Android的碎片popFromBackstack（）只能使用一次 [英] Android Fragment popFromBackstack() only works once

问题描述

我已经得到了我初始化，并承诺像这样两个片段....

I've got two fragments that I am initializing, and committing like so....

碎裂

    getFragmentManager().beginTransaction()
            .add(R.id.filter_fragment, fragmentA)
            .commit();

FragmentB

FragmentB

    getFragmentManager().beginTransaction()
            .replace(R.id.filter_fragment, fragmentB)
            .addToBackStack(null)
            .commit();

碎裂创建并在应用程序启动示出，但没有示出FragmentB直到一个按钮被用户点击

FragmentA is created and shown on application start, but FragmentB is not shown until a button is clicked by the user.

这是我遇到的问题是这样的...

The issue that I am having is this...

1. 片段A在应用程序启动加载


2. 用户操作创建片段B;成功显示片段B。


3. 用户presses设备后退按钮和 getFragmentManager.popBackStack（）被调用。片段显示成功。


4. 用户操作再创片段B;成功显示片段B。



5. 用户presses设备后退按钮和 getFragmentManager.popBackStack（）被调用。并出现以下错误的应用程序崩溃：

1. Fragment A loaded at application start
2. User action creates Fragment B; Fragment B shown successfully.
3. User presses device back button, and getFragmentManager.popBackStack() is called. Fragment A shown successfully.
4. User action creates Fragment B again; Fragment B shown successfully.

5. User presses device back button, and getFragmentManager.popBackStack() is called. Application crash with the following error:

java.lang.IllegalStateException: Fragment already added: FragmentB{3c73b216 #2 id=0x7f0f00c6}

我一直在拉我的头发最后一天试图找出为什么交易和持久性有机污染物backstack工作有一段时间，但坠毁的第二次。我试着玩弄）的，各种组合添加（替换（），删除（）等，它只会变得更糟。我现在崩溃的实现是我得到的最接近。

I've been pulling my hair out for the last day trying to figure out why the transactions and backstack pops work one time, but crash the second time. I've tried playing around with various combinations of add(), replace(), remove(), etc, and it only gets worse. My current crashing implementation is the closest I have gotten.

推荐答案

设置第一个片段：

if (null == savedInstanceState) {
    getSupportFragmentManager().beginTransaction().addToBackStack("fragmentA").replace(R.id.container, new FragmentA(), "CURRENT_FRAGMENT_TAG").commit();
}

在的OnCreate 在活动

---

使用此功能，以取代片段，以避免过度增加同一个数据段又一遍堆栈：

Use this function to replace fragments to avoid adding same fragment over and over again to stack:

public void replaceFragment(Fragment fragment, String tag) {
    Fragment currentFragment = getSupportFragmentManager().findFragmentByTag("CURRENT_FRAGMENT_TAG");

    //to avoid adding the same fragment, you can use 'instanceof' instead of comparator
    if (currentFragment.getClass() == fragment.getClass()) {
        return;
    }
    getSupportFragmentManager().popBackStack(tag, FragmentManager.POP_BACK_STACK_INCLUSIVE);
    getSupportFragmentManager()
            .beginTransaction()
            .addToBackStack(tag).replace(R.id.container, fragment, "CURRENT_FRAGMENT_TAG")
            .commit();

}

执行示例：

replaceFragment(new FragmentB(), "fragmentB");

---

覆盖 onBack pressed 。

@Override
public void onBackPressed() {
    if (getSupportFragmentManager().getBackStackEntryCount() == 1) {
        finish();
    } else {
        super.onBackPressed();
    }
}

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