Question

我有一个Activity，其中有一个PlaceholderFragment子类。我正在尝试将int传递到PlaceholderFragment（显然可以，我返回了int并将其打印到logcat，这确实是正确的），但是当{ {1}}方法运行后，通过的onCreateView()突然消失并重置为0。我在做什么错了？

这是我的int中负责传递Activity的代码：

int

以下是public void setActivityTitle(){ toolbar = findViewById(R.id.toolbar); resName = getIntent().getExtras().getString("Name"); this.ResID = getIntent().getExtras().getInt("ResID"); PlaceholderFragment pf = new PlaceholderFragment(ResID); //↑ I know that PlaceholderFragments should almost always have default constructors, but I was desperate. The default empty constructor is still there though pf.receiveResID(ResID); //↑ This method is basically a setter for the ResID int Log.e("SplitBill","ResID that we got from PlaceholderFragment is " + pf.getResID()); //↑ This output is as expected, and matches the int that I pass down toolbar.setTitle(resName); }中int的相关声明字段，构造函数和getter / setter：

PlaceholderFragment

这是我的private int ResID; public PlaceholderFragment() { } public PlaceholderFragment(int resID) { this.ResID = resID; Log.e("SplitBill","PlaceholderFragment: Received ResID as " + ResID); //↑ This returns the correct int to logcat } public int getResID() { return ResID; //Outside the subclass, this returns the correct int. Inside it, this returns 0 } public void receiveResID(int ResID) { this.ResID = ResID; Log.e("SplitBill","PlaceholderFragment: Received ResID as " + ResID); //↑ This also works as expected }的一部分，应该在数据库查询中使用onCreaeView()：

int

编辑：@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { final View rootView = inflater.inflate(R.layout.fragment_menu, container, false); MenuViewModel viewModel = ViewModelProviders.of(this).get(MenuViewModel.class); //MenuActivity m = new MenuActivity(); //int resID = m.getResID(); //↑ This was my attempt at trying to get the int straight from a getter in the MenuActivity, it returns 0 Log.e("SplitBill","From onCreateView(): ResID is " + ResID); //↑ This also prints 0 to logcat viewModel.setResID(ResID);是MenuActivity中的另一个子类。它负责获取SectionsPagerAdapter的实例。这是全部内容：

PlaceholderFragment

Answer 1

您只能将空构造函数与Fragments一起使用。

public static MyFragment newInstance(int someInt) {
    MyFragment myFragment = new MyFragment();

    Bundle args = new Bundle();
    args.putInt("someInt", someInt);
    myFragment.setArguments(args);

    return myFragment;
}

MyFragment fragment = MyFragment.newInstance(5);是获取片段实例并设置值的方式。

要获取价值，请使用getArguments().getInt("someInt", 0);片段方法内的onCreate()

如何在子类中使用主类中的子类中的变量集？

1 个答案: