切換標簽時保持片段狀態

Question

我有4個標簽A，B，C和D。我想保留以前的標簽視圖。 例如：標簽A（默認）-> B->A。返回標簽A時，我希望標簽A的視圖與以前相同

這是我的代碼：

private void replaceFragment(Constants.BottomTab bottomTab) {
    Fragment fragment = getSupportFragmentManager().findFragmentByTag(bottomTab.getValue());
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    if (fragment == null) {
        switch (bottomTab) {
            case A:
                fragment = new A();
                break;
            case B:
                fragment = new B();
                break;
            case C:
                fragment = new C();
                break;
            case D:
                fragment = new D();
                break;
        }
        transaction.replace(R.id.main_container, fragment,bottomTab.getValue() );
        transaction.addToBackStack(bottomTab.getValue()); // Tag
        transaction.commit();
        Log.v(">>>", "Create fragment: " + fragment.getTag());
    } else { // pop from stack
        transaction.replace(R.id.main_container, fragment, bottomTab.getValue());
        transaction.commit();
        Log.v(">>>", "Found fragment: " + fragment.getTag());
    }
}

從選項卡B切換到選項卡A時，它會不斷重新創建

我知道另一種方法是使用ViewPager和ViewPager.setOffscreenPageLimit(4)但是上述代碼的解決方案是什么？

有人可以幫忙嗎？ 提前致謝！

Answer 1

作為一個簡單的解決方案，我建議您保留對這些片段的引用，並僅在它們為null時才創建它們。 因此可能是這樣的：

private Fragment aFrag;
private Fragment bFrag;
private Fragment cFrag;
private Fragment dFrag;

private void replaceFragment(Constants.BottomTab bottomTab) {
    Fragment fragment = getSupportFragmentManager().findFragmentByTag(bottomTab.getValue());
    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    if (fragment == null) {
        switch (bottomTab) {
            case A:
                if (aFrag == null) aFrag = new A();
                fragment = aFrag;
                break;
            case B:
                if (bFrag == null) bFrag = new B();
                fragment = bFrag;
                break;
            case C:
                if (cFrag == null) cFrag = new C();
                fragment = cFrag;
                break;
            case D:
                if (dFrag == null) dFrag = new D();
                fragment = dFrag;
                break;
        }
        transaction.replace(R.id.main_container, fragment,bottomTab.getValue() );
        transaction.addToBackStack(bottomTab.getValue()); // Tag
        transaction.commit();
        Log.v(">>>", "Create fragment: " + fragment.getTag());
    } else { // pop from stack
        transaction.replace(R.id.main_container, fragment, bottomTab.getValue());
        transaction.commit();
        Log.v(">>>", "Found fragment: " + fragment.getTag());
    }
}