package com.mine.fragmentdemo;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import
 
 android.widget.TextView;

import static com.mine.fragmentdemo.FragmentFactory.F1;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private TextView tv1;
    private TextView tv2;
    private TextView tv3;
    private FragmentManager mFragmentManager;
    private
 
 Fragment mFragment1;
    private Fragment mFragment2;
    private Fragment mFragment3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv1 = (TextView) findViewById(R.id.tv1);
        tv2 = (TextView) findViewById(R.id.tv2);
        tv3 = (TextView) findViewById(R.id.tv3);
        tv1.setOnClickListener(this
 
);
        tv2.setOnClickListener(this);
        tv3.setOnClickListener(this);
        /*
        * Fragment重疊原因一
        * 1.Activity橫豎屏切換(或者後臺的Activity由於記憶體不足,被回收),導致Activity重走生命週期
        * 2.但是FragmentManager會儲存之前的Fragment,當頁面恢復時,會把這些Fragment都顯示出來
        * 3.此時,在Activity的onCreate裡面你再次new Fragment時並且add了一次,會導致Fragment的重疊
        * 4.解決方法是第一次時直接new，第二次頁面恢復後，要使用mFragmentManager通過Tag來取得，
        * 第一次和第二次的判斷標誌就是savedInstanceState是否為null（記憶體回收Activity時，會把資料儲存在savedInstanceState裡）
        * */

//        ★全域性用一個mFragmentManager
        mFragmentManager = getSupportFragmentManager();
        if (savedInstanceState == null) {
            mFragment1 = FragmentFactory.createFragment(F1);
//           ★ 為什麼第一個fragment在新增的時候用的是replace而不是add?
//            防止回退到首頁的時候顯示Activity的空的FrameLayout（這是指有回退棧情況，沒回退棧用add也不會出現空白，因為已經直接退出了）（★★★其實最還是，直接在預設第一個載入的Fragment不要加入回退棧就好了）
            selectFragment1(mFragment1);
        } else {
//            先使用mFragmentManager通過Tag來取得，只要他add過，就給他添加了Tag
//            否則直接重寫建立一個Fragment的話,會導致重疊
            mFragment1 = mFragmentManager.findFragmentByTag(Fragment1.class.getName());
            if (mFragment1 == null) {
                mFragment1 = FragmentFactory.createFragment(FragmentFactory.F1);

            }
            mFragment2 = mFragmentManager.findFragmentByTag(Fragment2.class.getName());
            if (mFragment2 == null) {
//                有可能獲得為空，因為你還沒與把mFragment2新增，還沒有給其設定Tag，所以這裡為空
                mFragment2 = FragmentFactory.createFragment(FragmentFactory.F2);

            }

            mFragment3 = mFragmentManager.findFragmentByTag(Fragment3.class.getName());
            if (mFragment3 == null) {
                mFragment3 = FragmentFactory.createFragment(FragmentFactory.F3);

            }


            position = savedInstanceState.getInt("position");
            switch (position) {
                case 1:
                    selectFragment(mFragment1);
                    break;

                case 2:
                    selectFragment(mFragment2);
                    break;

                case 3:
                    selectFragment(mFragment3);
                    break;
            }

        }

    }


    //記錄Fragment的位置
    private int position = 1;

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        //記錄當前的position
        outState.putInt("position", position);
        Log.e("Ccc", position + "dfssf");
//        ★★★★★★★★別忘了下下面的super.onSave，否則會報錯
        super.onSaveInstanceState(outState);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.tv1:
                if (mFragment1 == null) {
                    mFragment1 = FragmentFactory.createFragment(FragmentFactory.F1);
                }
                selectFragment(mFragment1);
//                    記錄下當前是哪一個Fragment，
//                    方便重新走Activity生命週期時，獲取其死亡時的位置
                position = 1;
                break;

            case R.id.tv2:
                if (mFragment2 == null) {
                    mFragment2 = FragmentFactory.createFragment(FragmentFactory.F2);
                }
                selectFragment(mFragment2);
                position = 2;

                break;

            case R.id.tv3:
                if (mFragment3 == null) {
                    mFragment3 = FragmentFactory.createFragment(FragmentFactory.F3);
                }
                selectFragment(mFragment3);
                position = 3;

                break;
        }
    }

    private void selectFragment(Fragment fragment) {
        FragmentTransaction transaction = mFragmentManager.beginTransaction();
        hideAll(transaction);

        if (!fragment.isAdded()) {
            transaction.add(R.id.fl, fragment, fragment.getClass().getName());
//            transaction.addToBackStack(null);

        }
        Log.e("qqq",mFragmentManager.getBackStackEntryCount()+"qqq");

        transaction.show(fragment).commit();
        Log.e("qqq",mFragmentManager.getBackStackEntryCount()+"hoe");

    }

    private void selectFragment1(Fragment fragment) {
        FragmentTransaction transaction = mFragmentManager.beginTransaction();

            transaction.replace(R.id.fl, fragment, fragment.getClass().getName()).commit();



    }

    private void hideAll(FragmentTransaction transaction) {
        if (mFragment1 != null) {
//            必須使用同一個transaction，跟add/show時候一樣
//            同一個事物進行了所有的add/hide/show，之後統一commit就行了
//            中間不能commit事物，因為一個事物只能是提交一次，重複提交會報錯
//            即：每一次點選，生成一個事物，操作完後，提交這個事物
            transaction.hide(mFragment1);
        }

        if (mFragment2 != null) {
            transaction.hide(mFragment2);
        }

        if (mFragment3 != null) {
            transaction.hide(mFragment3);
        }
    }
    /**
     * 手動回退
     */
    public void popBackStack(){
        if (mFragmentManager.getBackStackEntryCount()>0){
            mFragmentManager.popBackStack();
        }else {
            finish();
        }
    }

    @Override
    public void onBackPressed() {
//        super.onBackPressed();遮蔽掉系統的返回事件
        popBackStack();
    }


}

===

package com.mine.fragmentdemo;

import android.support.v4.app.Fragment;

import java.util.HashMap;

/**
 * Created by a on 2017/4/5.
 */
public class FragmentFactory {
    public final static int F1 = 1;
    public final static int F2 = 2;
    public final static int F3 = 3;

    private static HashMap<Integer, Fragment> mFragments = new HashMap<>();


    public static Fragment createFragment(int fragmentName) {
        // 從快取中取出
        Fragment fragment = mFragments.get(fragmentName);
        if (fragment == null) {
            switch (fragmentName) {

                case F1:
                    fragment = new Fragment1();
                    break;

                case F2:
                    fragment = new Fragment2();

                    break;

                case F3:
                    fragment = new Fragment3();

                    break;
            }
            // 把frament加入到快取中
            mFragments.put(fragmentName,fragment);
        }

        return fragment;
    }
}