已使用 FragmentPagerAdapter 添加的片段答案

【问题标题】：Fragment already added with FragmentPagerAdapter已使用 FragmentPagerAdapter 添加的片段
【发布时间】：2018-01-29 13:09:40
【问题描述】：

我有一个带有 ViewPager 的 Activity，这个 ViewPager 包含 3 个片段。

我正在使用 FragmentPagerAdapter 创建片段，如下所示：

    class ViewPagerUser(fragmentManager: FragmentManager, private val matchDetails: MatchDetails, private val context: Context) : FragmentPagerAdapter(fragmentManager) {

    // Returns total number of pages
    override fun getCount(): Int {
        return NUM_ITEMS
    }

    // Returns the fragment to display for that page
    override fun getItem(position: Int): Fragment? {
        when (position) {
            0 -> return FragmentDetailMatchInfoUser.newInstance(matchDetails)
            1 -> return FragmentDetailMatchParticipantsUser.newInstance(matchDetails)
            2 -> return FragmentDetailMatchWall.newInstance(matchDetails)
            else -> return null
        }
    }

    // Returns the page title for the top indicator
    override fun getPageTitle(position: Int): CharSequence? {
        when (position) {
            0 -> return context.getString(R.string.info)
            1 -> return context.getString(R.string.player)
            2 -> return context.getString(R.string.wall)
            else -> return null
        }
    }

    companion object {
        private val NUM_ITEMS = 3
    }
}

我就是这样用的

    if (matchDetails != null && (matchDetails.cancelled!! || screenType == App.USER || matchDetails.matchStatus == 40 || matchDetails.matchStatus == 50)) {
        adapterViewPager = ViewPagerUser(supportFragmentManager, matchDetails, this)
    } else if (screenType == App.ORGANIZER) {
        adapterViewPager = ViewPagerOrganizer(supportFragmentManager, matchDetails!!, this)
    }

    viewPager?.adapter = adapterViewPager

    viewPager?.offscreenPageLimit = 3

我认为这是在 ViewPager 中处理 Fragment 的最佳方式，但我收到许多关于“已添加 Fragment”的 Crashlytics 报告，如下面的日志所示：

Fatal Exception: java.lang.IllegalStateException: Fragment already added: FragmentDetailMatchInfoUser{b17d64 #0 id=0x7f090551 android:switcher:2131297617:0}
   at android.support.v4.app.FragmentManagerImpl.addFragment(Unknown Source)
   at android.support.v4.app.BackStackRecord.addOp(Unknown Source)
   at android.support.v4.app.FragmentManagerImpl.executeOps(Unknown Source)
   at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(Unknown Source)
   at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(Unknown Source)
   at android.support.v4.app.FragmentManagerImpl.execSingleAction(Unknown Source)
   at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(Unknown Source)
   at android.support.v4.app.FragmentPagerAdapter.finishUpdate(Unknown Source)
   at android.support.v4.view.ViewPager.initViewPager(Unknown Source)
   at android.support.v4.view.ViewPager.populate(Unknown Source)
   at android.support.v4.view.ViewPager.onMeasure(Unknown Source)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
   at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
   at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.support.design.widget.CoordinatorLayout.onMeasureChild(Unknown Source)
   at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(Unknown Source)
   at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(Unknown Source)
   at android.support.design.widget.CoordinatorLayout.onMeasure(Unknown Source)
   at android.view.View.measure(View.java:19883)
   at android.support.constraint.ConstraintLayout.internalMeasureChildren(Unknown Source)
   at android.support.constraint.ConstraintLayout.onMeasure(Unknown Source)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
   at android.support.v7.widget.ContentFrameLayout.onMeasure(Unknown Source)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
   at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
   at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
   at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
   at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6087)
   at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
   at com.android.internal.policy.DecorView.onMeasure(DecorView.java:689)
   at android.view.View.measure(View.java:19883)
   at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2293)
   at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1384)
   at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1637)
   at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1272)
   at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6408)
   at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
   at android.view.Choreographer.doCallbacks(Choreographer.java:686)
   at android.view.Choreographer.doFrame(Choreographer.java:621)
   at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
   at android.os.Handler.handleCallback(Handler.java:751)
   at android.os.Handler.dispatchMessage(Handler.java:95)
   at android.os.Looper.loop(Looper.java:154)
   at android.app.ActivityThread.main(ActivityThread.java:6165)
   at java.lang.reflect.Method.invoke(Method.java)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)

我在 Stackoverflow 中解决了与此问题相关的几乎所有问题，但建议的答案对我无济于事......错误总是会回来。

是不是我做错了什么？

【问题讨论】：

通过此错误表示，您正在尝试添加已经在堆栈中的片段。您是否尝试在 viewpager 之外添加片段？
不，我没有明确调用 addFragment。
尝试在出错的地方添加if(yourFragment.isAdded()){ return; }。
你可以使用viewpager2来解决这个问题see the approach

标签： android android-fragments android-viewpager fragment

【解决方案1】：

此报告可能是因为您在每次 ViewPager 请求片段时都在创建片段的新实例。

您应该在创建 ViewPager 时尝试创建片段实例：

class ViewPagerUser(fragmentManager: FragmentManager, private val matchDetails: MatchDetails, private val context: Context) : FragmentPagerAdapter(fragmentManager) {

private val fragmentDetailMatchInfoUser = FragmentDetailMatchInfoUser.newInstance(matchDetails)
private val fragmentDetailMatchParticipantsUser = FragmentDetailMatchParticipantsUser.newInstance(matchDetails)
private val fragmentDetailMatchWall = FragmentDetailMatchWall.newInstance(matchDetails)

    // Returns total number of page
    override fun getCount(): Int {
        return NUM_ITEMS
    }

    // Returns the fragment to display for that page
    override fun getItem(position: Int): Fragment? {
        when (position) {
            0 -> return fragmentDetailMatchInfoUser
            1 -> return fragmentDetailMatchParticipantsUser
            2 -> return fragmentDetailMatchWall
            else -> return null
        }
    }

    // Returns the page title for the top indicator
    override fun getPageTitle(position: Int): CharSequence? {
        when (position) {
            0 -> return context.getString(R.string.info)
            1 -> return context.getString(R.string.player)
            2 -> return context.getString(R.string.wall)
            else -> return null
        }
    }

    companion object {
        private val NUM_ITEMS = 3
    }
 }

我有类似的问题，它帮助了我。希望对你也有帮助。

【讨论】：

试过了，已发送到生产环境，但 Crashlytics 中再次显示错误 =(
你确定这是你解决问题的唯一方法吗？
这段代码与问题中的代码有何不同？
@Mitch 此代码在创建 ViewPagerAdapter 时初始化页面片段。其他代码每次调用getItem时都会初始化页面片段，从而每次都初始化一个新的片段。

【解决方案2】：

使用isAdded() 检查片段是否与活动分离。

if (!mFragmentDetailMatchInfoUser.isAdded()) {
    return FragmentDetailMatchInfoUser.newInstance(matchDetails);
}

还有两个片段。

【讨论】：

我应该把你的答案和安德烈的答案结合起来吗？（下面的答案）
我不这么认为。如果碎片太多怎么办？这不是最佳做法。而且，他的回答与您的问题无关。您的问题是您正在尝试附上已经添加的片段。您只需要在添加之前检查。所以我认为足以解决您的问题。
但是，如果你看到我的开场问题，我正在使用 FragmentPagerAdapter，我没有片段的引用......每次被问到我都会返回一个新的。在您的回答中，您告诉我检查是否未添加片段的引用（建议由安德烈的回答创建），我错了吗？
如果我这样做会浪费内存？
考虑到这个问题，这不是一个相关的答案！如果问题与FragmentPagerAdapter 的ViewPager 无关，这将是一个答案

【解决方案3】：

我遇到了同样的问题，我通过向 FragmentPagerAdapter 添加第二个参数得到解决，如下所示：

类 ViewPagerUser(fragmentManager: FragmentManager, private val matchDetails: MatchDetails, private val context: Context) : FragmentPagerAdapter(fragmentManager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {...}

更多： FragmentPagerAdapter(fragmentManager) 已弃用，您必须更改为 FragmentPagerAdapter(fragmentManager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) 才能解决问题。

【讨论】：