我有两个片段，我想在我的屏幕上逐一显示它们。它们由mainactivity管理。第一个片段包含一个textview和一个按钮。第二个片段包含一个edittext和一个按钮。我试图做的是：第一个片段显示在屏幕上，当用户按下按钮时，我希望我的活动显示第二个片段，当用户按下此片段中的按钮时，我希望将文本从edittext发送到第一个片段，并在textview上显示。我为听众使用了这个界面。

public class MainActivity extends AppCompatActivity implements Listener, ListenerTwo{

FragmentTransaction fragmentTransaction;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    fragmentTransaction =  getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.fragmentPlaceholder, new FragmentOne());
    fragmentTransaction.commit();

}

@Override
public void onButtonSelected() {
    fragmentTransaction =  getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.fragmentPlaceholder, new FragmentTwo());
    fragmentTransaction.commit();
}

@Override
public void onButtonPressed(String text) {
    FragmentOne fragmentOne = (FragmentOne)getSupportFragmentManager().findFragmentById(R.id.fragmentPlaceholder);

    if (fragmentOne != null)
        fragmentOne.setTextt(text);
}

}
在我的片段中：

public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    Button button = view.findViewById(R.id.button);
    textView = view.findViewById(R.id.textView);
    Listener listener = (Listener) getActivity();

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Toast.makeText(getContext(), "button clicked", Toast.LENGTH_SHORT).show();
            if (listener != null)
                listener.onButtonSelected();
        }
    });

}

public void setTextt (String text) {
    textView.setText(text);
}

第二部分：

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    Button button = view.findViewById(R.id.button2);
    EditText editText = view.findViewById(R.id.editText);
    ListenerTwo listener = (ListenerTwo) getActivity();

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Toast.makeText(getContext(), "button clicked", Toast.LENGTH_SHORT).show();
            if (listener != null)
                listener.onButtonPressed(editText.getText().toString());
        }
    });

}