今天跟大家分析個人對fragment用法的理解

1.Fragment起源

迄今為止,android的設(shè)備越來越多,大到智能平板和電視,小到手機(jī)甚至是智能手表,這些設(shè)備因為px的不同而需要針對各種機(jī)型進(jìn)行適配,而fragment最初在Android3.0出就是針對平板的,在到4.0的時候就開始和手機(jī)整合使得Android的app能運(yùn)行各種各樣的屏幕上.而且fragment的動態(tài)改變也使得大多數(shù)開發(fā)者對它情有獨鐘,使用fragment的應(yīng)用也越來越多,下面就跟大家粗略的介紹一下fragment的用法以及生命周期在不同的情況會發(fā)生怎樣的變化.

2.Fragment的生命周期

大部分人一談到fragment的生命周期,肯定是先上一張跟Activity一樣惡心的圖片,先不說新手能不能記清楚上面的是一個個生命周期方法,單單是英文就惡心到當(dāng)初看它的我了.不過,我還是得上這么一張圖片詳細(xì)解釋一下為何有這么多的生命周期,這些生命周期又是在什么時候調(diào)用的.

Fragment的生命周期-Xxuserwing.png

onAttach() --- onDetach()
onCreate() --- onDestroy()
onCreateView() --- onDestroyView()
onStart() --- onStop()
onResume() --- onPause()

3.Fragment的創(chuàng)建

Fragment是依附于Activity的,所以你要使用Fragment你就必須要有Activity,話不多說直接擼代碼.

3.1 Fragment4Code

通過代碼的方式在Activity載入Fragment
//R.id.container 為Activity的布局文件中的占位容器

getFragmentManager()
        .beginTransaction() //事務(wù)
        .addToBackStack(null) //回退棧
         //.replace(R.id.container, new FirstFragment()) 替換
        .add(R.id.container, new FirstFragment()) //添加
        .commit(); //提交

3.2 Fragment4XML

通過XML直接添加

<fragment
        android:id="@+id/fragment"  //id
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:name="packageName.FirstFragment"/>

4.Fragment回退棧

通過回退棧,讓用戶點擊回退鍵的時候先將棧內(nèi)fragment彈棧后再退出

//創(chuàng)建第一個fragment
public class frangment_fir extends Fragment {
@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return View.inflate(getActivity(), R.layout.fragment_item, null);
    }
       
    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Button bt_1 = (Button) view.findViewById(R.id.bt_1);
        bt_1.setOnClickListener(new View.OnClickListener() {
          //**設(shè)置點擊監(jiān)聽 添加加入到回退棧的fragment_sec**
            @Override
            public void onClick(View v) {
                getFragmentManager()
                .beginTransaction()
                .addToBackStack(null)   //將fragment_sec加入到默認(rèn)的回退棧中
                .replace(R.id.container, new frangment_sec())
                .commit();
            }
        });
    }
}

//創(chuàng)建第二個fragment
public class frangment_sec extends Fragment {
@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return View.inflate(getActivity(), R.layout.fragment_item_sec, null);
    }
}

//在MainActivity 添加fragment_fir;
public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getFragmentManager()
                .beginTransaction()
                .add(R.id.container, new frangment_one())
                .commit();
    }
}

需要補(bǔ)充的是:

當(dāng)fragment_sec是回退棧添加的時候 再次按下回退鍵的時候,**fragment_fir不走onAttach(),onCreate(),onDestroy(),onDetach()這幾個方法 **,所以使用的時候可以根據(jù)需求將一次加載數(shù)據(jù)方法放入其中,而多次加載數(shù)據(jù)方法規(guī)避這幾個方法.

5.Fragment與Activity之間的通訊

5.1點擊切換fragment

通過點擊不同RadioGroup中的button來切換Fragment

public class MainActivity extends Activity implements OnCheckedChangeListener {
    private RadioGroup rg;
    private List<Fragment> fragments;
    private int preIndex;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        rg = (RadioGroup) findViewById(R.id.rg);
        rg.setOnCheckedChangeListener(this);
        initData();
    }
    //初始化添加三個不同fragment到集合中
    private void initData() {
        fragments = new ArrayList<>();
        fragments.add(new Fragment1());
        fragments.add(new Fragment2());
        fragments.add(new Fragment3());
    }

    @Override
    public void onCheckedChanged(RadioGroup group, int checkedId) {
        switch (checkedId) {
        case R.id.rb1:
            changeFragment(0);
            break;
        case R.id.rb2:
            changeFragment(1);
            break;
        case R.id.rb3:
            changeFragment(2);
            break;
        default:
            break;
        }
    }
    //定義改變fragment的方法 當(dāng)點擊不同fragment對應(yīng)的raidobutton時候進(jìn)行切換
    private void changeFragment(int index) {
        Fragment fragment = fragments.get(index);
        FragmentTransaction ft = getFragmentManager().beginTransaction();
        if (!fragment.isAdded()) {
            ft.add(R.id.container, fragment);
        }
        ft.hide(fragments.get(preIndex));
        ft.show(fragment);
        ft.commit();
        preIndex = index;
    }
}

5.2 :Fragment2Activity(最早的方法,不推薦使用)

下列代碼可以用接口回調(diào)實現(xiàn)(接口回調(diào)被放在5.2.2中實fragment2fragment)

public class MainActivity extends Activity {

    private Button bt_activity;
    private Myfragment fragment;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bt_activity = (Button) findViewById(R.id.bt_activity);
        
    }

    public void click(View view) {
        if (fragment == null ) {
            fragment = new Myfragment();
            Bundle args = new Bundle();
            args.putString("key", "Activity2Fragment");
            fragment.setArguments(args);
            getFragmentManager().beginTransaction().addToBackStack(null)
            .add(R.id.container, fragment).commit();
        }
    }

    public void transformGift(String text) {
        bt_activity.setText(text);
    }
}

public class Myfragment extends Fragment {
    private View view;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        if (view == null) {
            view = View.inflate(getActivity(), R.layout.fragment_item,
                    null);
        }
        return view;
    }
    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Bundle bundle = getArguments();
        final String string = bundle.getString("key");
        Button bt = (Button) view.findViewById(R.id.bt);
        bt.setText(string);
        bt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            //通過獲取依附的Activity進(jìn)行強(qiáng)轉(zhuǎn)調(diào)用(耦合性太強(qiáng),不推薦使用)
            ((MainActivity) getActivity()).transformGift("Fragment2Activity");  
            }
        });
    }
}

5.3 :接口回調(diào)實現(xiàn)Fragment2Fragment

使用接口回調(diào)來實現(xiàn)依附在同一個Activity的Fragment之間的通訊.
將2個fragment放入mainActivity兩個平分容器中.

//左邊的Fragment
public class Fragment_left extends Fragment implements OnItemClickListener {
    private ListView ll_left;
    private String[] item ="XXX,XXX,XXX,XXX,XXX".split(",");  // 具體名字忽略.
    private OnGetResultListener listener;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return View.inflate(getActivity(), R.layout.left_item, null);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        ll_left = (ListView) view.findViewById(R.id.ll_left);
        ll_left.setAdapter(new ArrayAdapter<>(getActivity(),
                android.R.layout.simple_list_item_1, item));
        ll_left.setOnItemClickListener(this);
    }


    public void setOnGetResultListener(OnGetResultListener listener) {
        this.listener = listener;
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {
        if (listener != null) {
            listener.onGetResult(item[position]);
        }
    }
}

//右邊的fragment
public class Fragment_right extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return View.inflate(getActivity(), R.layout.right_item, null);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Bundle bundle = getArguments();
        if (bundle != null) {
            String string = bundle.getString("data");
            ((TextView) view.findViewById(R.id.tv)).setText(string+"灰常漂亮!!!");
        }
    }
}

//MainActivity 用于充當(dāng)fragment交互的橋梁
public class MainActivity extends Activity implements OnGetResultListener {

    private Fragment_left fragment_left;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Fragment_left = new Fragment_left();
        fragment_left.setOnGetResultListener(this);
        getFragmentManager().beginTransaction()
                .replace(R.id.left_container, fragment_left)
                .replace(R.id.right_container, new fragment_right()).commit();
    }

    @Override
    public void onGetResult(String string) {
        Fragment_right fragment = new Fragment_right();
        Bundle args = new Bundle();
        args.putString("data", string);
        fragment.setArguments(args);
        getFragmentManager().beginTransaction()
                .replace(R.id.right_container, fragment).commit();
    }
}

5.4 :使用otto框架(Bus)

使用前導(dǎo)入otto的jar包并單例Bus

// 單例Bus
import com.squareup.otto.Bus;

public class busFactory {
    public static Bus bus = new Bus();

    private busFactory() {
    }

    public static Bus getBus() {
        return bus;
    }
}

//左邊的Fragment
public class Fragment_left extends Fragment implements OnItemClickListener {
    private ListView ll_left;
    private String[] item = "碧瑤,陸雪琪,小龍女,李莫愁,王語嫣,李滄海,趙敏,周芷若,小昭,鷹離".split(",");

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return View.inflate(getActivity(), R.layout.left_item, null);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        ll_left = (ListView) view.findViewById(R.id.ll_left);
        ll_left.setAdapter(new ArrayAdapter<>(getActivity(),
                android.R.layout.simple_list_item_1, item));
        ll_left.setOnItemClickListener(this);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {
        Bus bus = busFactory.getBus();
        bus.post(item[position]);

    }

}

//右邊Fragment
public class Fragment_right extends Fragment {
    private TextView tv;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        busFactory.getBus().register(this); //注冊
        return View.inflate(getActivity(), R.layout.right_item, null);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        busFactory.getBus().unregister(this); //注銷
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        tv = (TextView) view.findViewById(R.id.tv);
    }

    @Subscribe    //注解來實現(xiàn)數(shù)據(jù)傳遞 
    public void setData(String text) {//參數(shù)可以是Bus.post傳入?yún)?shù)的類型或者父類類型(Object);
        tv.setText(text + "text");
    }
}

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getFragmentManager().beginTransaction()
                .replace(R.id.left_container, new Fragment_left())
                .replace(R.id.right_container, new Fragment_right()).commit();
    }
}

總結(jié):

其實開發(fā)中用到的時候大多數(shù)都是用的接口回調(diào)或者otto ,但是個人在開發(fā)中發(fā)現(xiàn)用接口回調(diào)的時候,會出現(xiàn)畫面數(shù)據(jù)重疊Bug.而用EventBus就可以避免了這類Bug,所以推薦大家在使用的時候最好還是使用Bus來進(jìn)行通訊.