或者像下面这样共享ViewModel:

public class SharedViewModel extends ViewModel {
    private final MutableLiveData<Item> selected = new MutableLiveData<Item>();

    public void select(Item item) {
        selected.setValue(item);
    }

    public LiveData<Item> getSelected() {
        return selected;
    }
}


public class MasterFragment extends Fragment {
    private SharedViewModel model;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
        itemSelector.setOnClickListener(item -> {
            model.select(item);
        });
    }
}

public class DetailFragment extends Fragment {
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        SharedViewModel model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
        model.getSelected().observe(this, { item ->
           // Update the UI.
        });
    }
}

https://developer.android.com/topic/libraries/architecture/viewmodel#sharing_data_between_fragments

不同的方法，允许一个片段与它的活动通信:

1)在片段中定义一个公共接口，并为其创建一个变量

public OnFragmentInteractionListener mCallback;

public interface OnFragmentInteractionListener {
    void onFragmentInteraction(int id);
}

2)将活动转换为片段中的mCallback变量

try {
    mCallback = (OnFragmentInteractionListener) getActivity();
} catch (Exception e) {
    Log.d(TAG, e.getMessage());
}

3)在你的活动中实现监听器

public class MainActivity extends AppCompatActivity implements DFragment.OnFragmentInteractionListener  {
     //your code here
}

4)在活动中覆盖OnFragmentInteraction

@Override
public void onFragmentInteraction(int id) {
    Log.d(TAG, "received from fragment: " + id);
}

更多信息:https://developer.android.com/training/basics/fragments/communicating.html

使用这个AppDialog类既可以将数据传递到DialogFragment，也可以从中获取结果。

详细解释:

Premise - Fragments get destroyed and recreated on config changes. View models hang around. When using a Dialog, it is recommended to wrap it in DialogFragment so that when the user rotates device and changes orientation the Dialog will not unexpectedly disappear (the DialogFragment will re-create it and re-display it). Limitation (hence this question) - The way the DialogFragment works is it takes a class that it will need to re-instantiate on configuration changes - that means one can't have constructor parameters to the subclass to pass parameters, and typically one needs to make custom callbacks through a view model to pass back result of dialog. That typically means a new subclass for every dialog. The solution - To help with all this, this custom AppDialog fragment comes to the rescue - the parameters are stored in-memory (similar to view model, you can think of it as a tiny custom view model that holds T in memory and uses it to re-create the dialog on config changes) until the dialog fragment is dismissed. The proper way to call back would be through a view model. If the fragment that shows the AppDialog, then you probably already have a view model and you can reference it from the lambda used to create the dialog - that means additional strong reference to the view model until the dialog fragment is dismissed. Example - see the examples where a simple Dialog is refactored to use this AppDialog utility class to both receive a parameter and do a callback to viewModel to notify of result.

helper类:

class AppDialog<T>: DialogFragment() {
    companion object {

        fun<T> buildDialog(params: T? = null, builder: AppDialogLambda<T>): AppDialog<T> {

            // Setup arguments
            val args = Bundle()
            args.putInt("key", pushDialogArgs(params, builder))

            // Instantiate
            val fragment = AppDialog<T>()
            fragment.arguments = args
            return fragment
        }

        // --------------------
        // Dialog Arguments

        private var lastKey: Int = 0
        private val dialogArgs = mutableMapOf<Int, Pair<Any?, AppDialogLambda<*>>>()

        private fun pushDialogArgs(params: Any?, builder: AppDialogLambda<*>): Int {
            dialogArgs[lastKey] = params to builder
            return lastKey++
        }

        private fun getDialogArgs(key: Int): Pair<Any?, AppDialogLambda<*>> {
            return dialogArgs[key]!!
        }

        private fun deleteDialogArgs(key: Int) {
            dialogArgs.remove(key)
        }
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        // Get arguments
        val argKey = requireArguments().getInt("key")
        val (params, builder) = getDialogArgs(argKey)

        // We are getting back our arguments we passed AppDialog.buildDialog and
        // the type is guaranteed to be the same. Silence this warning
        @Suppress("UNCHECKED_CAST")
        return (builder as AppDialogLambda<T>)(this, params as T?)
    }

    override fun onDismiss(dialog: DialogInterface) {
        super.onDismiss(dialog)
        val argKey = requireArguments().getInt("key")
        deleteDialogArgs(argKey)
    }
}

示例用法(之后):

        val info = mapOf("message" to "${error.description}\n\nPlease check your Internet connection and try again.")
        AppDialog.buildDialog(info) { fragment, params ->
            fragment.isCancelable = false // since we are in a DialogFragment
            AlertDialog.Builder(fragment.context)
                .setTitle("Terms Of Service Failed To Load")
                .setMessage(params!!["message"])
                .setPositiveButton("Retry") { _, _ ->
                    // Update the view model instead of calling UserTOSFragment directly 
                    // as the fragment may be destroyed and recreated
                    // on configuration changes. The viewModel will stay alive.
                    viewModel.onTermsOfServiceReload()
                }
                .setNegativeButton("Cancel") { _, _ ->
                    viewModel.onTermsOfServiceDeclined()
                    fragment.findNavController().popBackStack()
                }.create()
        }.show(parentFragmentManager, "TOS Failed Dialog")

用法示例(前): 如果不使用DialogFragment(为了说明目的，不要这样做，这是不好的做法，因为对话框将在配置更改时被销毁)，则UserTOSFragment中的代码。kt -用于在重试时直接调用UserTOSFragment.loadContent()的注释代码。在上面的例子中，这必须重写为调用viewModel.onTermsOfServiceDeclined():

        AlertDialog.Builder(context)
            .setTitle("Terms Of Service Failed To Load")
            .setMessage("${error.description}\n\nPlease check your Internet connection and try again.")
            .setPositiveButton("Retry") { _, _ ->
                loadContent()
            }
            .setCancelable(false)
            .setNegativeButton("Cancel") { _, _ ->
                viewModel.onTermsOfServiceDeclined()
                findNavController().popBackStack()
            }
            .show()

对于还在阅读这篇文章的人:setTargetFragment()已被弃用。现在建议像这样使用FragmentResultListener API:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setFragmentResultListener("requestKey") { key, bundle ->
        val result = bundle.getString("resultKey")
        // Do something with the result...
    }

    ...

    // Somewhere show your dialog
    MyDialogFragment.newInstance().show(parentFragmentManager, "tag")
}

然后在你的MyDialogFragment中设置结果:

button.setOnClickListener{
    val result = "some string"
    setFragmentResult("requestKey", bundleOf("resultKey" to result))
    dismiss()
}

使用myDialogFragment。setTargetFragment(this, MY_REQUEST_CODE)从你显示对话框的地方，然后当你的对话框完成时，从它可以调用getTargetFragment().onActivityResult(getTargetRequestCode()，…)，并在包含的片段中实现onActivityResult()。

这似乎是对onActivityResult()的滥用，特别是因为它根本不涉及活动。但我看到官方谷歌的人推荐它，甚至可能在api演示中。我认为这是g/setTargetFragment()被添加的原因。

或者像下面这样共享ViewModel:

public class SharedViewModel extends ViewModel {
    private final MutableLiveData<Item> selected = new MutableLiveData<Item>();

    public void select(Item item) {
        selected.setValue(item);
    }

    public LiveData<Item> getSelected() {
        return selected;
    }
}


public class MasterFragment extends Fragment {
    private SharedViewModel model;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
        itemSelector.setOnClickListener(item -> {
            model.select(item);
        });
    }
}

public class DetailFragment extends Fragment {
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        SharedViewModel model = ViewModelProviders.of(getActivity()).get(SharedViewModel.class);
        model.getSelected().observe(this, { item ->
           // Update the UI.
        });
    }
}

https://developer.android.com/topic/libraries/architecture/viewmodel#sharing_data_between_fragments