Android 中Fragment和Activity之间的通信

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ContainerActivity"
    android:orientation="vertical"
    >
    <TextView
        android:id="@+id/tv_container"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="hello"
        android:textColor="@color/black"
        android:textSize="20sp"
        android:gravity="center"
        />
    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/fl_container"
        />
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <Button
        android:id="@+id/btn_change"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="更改Activity中的字体" />
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="这是一个Fragment" />
</LinearLayout>

public class ContainerActivity extends AppCompatActivity implements FirstFragment.ChangeListener {
    private FrameLayout fl_container;
    private TextView tv_container;
    private FirstFragment firstFragment;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_container);
        fl_container = findViewById(R.id.fl_container);
        tv_container = findViewById(R.id.tv_container);
        //实例化Fragment
        firstFragment = new FirstFragment();
        //将Fragment添加到Activity中 使用commitAllowingStateLoss容错率更高 建议使用这个
        getSupportFragmentManager().beginTransaction().add(R.id.fl_container,firstFragment).commitAllowingStateLoss();
    }
    @Override
    public void setData(String text) {
        tv_container.setText(text);
    }
}

public class FirstFragment extends Fragment {
    private Button btn_change;
    private ChangeListener listener;
    //构建Fragment中的视图
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment,container,false);
        return view;
    }
    //视图创建完成之后 在这个方法面里面做一些初始化的工作
    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        btn_change = view.findViewById(R.id.btn_change);
        btn_change.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                listener.setData("你好");
            }
        });
    }
    //创建一个接口
    public interface ChangeListener{
        void setData(String text);
    }
  //当Fragment和Activity建立关联的时候调用
    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        try {
            listener= (ChangeListener) context;
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}