private void setDefaultFragment() {

    FragmentManager fm = getFragmentManager();
    FragmentTransaction transaction = fm.beginTransaction();
    mFragmentOne = new FragmentOne();
    mFragmentOne.setClickEnable();
    transaction.replace(R.id.frameLayout_content, mFragmentOne);
    transaction.commit();
  }
  /**
   * Fragment常用的三个类
   *
   * <p>android.app.Fragment 主要用于定义Fragment
   *
   * <p>android.app.FragmentManager 主要用于在Activity中操作Fragment
   *
   * <p>android.app.FragmentTransaction 保证一些列Fragment操作的原子性,熟悉事务这个词,一定能明白~
   *
   * @param v
   */
  @Override
  public void onClick(View v) {

    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fgtransaction = fragmentManager.beginTransaction();

    switch (v.getId()) {
      case R.id.btn_one:
        {
          if (mFragmentOne == null) {
            mFragmentOne = new FragmentOne();
            mFragmentOne.setClickEnable();
          }
          fgtransaction.replace(R.id.frameLayout_content, mFragmentOne);
          break;
        }

      case R.id.btn_two:
        {
          if (mFragmentTwo == null) {
            mFragmentTwo = new FragmentTwo();
            mFragmentTwo.setClickEnable();
          }

          fgtransaction.replace(R.id.frameLayout_content, mFragmentTwo);
          break;
        }

        //            case R.id.btn_one: {
        //                if (mFragmentTwo!=null){
        //                    fgtransaction.hide(mFragmentTwo);
        //                }
        //
        //                if (mFragmentOne == null) {
        //                    mFragmentOne = new FragmentOne();
        //                    mFragmentOne.setClickEnable();
        //                    fgtransaction.add(R.id.frameLayout_content, mFragmentOne);
        //                }else{
        //                    fgtransaction.show(mFragmentOne);
        //                }
        //                break;
        //            }
        //
        //            case R.id.btn_two: {
        //
        //                if (mFragmentOne!=null){
        //                    fgtransaction.hide(mFragmentOne);
        //                }
        //
        //                if (mFragmentTwo == null) {
        //                    mFragmentTwo = new FragmentTwo();
        //                    mFragmentTwo.setClickEnable();
        //                    fgtransaction.add(R.id.frameLayout_content,mFragmentTwo);
        //                }else{
        //                    fgtransaction.show(mFragmentTwo);
        //                }
        //                break;
        //            }

      default:
        {
          break;
        }
    }
    fgtransaction.commit();
  }