使用Fragment实现类似Tab的需求

大家都知道可以使用TabHost来实现， 不过这种实现已经是被deprecated, 其实是可以通过Fragment来实现， 不过如果是Fragment的话好像只能每次new一个fragment，这样感觉不太好， 按常理如果是以前有创建过fragment，下一次应该还是显示那个fragment实例。 通过google得知可以通过FragmentTransaction的attach和detach来实现。 下面贴下代码。

先detach所有可能的fragment，然后add或attach对应的fragment。

package com.kissbb.activity;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.widget.CompoundButton;
import android.widget.RadioButton;
import com.androidquery.AQuery;
import com.androidquery.util.AQUtility;
import com.kissbb.R;
import com.kissbb.api.GoodsAPI;
import com.kissbb.fragment.CartFragment;
import com.kissbb.fragment.KuaigouListFragment;
import com.kissbb.fragment.MoreFragment;
import com.kissbb.fragment.MyOrderFragment;
import com.kissbb.model.KuaigouGroup;
import de.greenrobot.event.util.AsyncExecutor;

import java.util.List;

public class MainActivity extends FragmentActivity implements CompoundButton.OnCheckedChangeListener {

    private RadioButton rbMenuIndex;
    private RadioButton rbMenuCart;
    private RadioButton rbMenuMyOrder;
    private RadioButton rbMenuMore;

    private View rlMenuIndex;
    private View rlMenuCart;
    private View rlMenuMyOrder;
    private View rlMenuMore;

    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        AQuery aq = new AQuery(this);

        rbMenuIndex = (RadioButton) findViewById(R.id.rbMenuIndex);
        rbMenuIndex.setOnCheckedChangeListener(this);
        rbMenuCart = (RadioButton) findViewById(R.id.rbMenuCart);
        rbMenuCart.setOnCheckedChangeListener(this);
        rbMenuMyOrder = (RadioButton) findViewById(R.id.rbMenuMyOrder);
        rbMenuMyOrder.setOnCheckedChangeListener(this);
        rbMenuMore = (RadioButton) findViewById(R.id.rbMenuMore);
        rbMenuMore.setOnCheckedChangeListener(this);

        rlMenuCart = findViewById(R.id.rlMenuCart);
        rlMenuIndex = findViewById(R.id.rlMenuIndex);
        rlMenuMore = findViewById(R.id.rlMenuMore);
        rlMenuMyOrder = findViewById(R.id.rlMenuMyOrder);

        //
        rbMenuIndex.setChecked(true);

//        CheckBox cbIndex = (CheckBox) findViewById(R.id.rbMenuIndex);
//        aq.id(R.id.rbMenuIndex).
//        aQuery.id(R.id.button).clicked(this, "buttonClicked");
    }

    public void buttonClicked(View view) {
        AsyncExecutor.create().execute(new AsyncExecutor.RunnableEx() {
            @Override
            public void run() throws Exception {
                List<KuaigouGroup> kuaigouList = new GoodsAPI(MainActivity.this).getKuaigouList();
                AQUtility.debug("List<KuaigouGroup> is not null: " + kuaigouList.size());
//                UserLoginResult userLoginResult = new GoodsAPI(MainActivity.this).userLogin("[email protected]", "87200795");
//                AQUtility.debug("UserLoginResult is not null: " + (userLoginResult != null));
//                new UserAPI(MainActivity.this).userRegister("[email protected]", "12345678", 111, 111, 11);
            }
        });
    }

    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if (isChecked) {
            resetAllRadioButtons();
            buttonView.setChecked(true);
            FragmentManager fragmentManager = getSupportFragmentManager();
            KuaigouListFragment kuaigouListFragment = (KuaigouListFragment) fragmentManager.findFragmentByTag(String.valueOf(R.id.rbMenuIndex));
            CartFragment cartFragment = (CartFragment) fragmentManager.findFragmentByTag(String.valueOf(R.id.rbMenuCart));
            MyOrderFragment myOrderFragment = (MyOrderFragment) fragmentManager.findFragmentByTag(String.valueOf(R.id.rbMenuMyOrder));
            MoreFragment moreFragment = (MoreFragment) fragmentManager.findFragmentByTag(String.valueOf(R.id.rbMenuMore));
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            /** Detaches all fragments if exists */
            if (kuaigouListFragment != null) {
                fragmentTransaction.detach(kuaigouListFragment);
            }
            if (cartFragment != null) {
                fragmentTransaction.detach(cartFragment);
            }
            if (myOrderFragment != null) {
                fragmentTransaction.detach(myOrderFragment);
            }
            if (moreFragment != null) {
                fragmentTransaction.detach(moreFragment);
            }
            int buttonId = buttonView.getId();
            switch (buttonId) {
                case R.id.rbMenuIndex:
                    rlMenuIndex.setBackgroundResource(R.drawable.footover);
                    if (kuaigouListFragment == null) {
                        /** Create AndroidFragment and adding to fragmenttransaction */
                        fragmentTransaction.add(R.id.flContent, new KuaigouListFragment(), String.valueOf(R.id.rbMenuIndex));
                    } else {
                        /** Bring to the front, if already exists in the fragmenttransaction */
                        fragmentTransaction.attach(kuaigouListFragment);
                    }
                    break;
                case R.id.rbMenuCart:
                    rlMenuCart.setBackgroundResource(R.drawable.footover);
                    if (cartFragment == null) {
                        /** Create AndroidFragment and adding to fragmenttransaction */
                        fragmentTransaction.add(R.id.flContent, new CartFragment(), String.valueOf(R.id.rbMenuCart));
                    } else {
                        /** Bring to the front, if already exists in the fragmenttransaction */
                        fragmentTransaction.attach(cartFragment);
                    }
                    break;
                case R.id.rbMenuMore:
                    rlMenuMore.setBackgroundResource(R.drawable.footover);
                    if (moreFragment == null) {
                        /** Create AndroidFragment and adding to fragmenttransaction */
                        fragmentTransaction.add(R.id.flContent, new MoreFragment(), String.valueOf(R.id.rbMenuMore));
                    } else {
                        /** Bring to the front, if already exists in the fragmenttransaction */
                        fragmentTransaction.attach(moreFragment);
                    }
                    break;
                case R.id.rbMenuMyOrder:
                    rlMenuMyOrder.setBackgroundResource(R.drawable.footover);
                    if (myOrderFragment == null) {
                        /** Create AndroidFragment and adding to fragmenttransaction */
                        fragmentTransaction.add(R.id.flContent, new MyOrderFragment(), String.valueOf(R.id.rbMenuMyOrder));
                    } else {
                        /** Bring to the front, if already exists in the fragmenttransaction */
                        fragmentTransaction.attach(myOrderFragment);
                    }
                    break;
            }
            fragmentTransaction.commit();
        }
    }

    private void resetAllRadioButtons() {
        rbMenuCart.setChecked(false);
        rbMenuIndex.setChecked(false);
        rbMenuMore.setChecked(false);
        rbMenuMyOrder.setChecked(false);
        rlMenuMore.setBackgroundResource(R.drawable.footline);
        rlMenuIndex.setBackgroundResource(R.drawable.footline);
        rlMenuMyOrder.setBackgroundResource(R.drawable.footline);
        rlMenuCart.setBackgroundResource(R.drawable.footline);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if(isTaskRoot()){

            //clean the file cache with advance option
            long triggerSize = 3000000; //starts cleaning when cache size is larger than 3M
            long targetSize = 2000000;      //remove the least recently used files until cache size is less than 2M
            AQUtility.cleanCacheAsync(this, triggerSize, targetSize);
        }
    }
}

但是如果attach已经存在的fragment时  还是会调用Fragment的onCreateView方法， 这样的话会让整个fragment重新绘制UI， 如果是里面是个ListView的话，因为需要重新所以ListView滚动那个位置就丢失了，如何能避免这个问题呢？ 那就要保存Fragment onCreateView中生成的view， 代码如下。

package com.kissbb.fragment;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.DisplayMetrics;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.widget.ListView;
import com.androidquery.util.AQUtility;
import com.handmark.pulltorefresh.library.PullToRefreshBase;
import com.handmark.pulltorefresh.library.PullToRefreshListView;
import com.kissbb.R;
import com.kissbb.adapter.KuaigouListAdapter;
import com.kissbb.api.GoodsAPI;
import com.kissbb.model.KuaigouGroup;
import de.greenrobot.event.EventBus;
import de.greenrobot.event.util.AsyncExecutor;

import java.util.List;

/**
 * Created with IntelliJ IDEA.
 * User: Denny
 * Date: 13-7-17
 * Time: 下午11:00
 * To change this template use File | Settings | File Templates.
 */
public class KuaigouListFragment extends Fragment {

    private GoodsAPI goodsAPI;
    private PullToRefreshListView ptrlvKuaigou;
    private int imgHeight;

    private List<KuaigouGroup> kuaigouGroupList;

    private View rootView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EventBus.getDefault().register(this);
        goodsAPI = new GoodsAPI(getActivity());
        DisplayMetrics dm = getResources().getDisplayMetrics();
        int widthPixels = dm.widthPixels;
        imgHeight = (int) (182f/713*widthPixels);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        EventBus.getDefault().unregister(this);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        AQUtility.debug("onCreateView", "KuaigouListFragment");
        if (rootView == null) {
            rootView = inflater.inflate(R.layout.kuaigoulist_fragment, container, false);
            ptrlvKuaigou = (PullToRefreshListView) rootView.findViewById(R.id.ptrlvKuaigou);
            ptrlvKuaigou.setOnRefreshListener(new PullToRefreshBase.OnRefreshListener<ListView>() {
                @Override
                public void onRefresh(PullToRefreshBase<ListView> refreshView) {
                    startToPrepareData();
                }
            });

            if (kuaigouGroupList != null) {
            }else{
                ptrlvKuaigou.setVisibility(View.INVISIBLE);
                startToPrepareData();
            }
        }

        //缓存的rootView需要判断是否已经被加过parent， 如果有parent需要从parent删除，要不然会发生这个rootview已经有parent的错误。
        ViewGroup parent = (ViewGroup) rootView.getParent();
        if (parent != null) {
            parent.removeView(rootView);
        }
        return rootView;
    }

    private void startToPrepareData() {
        AsyncExecutor.create().execute(new AsyncExecutor.RunnableEx() {
            @Override
            public void run() throws Exception {
                getKuaigouListData();
            }
        });
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);    //To change body of overridden methods use File | Settings | File Templates.
        AQUtility.debug("onActivityCreated", "KuaigouListFragment");
    }

    public void onEventMainThread(KuaigouDataEvent event) {
        ptrlvKuaigou.setVisibility(View.VISIBLE);
        kuaigouGroupList = event.kuaigouList;
        ptrlvKuaigou.setAdapter(new KuaigouListAdapter(kuaigouGroupList, getActivity(), imgHeight));
        ptrlvKuaigou.onRefreshComplete();
    }

    private void getKuaigouListData() {
        List<KuaigouGroup> kuaigouList = goodsAPI.getKuaigouList();
        EventBus.getDefault().post(new KuaigouDataEvent(kuaigouList));
    }

    public class KuaigouDataEvent{
        public List<KuaigouGroup> kuaigouList;

        public KuaigouDataEvent(List<KuaigouGroup> kuaigouList) {
            this.kuaigouList = kuaigouList;
        }
    }
}

特别注意这段代码， 需要先把view从parent中删掉 才能加回去。

        //缓存的rootView需要判断是否已经被加过parent， 如果有parent需要从parent删除，要不然会发生这个rootview已经有parent的错误。
        ViewGroup parent = (ViewGroup) rootView.getParent();
        if (parent != null) {
            parent.removeView(rootView);
        }