Android使得Fragment 切換時不從新實例化

之前實現Fragment的切換都是用replace方法實現

public void startFragmentAdd(Fragment fragment) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.main_layout, fragment, fragment.getClass().getName())
        .commit();
}

 replace()方法只是在上一個Fragment再也不須要時採用的簡便方法。所以，每次切換的時候，Fragment都會從新實例化，從新加載數據。

若是要實現Fragment 切換時不從新實例化，正確的切換方式是add()，切換時hide()當前，add()另外一個Fragment；再次切換時，只需hide()當前，show()另外一個。

// fragment的切換
private void startFragmentAdd(Fragment fragment) {
    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager
         .beginTransaction();
    if (current_fragment == null) {
        fragmentTransaction.add(R.id.main_layout, fragment).commit();
        current_fragment = fragment;
    }
    if (current_fragment != fragment) {
        // 先判斷是否被add過
        if (!fragment.isAdded()) {
            // 隱藏當前的fragment，add下一個到Activity中
            fragmentTransaction.hide(current_fragment)
                  .add(R.id.main_layout, fragment).commit();
        } else {
            // 隱藏當前的fragment，顯示下一個
            fragmentTransaction.hide(current_fragment).show(fragment)
                  .commit();
        }
        current_fragment = fragment;
    }
}