我正在编写 big nerd ranch 指南的 Android 编程的第二部分。出于某种原因,当我尝试运行该应用程序时,它在启动时崩溃,日志 cat 显示在线抛出了一个空指针异常:
UUID crimeID = (UUID)getArguments().getSerializable(EXTRA_CRIME_ID);
为什么 EXTRA_CRIME_ID 返回空值?
这是抛出异常的我的犯罪列表 fragment :
package com.bignerdranch.android.criminalintent;
import java.util.UUID;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.text.Editable;
import android.text.TextWatcher;
import android.text.format.DateFormat;
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.CompoundButton.OnCheckedChangeListener;
import android.widget.EditText;
public class CrimeFragment extends Fragment {
public static final String EXTRA_CRIME_ID =
"com.bignerdranch.android.criminalintent.crime_id";
private Crime mCrime;
private EditText mTitleField;
private Button mDateButton;
private CheckBox mSolvedCheckBox;
@Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
**UUID crimeID = (UUID)getArguments().getSerializable(EXTRA_CRIME_ID);**
mCrime = CrimeLab.get(getActivity()).getCrime(crimeID);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState){
View v =inflater.inflate(R.layout.fragment_crime, parent, false);
mTitleField = (EditText)v.findViewById(R.id.crime_title);
mTitleField.setText(mCrime.getTitle());
mTitleField.addTextChangedListener(new TextWatcher() {
public void onTextChanged(CharSequence c, int start, int before, int count){
mCrime.setTitle(c.toString());
}
public void beforeTextChanged(CharSequence c, int start, int count, int after){
//left blank
}
public void afterTextChanged(Editable c){
//this one to
}
});
mDateButton = (Button)v.findViewById(R.id.crime_date);
mDateButton.setText(DateFormat.format("hh:mm:ss", mCrime.getDate()));
mDateButton.setEnabled(false);
mSolvedCheckBox = (CheckBox)v.findViewById(R.id.crime_solved);
mSolvedCheckBox.setChecked(mCrime.isSolved());
mSolvedCheckBox.setOnCheckedChangeListener(new OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
//set the crimes solved property
mCrime.setSolved(isChecked);
}
});
return v;
}
}
最佳答案
我还没有定义任何参数,所以我的 getArguments() 返回 null。我应该用
UUID crimeId = (UUID)getActivity().getIntent().getSerializableExtra(EXTRA_CRIME_ID);
相反。
----2014 年 12 月 16 日更新----
正如 njzk2 所指出的,我将 fragment 链接到 Activity ,以防止它被用于另一个 Activity 。 BigNerdRanch 书中出于简单原因将其链接到前面章节中的 Activity ,然后让读者在后面更改它并添加方法:
public static CrimeFragment newInstance(UUID crimeId){
Bundle args = new Bundle();
args.putSerializable(EXTRA_CRIME_ID, crimeId);
CrimeFragment fragment = new CrimeFragment();
fragment.setArguments(args);
//pass UUID from extra
return fragment;
}
并更改 UUID crimeId = (UUID)getActivity().getIntent().getSerializableExtra(EXTRA_CRIME_ID);到
UUID crimeId = (UUID)getArguments().getSerializable(EXTRA_CRIME_ID);
关于java - UUID 返回空指针异常,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/27319366/