Fragement (一)

• Fragment 有自己的生命周期

• Fragment依赖于Activity

• Fragment通过 getActivity() 可以获取所在的Activity；

• Activity通过FragmentManager的 findFragmentById()或findFragmentByTag 获取Fragment

• Fragment和Activity是多对多的关系

1. 创建装在Fragment的ContainerActivity

java 代码:ContainerActivity.class

public class ContainerActivity extends AppCompatActivity {
    private  AFragment aFragment;
    private  BFragment bFragment;
    private Button btn_change;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_container);
        //实现点击按钮由A碎片转换到B碎片
        btn_change = (Button) findViewById(R.id.btn_change);
        btn_change.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(bFragment == null){
                    bFragment=new BFragment();
                }
                getSupportFragmentManager().beginTransaction().replace(R.id.fl_container,bFragment).commitAllowingStateLoss();
            }
        });
        //把AFragment添加到Activity中,记得调用commit
        //R.id.fl_container:装在fragment的容器
        //aFragment：要加载的fragment
        aFragment=new AFragment();
        getSupportFragmentManager().beginTransaction().add(R.id.fl_container,aFragment).commitAllowingStateLoss();

    }
}

关键代码

1. 先实例化单个Fragment
2. 调用getSupportFragment方法里的beginTransaction（）方法去向指定容器添加aFragament
3. 最后调用commitAllowingStateLoss()方法

//R.id.fl_container:装在fragment的容器
//aFragment：要加载的fragment

aFragment=new AFragment();   
getSupportFragmentManager().beginTransaction().add(R.id.fl_container,aFragment).commitAllowingStateLoss();

xml 代码:activity_container.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 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/fl_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/btn_change"/>

</RelativeLayout>

2.创建Fragment（AFragment和BFragment完全相同）

java 代码： AFragment.class

public class BFragment extends Fragment {
    private TextView mTvTitle;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        //相当于activity的onCreate里的setcontentView,给它一个布局文件返回一个视图文件
        View view=inflater.inflate(R.layout.fragment_b,container,false);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        //当View创建完成后，这里有一个回调方法
        super.onViewCreated(view, savedInstanceState);
        mTvTitle=(TextView)view.findViewById(R.id.tv_title);
    }
}

xml 代码:fragment_b.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center">
    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="#000"
        android:textSize="20sp"
        android:text="我是BFragment"
        android:gravity="center"/>

</LinearLayout>