未附加 AlertDialog 侦听器

Question

MyAlertDialog 在尝试将上下文设置为侦听器时抛出 ClassCastException。我正在从片段调用 MyAlertDailog。

我正在使用 android 开发文档中的指南。

https://developer.android.com/guide/topics/ui/dialogs#PassingEvents

我的片段

class MyFragment : Fragment(), MyAlerDialog.MyAlertDialogListener {

    ...

    fun launchAlertDialog() {
        val dailog = MyAlertDialog().also {
            it.show(requireActivity().supportFragmentManager, "DialogInfoFragment")
        } 
    }

    override fun onDialogPostiveCLick(dialog: DialogFragment) {
        Log.i(TAG, "Listener returns a postive click")
    }
}

MyAlertDialog

class MyAlertDialog : DialogFragment() {
    
    // Use thsi instance for the interface
    internal var listener: MyAlertDialogListener

    // My Fragment implements this interface. 
    interface MyAlertDialogListener {
        onDialogPositiveClick(dialog: DialogFragment)
    }

   
    override fun onAttach(context: Context) {
        super.onAttach(context)
        // Verify  that the host implements the callback. 
        try {
            // My problem is here. 
            listener = context as MyAlertDailog
        } catch (e: ClassCastException) {
            // exception thrown here. 
            throw ClassCastException((context.toString() + " must implement MyAlertDailogListener")
        }
    }

    override fun onCreateDialog(savedInstanceState:Bundle?): Dialog {
        return activity?.let {
             val builder = AlertDialog.builder(it)
             ...
             builder.setPosiviveButton("Positive button",
               DialogInterface.OnClickListener {
                   listener.onDialogPositiveClick(this)     
             }
        }
    }

}

错误报告

    java.lang.ClassCastException: com.example.androiddevpractice.MainActivity@ab56136 must implement MyAlertDialogListener
        at com.example.androiddevpractice.topics.userinterface.dialog.MyAlertDialog.onAttach(MyAlertDialog.kt:35)

Answer 1

即使 launchAlertDialog() 方法在 MyFragment 内部，MyAlertDialog 的“宿主”是您的 Activity , 不是 MyFragment.

在 MainActivity 内实施 MyAlerDialog.MyAlertDialogListener 以使转换成功。如果需要，MainActivity 可以与 MyFragment 通信。

或者，您可以使用 setTargetFragment() 直接“连接”MyFragment 和 MyAlertDialog：

val dialog = MyAlertDialog()
dialog.setTargetFragment(this, 0)
dialog.show(requireActivity().supportFragmentManager, "DialogInfoFragment")

然后，不是重写 onAttach() 并转换上下文，而是转换 getTargetFragment():

的结果

builder.setPosiviveButton(
        "Positive button",
        DialogInterface.OnClickListener {
            val listener = targetFragment as MyAlertDialogListener
            listener.onDialogPositiveClick(this)     
        }
)

未附加 AlertDialog 侦听器

AlertDialog Listener not attached

android-alertdialog

kotlin