getIntent() 返回 null

huangapple
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英文:

getIntent() returning null

问题

Here's the translated content:

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-

2020-07-25 20:35:15.750 19741-19741/com.bignerdranch.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.bignerdranch.criminalintent, PID: 19741
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
...

以下是CrimeFragment的代码-

...

这是活动的代码-

...

在解决了上述问题后，我遇到了这个问题-

...

NewDaPiFragment的代码-

...

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-

**2020-07-25 20:35:15.750 19741-19741/com.bignerdranch.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.bignerdranch.criminalintent, PID: 19741
    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
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
        at android.app.ActivityThread.-wrap14(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
        at android.os.Handler.dispatchMessage(Handler.java)
        at android.os.Looper.loop(Looper.java)
        at android.app.ActivityThread.main(ActivityThread.java)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
     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
        at com.bignerdranch.criminalintent.NewDateActivity.<init>(NewDateActivity.java:16)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java) 
        at android.app.ActivityThread.-wrap14(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java) 
        at android.os.Handler.dispatchMessage(Handler.java) 
        at android.os.Looper.loop(Looper.java) 
        at android.app.ActivityThread.main(ActivityThread.java) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)**

heres my code for CrimeFragment-



import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.EditText;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;

import java.util.Date;
import java.util.UUID;

public class CrimeFragment extends Fragment {
private Crime mCrime;
private EditText mTitleField;
private Button mDateButton;
private CheckBox mSolvedCheckBox;
private Button mLastButton;
private Button mFirstButton;
public static final String ARGS_CRIME_ID = "crime id bruh";
    private static final String DIALOG_DATE="dialogdate";
    private static final int REQUEST_DATE=0;
    private Button mTimeButton;
    private  String TIME_TAG="tag for showing timefragment";
    private static final int REQUEST_TIME=1;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        UUID position=(UUID) getArguments().getSerializable(ARGS_CRIME_ID);
   mCrime=CrimeLab.get(getActivity()).getCrime(position);
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v=inflater.inflate(R.layout.fragment_crime, container, false);


        mSolvedCheckBox=(CheckBox) v.findViewById(R.id.crime_solved);
mSolvedCheckBox.setChecked(mCrime.isSolved());
mSolvedCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        mCrime.setSolved(isChecked);
    }
});



mFirstButton=(Button) v.findViewById(R.id.first_button);
        mLastButton=(Button) v.findViewById(R.id.last_button);
        if (CrimePagerActivity.mViewPager.getCurrentItem()==0){
            mFirstButton.setEnabled(false);
        } else if (CrimePagerActivity.mViewPager.getCurrentItem()==99){
            mLastButton.setEnabled(false);
        }
mFirstButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
CrimePagerActivity.jumpToFirst();
    }
});

mLastButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
CrimePagerActivity.jumpToLast();
    }
});


       mTitleField=(EditText) v.findViewById(R.id.crime_title);
       mTitleField.setText(mCrime.getTitle());
       mDateButton=(Button) v.findViewById(R.id.crime_date);
        updateDate();
        mDateButton.setOnClickListener(new View.OnClickListener(){
           @Override
           public void onClick(View v){
             Intent data= NewDateActivity.newIntent(getActivity(), mCrime.getDate());
           startActivityForResult(data, REQUEST_DATE);
           }
       });

        mTimeButton=(Button) v.findViewById(R.id.time_button);
        mTimeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentManager manager=getFragmentManager();
                TimePickerFragment fragment= new TimePickerFragment();
                fragment.show(manager, TIME_TAG);
            }
        });

       mTitleField.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) {
mCrime.setTitle(s.toString());
           }

           @Override
           public void afterTextChanged(Editable s) {

           }
       });

        return v;

    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data){
        if(resultCode!= Activity.RESULT_OK){
            return;
        }

        if (requestCode==REQUEST_DATE){
            Date date=(Date) data.getSerializableExtra(NewDaPiFragment.KEY_FOR_DATE2);
            mCrime.setDate(date);
            updateDate();
        }
if (requestCode==REQUEST_TIME){
    String hour=String.valueOf(data.getIntExtra(TimePickerFragment.HOUR_KEY, 0));
    String minutes=String.valueOf(data.getIntExtra(TimePickerFragment.Minute_KEY, 0));
    String time=hour+ ":"+ minutes;
}
    }

    private void updateDate() {
        mDateButton.setText(mCrime.getDate().toString());
    }


    public static CrimeFragment newInstance( UUID position){
        Bundle args= new Bundle();
        args.putSerializable(ARGS_CRIME_ID, position);
        CrimeFragment fragment= new CrimeFragment();
        fragment.setArguments(args);
        return fragment;

}

}

And my code for the activity-

package com.bignerdranch.criminalintent;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

import java.util.Date;

public class NewDateActivity extends SingleFragmentActivity {

    private static final String KEY="a string key for extracting date";


**public Date date=(Date) getIntent().getSerializableExtra(KEY);



public static Intent newIntent(Context packageContext, Date date){
    Intent intent=new Intent(packageContext, NewDateActivity.class );
    intent.putExtra(KEY, date);
    return intent;
}

    @Override
    protected Fragment createFragment() {
        return NewDaPiFragment.newInstance(date);
    }
}

Am getting this problem after solving the problem above-

2020-07-26 11:42:36.677 17763-17763/com.bignerdranch.criminalintent E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.bignerdranch.criminalintent, PID: 17763
    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
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)
        at android.app.ActivityThread.-wrap14(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
        at android.os.Handler.dispatchMessage(Handler.java)
        at android.os.Looper.loop(Looper.java)
        at android.app.ActivityThread.main(ActivityThread.java)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference
        at java.util.Calendar.setTime(Calendar.java)
        at com.bignerdranch.criminalintent.NewDaPiFragment.onViewCreated(NewDaPiFragment.java:42)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:892)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
        at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727)
        at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2663)
        at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManagerImpl.java:2613)
        at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:246)
        at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:542)
        at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:201)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java)
        at android.app.Activity.performStart(Activity.java)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java) 
        at android.app.ActivityThread.-wrap14(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java) 
        at android.os.Handler.dispatchMessage(Handler.java) 
        at android.os.Looper.loop(Looper.java) 
        at android.app.ActivityThread.main(ActivityThread.java) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)

Code for NewDaPiFragment-

package com.bignerdranch.criminalintent;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.DatePicker;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class NewDaPiFragment extends Fragment {
private DatePicker mDatePicker;
private Button mOkButton;
public static final String KEY_FOR_DATE="a key that will be used for dates";
public static final String KEY_FOR_DATE2="another key for dates";

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v= inflater.inflate(R.layout.dialog_date, container, false);
        return v;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        View v=view;
        
        mDatePicker=(DatePicker) v.findViewById(R.id.dialog_date_picker);
        mOkButton=(Button) v.findViewById(R.id.positive_buttton);
        Date date=(Date) getArguments().getSerializable(KEY_FOR_DATE);
        Calendar calendar=Calendar.getInstance();
        calendar.setTime(date);
        int year =calendar.get(Calendar.YEAR);
        int month=calendar.get(Calendar.MONTH);
        int day=calendar.get(Calendar.DAY_OF_MONTH);
        mDatePicker.init(year, month,day, null );
        mOkButton.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                int year=mDatePicker.getYear();
                int month=mDatePicker.getMonth();
                int day=mDatePicker.getDayOfMonth();
                Date date1=new GregorianCalendar(year,month,day).getTime();
                sendResult(Activity.RESULT_OK, date1);
            }
        });
    }

    public static Fragment newInstance(Date date){
        Bundle args=new Bundle();
        args.putSerializable(KEY_FOR_DATE, date);
        Fragment fragment=new NewDaPiFragment();
        fragment.setArguments(args);
        return fragment;
    }
private void sendResult(int resultCode, Date date){
        Intent data=new Intent();
        data.putExtra(KEY_FOR_DATE2, date);
        getActivity().setResult(resultCode, data);
}
}

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：

public Date date;

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

编辑：

对于你的后续问题：

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

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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