Android - 如何阻止片段自动恢复其状态？

Question

我创建了一个全新的项目来演示我的问题。基本上，我的片段有两个RadioButton. 当 onCreateView 时，我总是使用radioButtonFirst.setChecked(true);. 但是，如果我检查radioButtonSecond然后按“后退”按钮导航，下次打开它时，它会自动检查radioButtonSecond. 这种行为打破了我的逻辑。

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private WeirdFragment weirdFragment;
    private FragmentManager fragmentManager;
    private FragmentTransaction fragmentTransaction;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        weirdFragment = new WeirdFragment();
        fragmentManager = getSupportFragmentManager();
    }
    public void openFragment(View v){
        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.container, weirdFragment);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }
}

奇怪的Fragment.java

public class WeirdFragment extends Fragment {
    private RadioButton radioButtonFirst;
    private RadioButton radioButtonSecond;
    private Button buttonReturn;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_weird, container, false);
        radioButtonFirst = view.findViewById(R.id.radio_button_first);
        radioButtonSecond = view.findViewById(R.id.radio_button_second);
        buttonReturn = view.findViewById(R.id.button_return);

        radioButtonFirst.setChecked(true);

        // I decide to set a listener right here, to see what happened to my radio button. So this listener will be removed in my real project.
        radioButtonSecond.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                Log.v("weird", "i got here");
            }
        });
        buttonReturn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                getFragmentManager().beginTransaction().remove(WeirdFragment.this).commit();
            }
        });
        return view;
    }
}

活动主文件

<Button
    android:id="@+id/button_open"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="openFragment"
    android:text="Open"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<FrameLayout
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintTop_toBottomOf="@id/button_open" />

片段_weird.xml

<RadioGroup
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    app:layout_constraintTop_toTopOf="parent">

    <RadioButton
        android:id="@+id/radio_button_first"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:checked="true"
        android:text="First" />

    <RadioButton
        android:id="@+id/radio_button_second"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Second" />
</RadioGroup>

<Button
    android:id="@+id/button_return"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Return"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintStart_toStartOf="parent" />

我在日志语句处设置了断点。当由用户操作触发该断点时，堆栈跟踪将如下所示：

onCheckedChanged:31, WeirdFragment$1 (com.peanut.myweirdradiobutton)
setChecked:154, CompoundButton (android.widget)
toggle:113, CompoundButton (android.widget)
toggle:78, RadioButton (android.widget)
performClick:118, CompoundButton (android.widget)
run:19866, View$PerformClick (android.view)
handleCallback:739, Handler (android.os)
dispatchMessage:95, Handler (android.os)
loop:135, Looper (android.os)
main:5254, ActivityThread (android.app)
invoke:-1, Method (java.lang.reflect)
invoke:372, Method (java.lang.reflect)
run:903, ZygoteInit$MethodAndArgsCaller (com.android.internal.os)
main:698, ZygoteInit (com.android.internal.os)

但是当断点突然被触发时，stracktrace 看起来像这样：

onCheckedChanged:31, WeirdFragment$1 (com.peanut.myweirdradiobutton)
setChecked:154, CompoundButton (android.widget)
onRestoreInstanceState:522, CompoundButton (android.widget)
dispatchRestoreInstanceState:13740, View (android.view)
dispatchRestoreInstanceState:2893, ViewGroup (android.view)
dispatchRestoreInstanceState:2893, ViewGroup (android.view)
restoreHierarchyState:13718, View (android.view)
restoreViewState:494, Fragment (android.support.v4.app)
moveToState:1486, FragmentManagerImpl (android.support.v4.app)
moveFragmentToExpectedState:1784, FragmentManagerImpl (android.support.v4.app)
moveToState:1852, FragmentManagerImpl (android.support.v4.app)
executeOps:802, BackStackRecord (android.support.v4.app)
executeOps:2625, FragmentManagerImpl (android.support.v4.app)
executeOpsTogether:2411, FragmentManagerImpl (android.support.v4.app)
removeRedundantOperationsAndExecute:2366, FragmentManagerImpl (android.support.v4.app)
execPendingActions:2273, FragmentManagerImpl (android.support.v4.app)
run:733, FragmentManagerImpl$1 (android.support.v4.app)
handleCallback:739, Handler (android.os)
dispatchMessage:95, Handler (android.os)
loop:135, Looper (android.os)
main:5254, ActivityThread (android.app)
invoke:-1, Method (java.lang.reflect)
invoke:372, Method (java.lang.reflect)
run:903, ZygoteInit$MethodAndArgsCaller (com.android.internal.os)
main:698, ZygoteInit (com.android.internal.os)

所以我可以看到它是 onRestoreInstanceState 检查我的radioButtonSecond. 但我不知道如何预防。我正在考虑的事情：

1. 在 onViewStateRestored 中执行我的逻辑。但这是一个不干净的解决方案。
2. 每次我需要打开片段时都重新创建它。但是创建新片段时的初始化阶段成本很高，我不应该这样做。

在我的真实项目中，这个片段就像我的应用程序中某些内容的设置，它有一个“取消”和一个“确定”按钮。所以，我希望片段每次打开时都处于默认状态，因为我认为，例如，用户可能配置很多很多东西，但然后按取消，那么看到所有视图都处于默认状态是合理的状态，而不是配置的状态（也许这种想法导致了我的问题，这是一种良好的用户体验吗？）

那么，如何防止我的片段在未经我许可的情况下恢复其状态呢？

Answer 1

如果我理解正确的话，您希望RadioButton在用户离开之前重置 s 的状态，Fragment以便为Fragment稍后重新进入的情况做好准备。

由于您希望RadioButton每次用户Fragment离开后重新进入时都进行第一个检查，但（我想）不是当用户刚刚离开您的应用程序半小时然后返回到他们离开的地方继续时，您应该使用savingInstanceState Bundle确保RadioButtons 根据情况具有正确的状态：

我们引入一个字段private boolean isFirstButtonChecked = true;。

使用来跟踪sOnCheckedChangeListener的检查状态RadioButton

isFirstButtonChecked = radioButtonFirst.isChecked();

除此之外，boolean将trueOnClickListener

buttonReturn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            isFirstButtonChecked = true;
            getFragmentManager().beginTransaction().remove(WeirdFragment.this).commit();
        }
});

现在您可以将所需的状态保存在onSaveInstanceState()：

     @Override
public void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putBoolean("FIRST_RB_STATE", isFirstButtonChecked);
}

@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
    super.onViewStateRestored(savedInstanceState);
    isFirstButtonChecked = savedInstanceState == null 
            ? true 
            : savedInstanceState.getBoolean("FIRST_RB_STATE");
    radioButtonFirst.setChecked(isFirstButtonChecked);
}

我知道这意味着添加大量代码。但由于你不愿意Fragment每次从头开始重新创建你的，我想它包含的不仅仅是两个RadioButton。因此，让运行时为您工作而不是与之抗争，使这种方法比仅仅调用相应的方法更干净、更安全。super.onViewStateRestored(null);