Fragment

 

建立ContainerActivity.java文件添加AFragment并且用BFragment替换：

public class ContainerActivity extends AppCompatActivity {
    private AFragment aFragment;
    private BFragment bFragment;
    private Button BtnChange;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_container);
        BtnChange=findViewById(R.id.btn_change);
        BtnChange.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(bFragment==null){
                    bFragment=new BFragment();//实例化BFragment
                }
                getSupportFragmentManager().beginTransaction().replace(R.id.f1_container,bFragment).commitAllowingStateLoss();
            }
        });//用bFragment替换到Activity中去

        aFragment=new AFragment();//实例化AFragment
        getSupportFragmentManager().beginTransaction().add(R.id.f1_container,aFragment).commitAllowingStateLoss();
        //把AFragment添加到Activity中，记得调用commit
    }
}

 

然后对应的activity_container.xml文件：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/btn_change"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="更换fragment"/>

    <FrameLayout
        android:id="@+id/f1_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/btn_change"/>
</RelativeLayout>

然后是AFragment.java文件，继承的是Fragment，不是AppCompatActivity：

public class AFragment extends Fragment {
    private TextView TVtitle;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view= inflater.inflate(R.layout.fragment_a,container,false);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        TVtitle=view.findViewById(R.id.tv_title);
    }
}

对应的fragment_a.xml文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center">
    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="@color/black"
        android:textSize="20sp"
        android:text="我是AFragment!"
        android:gravity="center"/>
</LinearLayout>

最后就是BFragment.java文件和fragment_b.xml文件和A差不多，就是改了个字母（把b换成a）而已。