset(descendant.mLeft - descendant.mScrollX,
descendant.mTop - descendant.mScrollY);
if (clipToBounds) {
//修剪矩阵
View p = (View) theParent;
//intersect 压紧到公共区域
boolean intersected = rect.intersect(0, 0, p.mRight - p.mLeft,
p.mBottom - p.mTop);
if (!intersected) {
rect.setEmpty();
}
}
} else {
//上面的反向操作，布局viewGoupA 里面有viewGoupB 里面有 view C
//view C 已经转为相对viewGoupA的坐标了，下面的操作就是转为相对于viewGoupB的坐标
if (clipToBounds) {
View p = (View) theParent;
boolean intersected = rect.intersect(0, 0, p.mRight - p.mLeft,
p.mBottom - p.mTop);
if (!intersected) {
rect.setEmpty();
}
}
//偏移矩阵，从父view 到子view
rect.offset(descendant.mScrollX - descendant.mLeft,
descendant.mScrollY - descendant.mTop);
}
descendant = (View) theParent;
theParent = descendant.mParent;
}
// now that we are up to this view, need to offset one more time
// to get into our coordinate space
if (theParent == this) {
if (offsetFromChildToParent) {
rect.offset(descendant.mLeft - descendant.mScrollX,
descendant.mTop - descendant.mScrollY);
} else {
rect.offset(descendant.mScrollX - descendant.mLeft,
descendant.mScrollY - descendant.mTop);
}
} else {
//经过我的分析，这个错误只有两种情况
throw new IllegalArgumentException("parameter must be a descendant of this view");
}
}
经过我的分析，这个错误只有两种情况:
- descendant 不是当前view 的后代 ,(theParent instanceof View) == false 退出循环 ，descendant 为ViewRootImpl （就是这个解决方法[Another java.lang.IllegalArgumentException: parameter must be a descendant of this view](https://stackoverflow.com/questions/30585561/another-java-lang-illegalargumentexception-parameter-must -be-a-descendant-of-th)）
-
descendant 的mParent为空 (theParent != null) == false 退出循环。我遇到的就是这个问题
在这里插入图片描述
下面继续回到代码段8，来看看函数isBetterCandidate是怎么比较出更优的rect
代码段11
/**
* Is rect1 a better candidate than rect2 for a focus search in a particular
* direction from a source rect? This is the core routine that determines
* the order of focus searching.
* @param direction the direction (up, down, left, right)
* @param source The source we are searching from
* @param rect1 The candidate rectangle
* @param rect2 The current best candidate.
* @return Whether the candidate is the new best.
*/
boolean isBetterCandidate(int direction, Rect source, Rect rect1, Rect rect2) {
// to be a better candidate, need to at least be a candidate in the first
// place :)
//rect1是否在source的指定方向direction的下一个可获得焦点的矩阵
if (!isCandidate(source, rect1, direction)) {
//rect1不是候选的，说明rect1 没有rect2 更优，返回false
return false;
}
// we know that rect1 is a candidate.. if rect2 is not a candidate,
// rect1 is better
if (!isCandidate(source, rect2, direction)) {
//rect2不是候选的，说明rect1 比rect2 更优，返回true
return true;
}
//如果都是候选的，比较rect1 和rect2 哪个更优，比较的方法大概是：两个候选rect分表与source比较，是否重叠，是否在希望的方向上等
// if rect1 is better by beam, it wins
if (beamBeats(direction, source, rect1, rect2)) {
return true;
}
// if rect2 is better, then rect1 cant' be :)
if (beamBeats(direction, source, rect2, rect1)) {
return false;
}
// otherwise, do fudge-tastic comparison of the major and minor axis
return (getWeightedDistanceFor(
majorAxisDistance(direction, source, rect1),
minorAxisDistance(direction, source, rect1))
< getWeightedDistanceFor(
majorAxisDistance(direction, source, rect2),
minorAxisDistance(direction, source, rect2)));
}
解决方法：
根据上面的原因，对应两种解决方法：
1、就是可获取焦点的view是在报错View的后代
2、保证可获取焦点view的mParent 不为null
这篇文章，与我分析的第二种解决方案一样，他给出的解决方案更为具体，可以参考
【原创】【ViewFlow+GridView】Parameter must be a descendant of this view问题分析
这篇文章，分析了本篇文章中，未涉及到的其他的几处代码实现
Android焦点流程代码分析