java – 由于NullPointerException导致应用程序崩溃
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我正在使用listview,在单击时打开一个包含edittext和按钮的对话框.单击按钮时,editText中输入的值将保存在listView项目的textView中,该项目之前已按过该项目.问题是如果我重新打开应用程序,则不再保存该值.我尝试使用sharedPrefences进行保存但它崩溃并显示3 nullpointerexception并且无法处理它们.
这是我的：
Carnet.java
package com.cngcnasaud.orar;
import android.app.TabActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TabHost;
import android.widget.TabHost.TabSpec;
@SuppressWarnings("deprecation")
public class Carnet extends TabActivity {
// TabSpec Names
private static final String NOTA_SPEC = "Note";
private static final String ABSENTE_SPEC = "Absente";
private static final String MEDII_SPEC = "Medii";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.carnet);
TabHost tabHost = getTabHost();
TabSpec NotaSpec = tabHost.newTabSpec(NOTA_SPEC);
// Tab Icon
NotaSpec.setIndicator(NOTA_SPEC, getResources().getDrawable(R.drawable.nota_open));
Intent notaIntent = new Intent(this, Note.class);
// Tab Content
NotaSpec.setContent(notaIntent);
TabSpec AbsenteSpec = tabHost.newTabSpec(ABSENTE_SPEC);
AbsenteSpec.setIndicator(ABSENTE_SPEC, getResources().getDrawable(R.drawable.nota_open));
Intent absenteIntent = new Intent(this, Absente.class);
AbsenteSpec.setContent(absenteIntent);
TabSpec MediiSpec = tabHost.newTabSpec(MEDII_SPEC);
AbsenteSpec.setIndicator(MEDII_SPEC, getResources().getDrawable(R.drawable.nota_open));
Intent mediiIntent = new Intent(this, MediiL.class);
AbsenteSpec.setContent(mediiIntent);
// Adding all TabSpec to TabHost
tabHost.addTab(NotaSpec);
tabHost.addTab(AbsenteSpec);
tabHost.addTab(MediiSpec);
}
}
Note.java
package com.cngcnasaud.orar;
import java.util.ArrayList;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.view.Menu;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
public class Note extends Activity {
private static final ListAdapter NoteAdapter = null;
ListView lv;
Context context;
ArrayList<?> prgmName;
TextView text;
public static String[] prgmNameList = { "Romana - ", "Matematica - ",
"Lb. Engleza - ", "Lb. Germana/Franceza - ", "Istorie - ",
"Geografie - ", "Biologie - ", "Fizica - ", "Ed. Fizica - " };
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.note_listview);
text = (TextView) findViewById(R.id.textView2);
context = this;
lv = (ListView) findViewById(R.id.listView);
lv.setAdapter(new NoteAdapter(this, prgmNameList, null));
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
protected void onStop() {
// TODO Auto-generated method stub
NoteAdapter adapter = (NoteAdapter) lv.getAdapter();
// Variable is public for clarity.
String toSave = EncodeDecode.encode(adapter.savedEntries);
SharedPreferences.Editor editor = getSharedPreferences("LV Data",
MODE_PRIVATE).edit();
editor.putString("TVEntries", toSave);
editor.commit();
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
SharedPreferences prefs = getSharedPreferences("LV Data", MODE_PRIVATE);
String encoded = prefs.getString("TVEntries", "");
String[] entries;
if (encoded.equals(""))
entries = null;
else
entries = EncodeDecode.decode(encoded);
NoteAdapter adapter = (NoteAdapter) lv.getAdapter();
adapter.savedEntries = entries;
lv.setAdapter(adapter);
super.onResume();
}
}
和NoteAdapter.java：
package com.cngcnasaud.orar;
import java.util.Arrays;
import android.app.Dialog;
import android.content.Context;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;
public class NoteAdapter extends BaseAdapter {
String[] result;
Context context;
int[] imageId;
private static LayoutInflater inflater = null;
private Dialog dialog;
String[] savedEntries;
String[] saved = null;
public NoteAdapter(Note note, String[] saved, String[] prgmNameList) {
// TODO Auto-generated constructor stub
result = prgmNameList;
context = note;
inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (saved == null) {
savedEntries = new String[result.length];
Arrays.fill(savedEntries, "");
} else
savedEntries = saved;
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return result.length;
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return savedEntries[position];
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
public class Holder {
TextView tv;
ImageView img;
public TextView text;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
final Holder holder = new Holder();
View rowView;
rowView = inflater.inflate(R.layout.note_items, null);
holder.tv = (TextView) rowView.findViewById(R.id.textView1);
holder.text = (TextView) rowView.findViewById(R.id.textView2);
holder.text.setText(savedEntries[position]);
holder.img = (ImageView) rowView.findViewById(R.id.imageView1);
rowView.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
dialog = new Dialog(context);
dialog.setContentView(R.layout.dialog);
dialog.setTitle("Materie:" + result[position]);
final EditText txtMode = (EditText) dialog
.findViewById(R.id.dialog);
Button btnSave = (Button) dialog.findViewById(R.id.bsave);
btnSave.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
String data = txtMode.getText().toString();
holder.text.setText(data);
savedEntries[position] = data;
dialog.dismiss();
Log.d("data", data);
}
});
dialog.show();
}
});
return rowView;
}
}
logcat的：
04-18 19:27:28.558: E/AndroidRuntime(1419): FATAL EXCEPTION: main
04-18 19:27:28.558: E/AndroidRuntime(1419): Process: com.cngcnasaud.orar, PID: 1419
04-18 19:27:28.558: E/AndroidRuntime(1419): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cngcnasaud.orar/com.cngcnasaud.orar.Carnet}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cngcnasaud.orar/com.cngcnasaud.orar.Note}: java.lang.NullPointerException
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.os.Handler.dispatchMessage(Handler.java:102)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.os.Looper.loop(Looper.java:136)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.main(ActivityThread.java:5017)
04-18 19:27:28.558: E/AndroidRuntime(1419): at java.lang.reflect.Method.invokeNative(Native Method)
04-18 19:27:28.558: E/AndroidRuntime(1419): at java.lang.reflect.Method.invoke(Method.java:515)
04-18 19:27:28.558: E/AndroidRuntime(1419): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-18 19:27:28.558: E/AndroidRuntime(1419): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-18 19:27:28.558: E/AndroidRuntime(1419): at dalvik.system.NativeStart.main(Native Method)
04-18 19:27:28.558: E/AndroidRuntime(1419): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cngcnasaud.orar/com.cngcnasaud.orar.Note}: java.lang.NullPointerException
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2035)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:749)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.widget.TabHost.setCurrentTab(TabHost.java:413)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.widget.TabHost.addTab(TabHost.java:240)
04-18 19:27:28.558: E/AndroidRuntime(1419): at com.cngcnasaud.orar.Carnet.onCreate(Carnet.java:45)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.Activity.performCreate(Activity.java:5231)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-18 19:27:28.558: E/AndroidRuntime(1419): ... 11 more
04-18 19:27:28.558: E/AndroidRuntime(1419): Caused by: java.lang.NullPointerException
04-18 19:27:28.558: E/AndroidRuntime(1419): at com.cngcnasaud.orar.NoteAdapter.getCount(NoteAdapter.java:46)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.widget.ListView.setAdapter(ListView.java:480)
04-18 19:27:28.558: E/AndroidRuntime(1419): at com.cngcnasaud.orar.Note.onCreate(Note.java:34)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.Activity.performCreate(Activity.java:5231)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-18 19:27:28.558: E/AndroidRuntime(1419): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-18 19:27:28.558: E/AndroidRuntime(1419): ... 21 more
Carnet.java第45行：
tabHost.addTab(NotaSpec);
NoteAdapter.java第46行：
return result.length;
Note.java第34行：
lv.setAdapter(new NoteAdapter(this, prgmNameList, null));
解决方法:
这里的String数组为null：
NoteAdapter.java第46行：
return result.length;
因为是一个类字段,您可以从参数中填充构造函数：
public NoteAdapter(Note note, String[] saved, String[] prgmNameList) {
// TODO Auto-generated constructor stub
result = prgmNameList;
你在这里传递为null(作为第二个参数传递,它应该是第三个)：
Note.java第34行：
lv.setAdapter(new NoteAdapter(this, prgmNameList, null));
传递它作为参数是没有意义的,因为它是一个公共常量(public static final).
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