android片段来回替换

我只有一项活动：

package com.duandianer.ddr_v2.module.login.activity;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTabHost;
import android.support.v4.app.FragmentTransaction;
import android.util.Log;
import android.widget.TabWidget;

import com.duandianer.ddr_v2.R;
import com.duandianer.ddr_v2.common.activity.BaseActivity;
import com.duandianer.ddr_v2.common.fragment.BaseFragment;
import com.duandianer.ddr_v2.module.login.fragment.FindPasswdFragment;
import com.duandianer.ddr_v2.module.login.fragment.LoginFragment;

public class LoginActivity extends BaseActivity {
    private static int FRAGMENT_ID = R.id.login_view_bottom_fragment;
    private FragmentManager mFragmentManager;
    private FragmentTransaction mFragmentTransaction;

    @Override

    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.login_view);
        setFullscreen();

        mFragmentManager = getSupportFragmentManager();
        replaceFragment(LoginFragment.class);
    }


    public void replaceFragment(Class<? extends BaseFragment> C) {
        mFragmentTransaction = mFragmentManager.beginTransaction();
        Fragment old = mFragmentManager.findFragmentById(FRAGMENT_ID);
        Log.d("ddr", old + "");
        try {
            if (old == null)
                mFragmentTransaction.add(FRAGMENT_ID, C.newInstance());
            else if (!C.isInstance(old)) {
                mFragmentTransaction.replace(FRAGMENT_ID, C.newInstance());
            }
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        mFragmentTransaction.commit();
    }
}

package com.duandianer.ddr_v2.module.login.activity；
导入android.os.Bundle；
导入android.support.annotation.Nullable；
导入android.support.v4.app.Fragment；
导入android.support.v4.app.FragmentManager；
导入android.support.v4.app.FragmentTabHost；
导入android.support.v4.app.FragmentTransaction；
导入android.util.Log；
导入android.widget.TabWidget；
导入com.duandianer.ddr_v2.R；
导入com.duandianer.ddr_v2.common.activity.BaseActivity；
导入com.duandianer.ddr_v2.common.fragment.BaseFragment；
导入com.duandianer.ddr_v2.module.login.fragment.FindPasswdFragment；
导入com.duandianer.ddr_v2.module.login.fragment.LoginFragment；
公共类LoginActivity扩展了BaseActivity{
私有静态int FRAGMENT\u ID=R.ID.login\u view\u bottom\u FRAGMENT；
私人碎片管理器MFFragmentManager；
私人碎片交易；
@凌驾
创建时受保护的void（@Nullable Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.login\u视图）；
设置全屏（）；
MFFragmentManager=getSupportFragmentManager（）；
replaceFragment（LoginFragment.class）；
}
public void replaceFragment（类尝试替换登录片段：

mAdapter = new ViewPagerAdapter(getActivity().getSupportFragmentManager());

与

getChildFragmentManager（）应用于处理片段内部的片段。
getChildFragmentManager（）是片段内部使用的片段管理器。getFragmentManager（）或getSupportFragmentManager（）是在活动中使用。要查看关于此的完整解释，您可以查看以下答案：或访问官方android文档关于片段：-。希望对您有所帮助！
package com.duandianer.ddr_v2.module.login.fragment;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.FragmentTabHost;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TabHost;
import android.widget.TabWidget;

import com.duandianer.ddr_v2.R;
import com.duandianer.ddr_v2.common.fragment.BaseFragment;

import java.lang.ref.SoftReference;
import java.util.ArrayList;

public class LoginFragment extends BaseFragment {
    private final ArrayList<Fragment> Fragments = new ArrayList<>();
    private final ArrayList<CharSequence> Titles = new ArrayList<>();
    private SoftReference<View> mView;

    private TabLayout mTabLayout;
    private ViewPager mViewPager;

    private ViewPagerAdapter mAdapter;

    private final LoginFragment_LoginFragment loginFragment_loginFragment =
            new LoginFragment_LoginFragment();

    private final LoginFragment_RegisterFragment loginFragment_registerFragment =
            new LoginFragment_RegisterFragment();

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        if (mView == null || mView.get() == null) {
            View view = inflater.inflate(R.layout.login_view_login_fragment, null);
            mView = new SoftReference<>(view);

            mAdapter = new ViewPagerAdapter(getActivity().getSupportFragmentManager());

            Fragments.add(loginFragment_loginFragment);
            Fragments.add(loginFragment_registerFragment);

            Titles.add("登录");
            Titles.add("注册");

            mTabLayout = (TabLayout) mView.get().findViewById(R.id.login_view_bottom_fragment_tab);
            mViewPager = (ViewPager) mView.get().findViewById(R.id.login_view_bottom_fragment_viewpager);

            mTabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

            mViewPager.setAdapter(mAdapter);

            mTabLayout.setupWithViewPager(mViewPager);

            Log.d("ddr", "create login");
        }

        ViewGroup parent = (ViewGroup) mView.get().getParent();
        if (parent != null)
            parent.removeView(mView.get());
        return mView.get();
    }


    @Override
    public void onDestroy() {
        super.onDestroy();
        mView = null;
        mTabLayout = null;
        mViewPager = null;

        Log.d("ddr", "destroy login");
    }

    private class ViewPagerAdapter extends FragmentPagerAdapter {
        public ViewPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            return Fragments.get(position);
        }

        @Override
        public int getCount() {
            return Fragments.size();
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return Titles.get(position);
        }
    }
}

package com.duandianer.ddr_v2.module.login.fragment;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

import com.duandianer.ddr_v2.R;
import com.duandianer.ddr_v2.common.fragment.BaseFragment;
import com.duandianer.ddr_v2.module.login.activity.LoginActivity;
import com.duandianer.ddr_v2.module.login.controllers.LoginController;

import java.lang.ref.SoftReference;

public class FindPasswdFragment extends BaseFragment {
    private SoftReference<View> mView;

    private LoginController mController;

    private Button mReturn;

    private final OnClickListenerImpl onClickListener = new OnClickListenerImpl();

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        if (mView == null || mView.get() == null) {
            mView = new SoftReference<>(inflater.inflate(R.layout.login_view_find_passwd_fragment, null));

            mReturn = (Button) mView.get().findViewById(R.id.login_view_bottom_fragment_find_passwd_button_return);
            mReturn.setOnClickListener(onClickListener);

            mController = LoginController.SingTon.INSTANCE.getInstance((LoginActivity) getActivity());
        }
        ViewGroup parent = (ViewGroup) mView.get().getParent();
        if (parent != null)
            parent.removeView(mView.get());
        return mView.get();
    }

    private class OnClickListenerImpl implements View.OnClickListener {
        @Override
        public void onClick(View v) {
            if (v == mReturn) {
                mController.replaceFragment(LoginFragment.class);
            }
        }
    }
}

mAdapter = new ViewPagerAdapter(getActivity().getSupportFragmentManager());

mAdapter = new ViewPagerAdapter(getChildFragmentManager());