天哥视频笔记

• Fragment和Activity的通信

  1. 在AFragment中定义一个IOnMessageClick接口

  2. 在ContainerActivity中实现接口

java 代码:AFragment.class

public class AFragment extends Fragment {
    private TextView mTvTitle;
    private Button btn_change;
    private Button btn_reset;
    private  BFragment bFragment;
    private Button btn_message;
    private IOnMessageClick listener;

    public static AFragment newInstance(String title){
        AFragment fragment=new AFragment();
        Bundle bundle=new Bundle();
        bundle.putString("title",title);
        fragment.setArguments(bundle);
        return fragment;
    }

    public interface IOnMessageClick{
        void onClick(String text);
}

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        try {
        listener=(IOnMessageClick) context;

        }catch(ClassCastException e){
            throw new ClassCastException("Activity必须实现IOnMessageClick接口");
        }
        
    }


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.fragment_a,container,false);
        Log.d("AFragment","-------onCreateView-------");
        return view;
    }


    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        mTvTitle=(TextView)view.findViewById(R.id.tv_title);
        btn_change = (Button)view.findViewById(R.id.btn_change);
        btn_reset = (Button) view.findViewById(R.id.btn_reset);
        btn_message = (Button) view.findViewById(R.id.btn_message);
        btn_message.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //通过getActivity转成ContainerActivity，然后调用ContainerActivity里面的setData方法
//                ((ContainerActivity)getActivity()).setData("你好");
                listener.onClick("你好");
            }
        });
        btn_change.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(bFragment == null){
                    bFragment=new BFragment();
                }
                Fragment fragment=getFragmentManager().findFragmentByTag("a");
                if(fragment!=null){ 
                    getFragmentManager().beginTransaction().hide(fragment).add(R.id.fl_container,bFragment).addToBackStack(null).commitAllowingStateLoss();
                }else{
 getFragmentManager().beginTransaction().replace(R.id.fl_container,bFragment).addToBackStack(null).commitAllowingStateLoss();

                }

            }
        });
        btn_reset.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mTvTitle.setText("我是新文字");
            }
        });

        if(getArguments()!=null){
 mTvTitle.setText(getArguments().getString("title"));
        }

    }
}

关键代码1

1. 定义一个IOnMessageClick接口，实现点击传值
2. 在onAttach中，把context强制转换成IOnMessage接口，如果转换失败代表context的那个activity就有没有实现这个接口，这时就抛出异常

    public interface IOnMessageClick{
        void onClick(String text);
}

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        try {
            listener=(IOnMessageClick) context;
        }catch(ClassCastException e){
            throw new ClassCastException("Activity必须实现IOnMessageClick接口");
        }
        
    }

关键代码2

1. 点击按钮时就能调用接口的onClick方法，传递数据传到activity中

  listener.onClick("你好");

xml 代码:fragment_a.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">
    <Button
        android:id="@+id/btn_message"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="给Activity传递消息"
        android:textAllCaps="false"/>
    <Button
        android:id="@+id/btn_change"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="更换为BFragment"
        android:textAllCaps="false"/>
    <Button
        android:id="@+id/btn_reset"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="更换为TextView的文字内容"
        android:textAllCaps="false"/>
    <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AFragment"
        android:gravity="center"/>

</LinearLayout>

java 代码:ContentActivity.class

public class ContainerActivity extends AppCompatActivity implements AFragment.IOnMessageClick{
    private  AFragment aFragment;
    private TextView tv_title;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_container);
        tv_title = (TextView) findViewById(R.id.tv_title);
        aFragment=AFragment.newInstance("我是参数");
        getSupportFragmentManager().beginTransaction().add(R.id.fl_container,aFragment,"a").commitAllowingStateLoss();
    }

    @Override
    public void onClick(String text) {
        tv_title.setText(text);
    }
}

关键代码1

1. 实现IOnMessageClick接口

public class ContainerActivity extends AppCompatActivity implements AFragment.IOnMessageClick{
  @Override
    public void onClick(String text) {
        tv_title.setText(text);
    }
}

xml 代码:content_activity.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">
    <TextView
        android:id="@+id/tv_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="20sp"
        android:textColor="#000"
        android:text="Hello"/>

    <FrameLayout
        android:id="@+id/fl_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/tv_title"
        />

</RelativeLayout>