假設場景：登入、註冊

MainActivity初始化和監聽返回鍵

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mFragmentManager = getSupportFragmentManager();
        addFragment(new LoginFragment(), "login"
 
);

    }

    public void addFragment(Fragment fragment, String tag) {
        FragmentTransaction beginTransaction = mFragmentManager.beginTransaction();
        beginTransaction.add(R.id.login_content, fragment, tag);
        // 新增到回退棧,並定義標記
        beginTransaction.addToBackStack(tag);
        beginTransaction.commit();
    }

    /**
     * 監聽返回鍵
     */
 

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            // 獲取當前回退棧中的Fragment個數
            int backStackEntryCount = mFragmentManager.getBackStackEntryCount();
            // 回退棧中至少有多個fragment,棧底部是首頁
            if (backStackEntryCount > 1
 
) {
                // 回退一步
                mFragmentManager.popBackStackImmediate();
                // 獲取當前退到了哪一個Fragment上,重新獲取當前的Fragment回退棧中的個數
                FragmentManager.BackStackEntry backStack = mFragmentManager.getBackStackEntryAt(mFragmentManager.getBackStackEntryCount() - 1);
                // 獲取當前棧頂的Fragment的標記值
                String tag = backStack.getName();
                if (tag.equals("login")) {
                    if (isLogin) {
                        addFragment(new LoginFragment(), "login");
                        isLogin = false;
                    } else
                        finish();
                }
            } else {
                finish();
            }
        }
        return true;
    }

LoginFragment中的事件處理

    @OnClick({R.id.btn_register})
    public void onViewClicked(View view) {
        switch (view.getId()) {
            case R.id.btn_register:
                LoginActivity activity = (LoginActivity) getActivity();
                activity.addFragment(new RegisterFragment(), "register");
                FragmentTransaction fragmentTransaction = getActivity().getSupportFragmentManager().beginTransaction();
                fragmentTransaction.hide(getActivity().getSupportFragmentManager().findFragmentByTag("login"));
                fragmentTransaction.commit();
                break;
        }
    }

RegisterFragment中的事件處理

    @OnClick({R.id.btn_back})
    public void onViewClicked(View view) {
        switch (view.getId()) {
            case R.id.btn_back:
                FragmentTransaction fragmentTransaction = getActivity().getSupportFragmentManager().beginTransaction();
                fragmentTransaction.show(getActivity().getSupportFragmentManager().findFragmentByTag("login"));
                fragmentTransaction.hide(getActivity().getSupportFragmentManager().findFragmentByTag("register"));
                fragmentTransaction.commit();
                break;
        }
    }