Java 如何在父片段而不是父活动中正确获取DatePicker值
我有一个复杂的应用程序,有大量的片段和子片段,我需要侦听器在片段中侦听,而不是在活动中侦听。这通常有效,但不适用于日期或时间选择器 下面是一个示例应用程序,其中包含一个膨胀的片段-TestFragmentMain。这个膨胀的片段还有两个片段——一个带有单个EditText(TestFragment\u InputBox),另一个带有单个TextView(TestFragment\u DateBox),用于侦听事件(TextChangeListener和DateChangeListener) 关于文本变化的第一个片段,所有作品都像一个符咒,主要片段是接受结果 但是,在日期更改时,我收到并出错:Java 如何在父片段而不是父活动中正确获取DatePicker值,java,android,android-fragments,android-datepicker,Java,Android,Android Fragments,Android Datepicker,我有一个复杂的应用程序,有大量的片段和子片段,我需要侦听器在片段中侦听,而不是在活动中侦听。这通常有效,但不适用于日期或时间选择器 下面是一个示例应用程序,其中包含一个膨胀的片段-TestFragmentMain。这个膨胀的片段还有两个片段——一个带有单个EditText(TestFragment\u InputBox),另一个带有单个TextView(TestFragment\u DateBox),用于侦听事件(TextChangeListener和DateChangeListener) 关于
java.lang.NullPointerException: Attempt to invoke interface method 'void com.gmail.xxx.xxx.test.DateChangeListener.dateChanged(int, int, int)' on a null object reference
at com.gmail.xxx.xxx.test.TestFragment_DatePicker.onDateSet(TestFragment_DatePicker.java:32)
我真的不明白为什么。感谢您的帮助
主要活动:
public class TestClass extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.test_activity);
TestFragmentMain testFragmentMain = new TestFragmentMain();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.test_fragment_container, testFragmentMain);
ft.commitAllowingStateLoss();
}
}
主片段,带侦听器
public class TestFragmentMain extends Fragment implements TextChangeListener, DateChangeListener {
@Override
public View onCreateView(@NotNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.test_fragment, container, false);
TestFragment_InputBox testFragmentInputBox = new TestFragment_InputBox();
FragmentTransaction ft = getChildFragmentManager().beginTransaction();
ft.replace(R.id.test_fragment_inputbox_container, testFragmentInputBox);
ft.commitAllowingStateLoss();
TestFragment_DateBox testFragmentDateBox = new TestFragment_DateBox();
ft = getChildFragmentManager().beginTransaction();
ft.replace(R.id.test_fragment_date_container, testFragmentDateBox);
ft.commitAllowingStateLoss();
return view;
}
@Override
public void onAttach(@NotNull Context context) {
super.onAttach(context);
}
@Override
public void textChanged() {
Log.d("LISTEN","Text has been changed...");
}
@Override
public void dateChanged(int year, int month, int day) {
Log.d("LISTEN","Date has been changed to ...");
}
}
带有输入框的片段:
public class TestFragment_InputBox extends Fragment {
private TextChangeListener textChangeListener;
@Override
public View onCreateView(@NotNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.test_input_box, container, false);
EditText editText = view.findViewById(R.id.input_view);
editText.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
}
@Override
public void afterTextChanged(Editable s) {
textChangeListener.textChanged();
}
});
return view;
}
@Override
public void onAttach(@NotNull Context context) {
super.onAttach(context);
try {
textChangeListener = (TextChangeListener) getParentFragment();
} catch (ClassCastException e) {
e.printStackTrace();
}
}
}
带有日期框的片段:
public class TestFragment_DateBox extends Fragment implements DateChangeListener {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.test_date_box, container, false);
TextView textView = view.findViewById(R.id.date_view);
textView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
DialogFragment datePicker = new TestFragment_DatePicker();
datePicker.show(getActivity().getSupportFragmentManager(), "datePicker");
}
});
return view;
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
}
@Override
public void dateChanged(int year, int month, int day) {
Log.d("LISTEN","Date has been changed in box fragment with box ...");
}
}
日期选择器片段
public class TestFragment_DatePicker extends DialogFragment implements DatePickerDialog.OnDateSetListener {
public DateChangeListener dateChangeListener;
@NotNull
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
final Calendar c = Calendar.getInstance();
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int day = c.get(Calendar.DAY_OF_MONTH);
return new DatePickerDialog(Objects.requireNonNull(getContext()), this, year, month, day);
}
@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
dateChangeListener.dateChanged(year,month,day);
}
@Override
public void onAttach(@NotNull Context context) {
super.onAttach(context);
try {
dateChangeListener = (DateChangeListener) getParentFragment();
} catch (ClassCastException e) {
e.printStackTrace();
}
}
}
和听众:
public interface TextChangeListener {
void textChanged();
}
public interface DateChangeListener {
void dateChanged(int year,int month,int day);
}
问题在于,您没有膨胀
TestFragment\u DatePicker
这是一个DialogFragment
这是一个Fragment
,而是返回一个DatePickerDialog
这是一个AlertDialog
这是一个没有mParentFragment
的对话框。这就是为什么getParentFragment()
返回null
这看起来像是一个糟糕的架构设计,我们继承了旧版本的android。我找到了一个解决方案
在TestFragmentMain中,TestFragment_DateBox需要使用与DatePicker相同的FragmentManager进行处理。这是TestFragmentMain中的代码:
TestFragment_DateBox testFragmentDateBox = new TestFragment_DateBox();
FragmentTransaction ft2 = this.getChildFragmentManager().beginTransaction();
ft2.replace(R.id.test_fragment_date_container, testFragmentDateBox);
ft2.commitAllowingStateLoss();
打开DatePicker时,TestFragment_DateBox中也会发生更改:
DialogFragment datePicker = new TestFragment_DatePicker();
datePicker.setTargetFragment(this, 0);
datePicker.show(this.getFragmentManager(), "datePicker");
我们需要运行setTargetFragment才能工作
现在,该测试开始工作。您的片段TestFragment\u DateBox
调用日期选择器并继承DatePickerDialog.OnDateSetListener
public class TestFragment_DateBox extends Fragment implements DatePickerDialog.OnDateSetListener
然后像这样显示日期选择器片段
TestFragment_DatePicker().show(this.childFragmentManager, "datepicker")
和覆盖onDateSet
@Override
public void onDateSet(DatePicker view, int year, int month, int day) {
// As you are in the calling fragment you can use the values as you see fit
TextView textView = view.findViewById(R.id.date_view);
textView.text = year.toString()
}
在TestFragment\u DatePicker
中有一个侦听器
private lateinit var listener: DatePickerDialog.OnDateSetListener
然后超越转速计
override fun onAttach(context: Context) {
super.onAttach(context)
// Verify that the dialog parent implements the callback interface
try {
// Instantiate the OnDateSetListener so we can send events to the host
listener = parentFragment as DatePickerDialog.OnDateSetListener
} catch (e: ClassCastException) {
// The parent doesn't implement the interface, throw exception
throw ClassCastException(("$context must implement OnDateSetListener"))
}
}
为java和kotlin的混合表示歉意,但你明白了 检查你的日志。当附加TestFragment\u DatePicker时,您没有看到ClassCastException。。。它是空的。只是不知道为什么那个监听器是空的,而另一个不是空的并且正在工作。好的。很明显,DI已经尝试在其父片段(TestFragment_DateBox)以及父片段(TestFragmentMain)中实现侦听器,并且在两者中都实现了侦听器。。。未工作。看起来DialogFragment中的getParentFragment()未按预期工作。调用了onAttach,在那里我看到DateChangeListener为null。然而,当我在DatePicker上实际选择日期时调用它,而不是之前它返回null我几乎可以肯定这是因为你返回的是数据采集器而不是膨胀碎片,但让我完成我的调查:D