getIntent() 返回 null

huangapple
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英文:

getIntent() returning null

问题

Here's the translated content:

  1. 我一直在尝试从片段（CrimeFragment）中使用startActivityForResult(Intent，requestCode)启动活动（NewDateActivity）。在CrimeFragment中，它在Date按钮的onClickListener上调用。单击时应用程序崩溃了。也许我在某个地方做了一些愚蠢的事情，但是这是堆栈跟踪-
  3. 2020-07-25 20:35:15.750 19741-19741/com.bignerdranch.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
  4. Process: com.bignerdranch.criminalintent, PID: 19741
  5. java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.bignerdranch.criminalintent/com.bignerdranch.criminalintent.NewDateActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.Serializable android.content.Intent.getSerializableExtra(java.lang.String)' on a null object reference
  6. ...
  8. 以下是CrimeFragment的代码-
  10. ...
  12. 这是活动的代码-
  14. ...
  16. 在解决了上述问题后，我遇到了这个问题-
  18. ...
  20. NewDaPiFragment的代码-
  22. ...

请注意，我已经按照你的要求只返回了翻译好的代码部分，不包含额外的内容。如果你有任何进一步的问题，请随时提问。

英文:

I have been trying to start an Activity(NewDateActivity) from a fragment (CrimeFragment) with startActivityForResult(Intent, requestCode). Its called on Date buttons onClickListener in CrimeFragment. OnClick crashes the app. Maybe am doing something silly somewhere but here's the stack trace-

  1. **2020-07-25 20:35:15.750 19741-19741/com.bignerdranch.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
  2.     Process: com.bignerdranch.criminalintent, PID: 19741
  3.     java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.bignerdranch.criminalintent/com.bignerdranch.criminalintent.NewDateActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.Serializable android.content.Intent.getSerializableExtra(java.lang.String)' on a null object reference
  4.         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
  5.         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
  6.         at android.app.ActivityThread.-wrap14(ActivityThread.java)
  7.         at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
  8.         at android.os.Handler.dispatchMessage(Handler.java)
  9.         at android.os.Looper.loop(Looper.java)
  10.         at android.app.ActivityThread.main(ActivityThread.java)
  11.         at java.lang.reflect.Method.invoke(Native Method)
  12.         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
  13.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
  14.      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.Serializable android.content.Intent.getSerializableExtra(java.lang.String)' on a null object reference
  15.         at com.bignerdranch.criminalintent.NewDateActivity.<init>(NewDateActivity.java:16)
  16.         at java.lang.Class.newInstance(Native Method)
  17.         at android.app.Instrumentation.newActivity(Instrumentation.java)
  18.         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java) 
  19.         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java) 
  20.         at android.app.ActivityThread.-wrap14(ActivityThread.java) 
  21.         at android.app.ActivityThread$H.handleMessage(ActivityThread.java) 
  22.         at android.os.Handler.dispatchMessage(Handler.java) 
  23.         at android.os.Looper.loop(Looper.java) 
  24.         at android.app.ActivityThread.main(ActivityThread.java) 
  25.         at java.lang.reflect.Method.invoke(Native Method) 
  26.         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java) 
  27.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)**

heres my code for CrimeFragment-

  3. import android.app.Activity;
  4. import android.content.Intent;
  5. import android.os.Bundle;
  6. import android.text.Editable;
  7. import android.text.TextWatcher;
  8. import android.view.LayoutInflater;
  9. import android.view.View;
  10. import android.view.ViewGroup;
  11. import android.widget.Button;
  12. import android.widget.CheckBox;
  13. import android.widget.CompoundButton;
  14. import android.widget.EditText;
  16. import androidx.annotation.NonNull;
  17. import androidx.annotation.Nullable;
  18. import androidx.fragment.app.Fragment;
  19. import androidx.fragment.app.FragmentManager;
  21. import java.util.Date;
  22. import java.util.UUID;
  24. public class CrimeFragment extends Fragment {
  25. private Crime mCrime;
  26. private EditText mTitleField;
  27. private Button mDateButton;
  28. private CheckBox mSolvedCheckBox;
  29. private Button mLastButton;
  30. private Button mFirstButton;
  31. public static final String ARGS_CRIME_ID = "crime id bruh";
  32.     private static final String DIALOG_DATE="dialogdate";
  33.     private static final int REQUEST_DATE=0;
  34.     private Button mTimeButton;
  35.     private  String TIME_TAG="tag for showing timefragment";
  36.     private static final int REQUEST_TIME=1;
  38.     @Override
  39.     public void onCreate(@Nullable Bundle savedInstanceState) {
  40.         super.onCreate(savedInstanceState);
  42.         UUID position=(UUID) getArguments().getSerializable(ARGS_CRIME_ID);
  43.    mCrime=CrimeLab.get(getActivity()).getCrime(position);
  44.     }
  46.     @Nullable
  47.     @Override
  48.     public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
  49.         View v=inflater.inflate(R.layout.fragment_crime, container, false);
  52.         mSolvedCheckBox=(CheckBox) v.findViewById(R.id.crime_solved);
  53. mSolvedCheckBox.setChecked(mCrime.isSolved());
  54. mSolvedCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
  55.     @Override
  56.     public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
  57.         mCrime.setSolved(isChecked);
  58.     }
  59. });
  63. mFirstButton=(Button) v.findViewById(R.id.first_button);
  64.         mLastButton=(Button) v.findViewById(R.id.last_button);
  65.         if (CrimePagerActivity.mViewPager.getCurrentItem()==0){
  66.             mFirstButton.setEnabled(false);
  67.         } else if (CrimePagerActivity.mViewPager.getCurrentItem()==99){
  68.             mLastButton.setEnabled(false);
  69.         }
  70. mFirstButton.setOnClickListener(new View.OnClickListener() {
  71.     @Override
  72.     public void onClick(View v) {
  73. CrimePagerActivity.jumpToFirst();
  74.     }
  75. });
  77. mLastButton.setOnClickListener(new View.OnClickListener() {
  78.     @Override
  79.     public void onClick(View v) {
  80. CrimePagerActivity.jumpToLast();
  81.     }
  82. });
  85.        mTitleField=(EditText) v.findViewById(R.id.crime_title);
  86.        mTitleField.setText(mCrime.getTitle());
  87.        mDateButton=(Button) v.findViewById(R.id.crime_date);
  88.         updateDate();
  89.         mDateButton.setOnClickListener(new View.OnClickListener(){
  90.            @Override
  91.            public void onClick(View v){
  92.              Intent data= NewDateActivity.newIntent(getActivity(), mCrime.getDate());
  93.            startActivityForResult(data, REQUEST_DATE);
  94.            }
  95.        });
  97.         mTimeButton=(Button) v.findViewById(R.id.time_button);
  98.         mTimeButton.setOnClickListener(new View.OnClickListener() {
  99.             @Override
  100.             public void onClick(View v) {
  101.                 FragmentManager manager=getFragmentManager();
  102.                 TimePickerFragment fragment= new TimePickerFragment();
  103.                 fragment.show(manager, TIME_TAG);
  104.             }
  105.         });
  107.        mTitleField.addTextChangedListener(new TextWatcher() {
  108.            @Override
  109.            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
  111.            }
  113.            @Override
  114.            public void onTextChanged(CharSequence s, int start, int before, int count) {
  115. mCrime.setTitle(s.toString());
  116.            }
  118.            @Override
  119.            public void afterTextChanged(Editable s) {
  121.            }
  122.        });
  124.         return v;
  126.     }
  128.     @Override
  129.     public void onActivityResult(int requestCode, int resultCode, Intent data){
  130.         if(resultCode!= Activity.RESULT_OK){
  131.             return;
  132.         }
  134.         if (requestCode==REQUEST_DATE){
  135.             Date date=(Date) data.getSerializableExtra(NewDaPiFragment.KEY_FOR_DATE2);
  136.             mCrime.setDate(date);
  137.             updateDate();
  138.         }
  139. if (requestCode==REQUEST_TIME){
  140.     String hour=String.valueOf(data.getIntExtra(TimePickerFragment.HOUR_KEY, 0));
  141.     String minutes=String.valueOf(data.getIntExtra(TimePickerFragment.Minute_KEY, 0));
  142.     String time=hour+ ":"+ minutes;
  143. }
  144.     }
  146.     private void updateDate() {
  147.         mDateButton.setText(mCrime.getDate().toString());
  148.     }
  151.     public static CrimeFragment newInstance( UUID position){
  152.         Bundle args= new Bundle();
  153.         args.putSerializable(ARGS_CRIME_ID, position);
  154.         CrimeFragment fragment= new CrimeFragment();
  155.         fragment.setArguments(args);
  156.         return fragment;
  158. }
  160. }

And my code for the activity-

  1. package com.bignerdranch.criminalintent;
  3. import androidx.appcompat.app.AppCompatActivity;
  4. import androidx.fragment.app.Fragment;
  6. import android.app.Activity;
  7. import android.content.Context;
  8. import android.content.Intent;
  9. import android.os.Bundle;
  11. import java.util.Date;
  13. public class NewDateActivity extends SingleFragmentActivity {
  15.     private static final String KEY="a string key for extracting date";
  18. **public Date date=(Date) getIntent().getSerializableExtra(KEY);
  22. public static Intent newIntent(Context packageContext, Date date){
  23.     Intent intent=new Intent(packageContext, NewDateActivity.class );
  24.     intent.putExtra(KEY, date);
  25.     return intent;
  26. }
  28.     @Override
  29.     protected Fragment createFragment() {
  30.         return NewDaPiFragment.newInstance(date);
  31.     }
  32. }

Am getting this problem after solving the problem above-

  1. 2020-07-26 11:42:36.677 17763-17763/com.bignerdranch.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
  2.     Process: com.bignerdranch.criminalintent, PID: 17763
  3.     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bignerdranch.criminalintent/com.bignerdranch.criminalintent.NewDateActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference
  4.         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
  5.         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
  6.         at android.app.ActivityThread.-wrap14(ActivityThread.java)
  7.         at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
  8.         at android.os.Handler.dispatchMessage(Handler.java)
  9.         at android.os.Looper.loop(Looper.java)
  10.         at android.app.ActivityThread.main(ActivityThread.java)
  11.         at java.lang.reflect.Method.invoke(Native Method)
  12.         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
  13.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
  14.      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference
  15.         at java.util.Calendar.setTime(Calendar.java)
  16.         at com.bignerdranch.criminalintent.NewDaPiFragment.onViewCreated(NewDaPiFragment.java:42)
  17.         at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:892)
  18.         at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
  19.         at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
  20.         at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
  21.         at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
  22.         at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
  23.         at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
  24.         at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
  25.         at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2663)
  26.         at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManagerImpl.java:2613)
  27.         at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:246)
  28.         at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:542)
  29.         at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:201)
  30.         at android.app.Instrumentation.callActivityOnStart(Instrumentation.java)
  31.         at android.app.Activity.performStart(Activity.java)
  32.         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java) 
  33.         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java) 
  34.         at android.app.ActivityThread.-wrap14(ActivityThread.java) 
  35.         at android.app.ActivityThread$H.handleMessage(ActivityThread.java) 
  36.         at android.os.Handler.dispatchMessage(Handler.java) 
  37.         at android.os.Looper.loop(Looper.java) 
  38.         at android.app.ActivityThread.main(ActivityThread.java) 
  39.         at java.lang.reflect.Method.invoke(Native Method) 
  40.         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java) 
  41.         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)

Code for NewDaPiFragment-

  1. package com.bignerdranch.criminalintent;
  3. import android.app.Activity;
  4. import android.content.Intent;
  5. import android.os.Bundle;
  6. import android.view.LayoutInflater;
  7. import android.view.View;
  8. import android.view.ViewGroup;
  9. import android.widget.Button;
  10. import android.widget.DatePicker;
  12. import androidx.annotation.NonNull;
  13. import androidx.annotation.Nullable;
  14. import androidx.fragment.app.Fragment;
  16. import java.util.Calendar;
  17. import java.util.Date;
  18. import java.util.GregorianCalendar;
  20. public class NewDaPiFragment extends Fragment {
  21. private DatePicker mDatePicker;
  22. private Button mOkButton;
  23. public static final String KEY_FOR_DATE="a key that will be used for dates";
  24. public static final String KEY_FOR_DATE2="another key for dates";
  26.     @Nullable
  27.     @Override
  28.     public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
  29.         View v= inflater.inflate(R.layout.dialog_date, container, false);
  30.         return v;
  31.     }
  33.     @Override
  34.     public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
  35.         super.onViewCreated(view, savedInstanceState);
  36.         View v=view;
  37.         
  38.         mDatePicker=(DatePicker) v.findViewById(R.id.dialog_date_picker);
  39.         mOkButton=(Button) v.findViewById(R.id.positive_buttton);
  40.         Date date=(Date) getArguments().getSerializable(KEY_FOR_DATE);
  41.         Calendar calendar=Calendar.getInstance();
  42.         calendar.setTime(date);
  43.         int year =calendar.get(Calendar.YEAR);
  44.         int month=calendar.get(Calendar.MONTH);
  45.         int day=calendar.get(Calendar.DAY_OF_MONTH);
  46.         mDatePicker.init(year, month,day, null );
  47.         mOkButton.setOnClickListener(new View.OnClickListener(){
  48.             @Override
  49.             public void onClick(View v) {
  50.                 int year=mDatePicker.getYear();
  51.                 int month=mDatePicker.getMonth();
  52.                 int day=mDatePicker.getDayOfMonth();
  53.                 Date date1=new GregorianCalendar(year,month,day).getTime();
  54.                 sendResult(Activity.RESULT_OK, date1);
  55.             }
  56.         });
  57.     }
  59.     public static Fragment newInstance(Date date){
  60.         Bundle args=new Bundle();
  61.         args.putSerializable(KEY_FOR_DATE, date);
  62.         Fragment fragment=new NewDaPiFragment();
  63.         fragment.setArguments(args);
  64.         return fragment;
  65.     }
  66. private void sendResult(int resultCode, Date date){
  67.         Intent data=new Intent();
  68.         data.putExtra(KEY_FOR_DATE2, date);
  69.         getActivity().setResult(resultCode, data);
  70. }
  71. }

答案1

得分: 0

你正在类字段中使用 getIntent()，它尚未初始化，在 onCreate() 之后进行所有特定于 Android 的初始化操作 <br>
如果你想将其作为字段变量使用，可以这样做：

  1. public Date date;
  3. @Override
  4. protected void onCreate(Bundle savedInstanceState) {
  5.     super.onCreate(savedInstanceState);
  6.     setContentView(R.layout.your_layout);
  7.     date = (Date) getIntent().getSerializableExtra(KEY);
  8. }

编辑：

对于你的后续问题：

  1. Date date = (Date) getArguments().getSerializable(KEY_FOR_DATE);

在这里你得到了一个空的日期，检查一下你是否已经正确地发送或获取了它。

英文:

You are using getIntent() in class field, It is not yet initalized, all android specific intializations happen after onCreate() <br>
If you want it as a field variable do something like this

> public Date date;
>
> @Override
> protected void onCreate(Bundle savedInstanceState) {
> super.onCreate(savedInstanceState);
> setContentView(R.layout.your_layout);
> date = (Date) getIntent().getSerializableExtra(KEY);
> }

EDIT:

For your follow up question

  1. Date date=(Date) getArguments().getSerializable(KEY_FOR_DATE);

You are gtting date null here, check if you have sent it/ fetching it correctly

huangapple
  • 本文由 发表于 2020年7月26日 04:03:49
  • 转载请务必保留本文链接：https://java.coder-hub.com/63093030.html
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