Question

我试图制作一个PopupMenu

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    menu_btn.setOnClickListener {
        var menu: PopupMenu?
        menu = PopupMenu(this.context, it)
        menu.inflate(R.menu.card_menu)

        menu.setOnMenuItemClickListener {
            when(it.itemId) {
                R.id.menu_modify -> { Toast.makeText(context, "Modify", Toast.LENGTH_LONG).show()
                    true }

                R.id.menu_delete -> { Toast.makeText(context, "Delete", Toast.LENGTH_LONG).show()
                    true }

                else -> false
            }
        }

        menu.show()
    }
}

但是我在

下出现了模糊的红线

menu = PopupMenu(this.context, it)

说：类型不匹配。需要：语境发现：孔蒂？

甚至当我使用！ -我收到此错误

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
    at com.example.emek1.myapplication.FragmentOne.onCreate(FragmentOne.kt:24)
    at android.support.v4.app.Fragment.performCreate(Fragment.java:2414)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1418)
    at android.support.v4.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1195)
    at android.support.v4.app.FragmentTransition.calculateFragments(FragmentTransition.java:1078)
    at android.support.v4.app.FragmentTransition.startTransitions(FragmentTransition.java:117)
    at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2408)
    at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2366)
    at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:2243)
    at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:654)
    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:146)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1244)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1092)
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1622)

注意：它不在MainActivity.kt中这是一个片段。

Answer 1

NullPointerException源自onCreate()在onCreateView()之前运行，这夸大了视图层次。因此menu_btn仍然为空，因为未找到。再看看Fragments的生命周期。

对于弹出窗口，最好使用Context参数View中的it.context。

Answer 2

编写此代码

context?.let {
    menu = PopupMenu(it, view)
}

这里视图将成为弹出窗口的锚点视图。

代替

menu = PopupMenu(this.context, it)

Answer 3

如果它是片段，则应这样调用上下文。

menu = PopupMenu(activity!!, it)

或者如果您拥有最新的库，则可以执行以下操作

menu = PopupMenu(requireActivity(), it)

Kotlin-类型不匹配：必需：找到上下文：上下文？

3 个答案: