parameter must be a descendant of this view 报错解决方案及Android 获取View焦点源码分析
Posted 薛瑄
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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
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<View> 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<View> 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<View> 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<View> 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<View> 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<View> 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以上是关于parameter must be a descendant of this view 报错解决方案及Android 获取View焦点源码分析的主要内容，如果未能解决你的问题，请参考以下文章
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