当我按下“显示”按钮（btnshow）时，它显示错误无法启动活动组件信息＆amp; Nullpointer异常。我怎么能解决这个问题.plz帮帮我......
Mainactivity.java
package com.mamun.sqltest;
import android.app.Activity;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity implements OnClickListener {
private Button add, delete, update, show, search;
private EditText etname, etaddress, etcell, etsearch;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
add = (Button) findViewById(R.id.btnadd);
delete = (Button) findViewById(R.id.btndelete);
update = (Button) findViewById(R.id.btnupdate);
show = (Button) findViewById(R.id.btnshow);
search = (Button) findViewById(R.id.btnsearch);
etname = (EditText) findViewById(R.id.etname);
etaddress = (EditText) findViewById(R.id.etaddress);
etcell = (EditText) findViewById(R.id.etcell);
etsearch = (EditText) findViewById(R.id.etsearch);
add.setOnClickListener(this);
delete.setOnClickListener(this);
update.setOnClickListener(this);
show.setOnClickListener(this);
search.setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btnadd:
boolean didItwork = true;
try {
String name = etname.getText().toString();
String address = etaddress.getText().toString();
String cell = etcell.getText().toString();
Dbtrial entry = new Dbtrial(MainActivity.this);
entry.open();
entry.createEntry(name, address, cell);
entry.close();
} catch (Exception e) {
didItwork = false;
String error = e.toString();
Dialog d = new Dialog(this);
d.setTitle("Error found");
TextView tv = new TextView(this);
tv.setText(error);
d.setContentView(tv);
d.show();
} finally {
if (didItwork) {
Dialog d = new Dialog(this);
d.setTitle("Saved");
TextView tv = new TextView(this);
tv.setText("Sucess");
d.setContentView(tv);
d.show();
}
}
break;
case R.id.btndelete:
try{String sRow1 = etsearch.getText().toString();
long lRow1 = Long.parseLong(sRow1);
Dbtrial ex1 = new Dbtrial(this);
ex1.open();
ex1.deleteEntry(lRow1);
ex1.close();
}catch (Exception e) {
String error = e.toString();
Dialog d = new Dialog(this);
d.setTitle("Error found");
TextView tv = new TextView(this);
tv.setText(error);
d.setContentView(tv);
d.show();
}
break;
case R.id.btnupdate:
try{
String sRow = etsearch.getText().toString();
long lRow= Long.parseLong(sRow);
String upname = etname.getText().toString();
String upaddress = etaddress.getText().toString();
String upcell = etcell.getText().toString();
Dbtrial ex = new Dbtrial(this);
ex.open();
ex.updateEntry(lRow,upname,upaddress,upcell);
ex.close();
}catch (Exception e) {
String error = e.toString();
Dialog d = new Dialog(this);
d.setTitle("Error found");
TextView tv = new TextView(this);
tv.setText(error);
d.setContentView(tv);
d.show();
}
break;
case R.id.btnshow:
Intent i = new Intent(this,Sqlview.class);
startActivity(i);
break;
case R.id.btnsearch:
try {
String s = etsearch.getText().toString();
long l= Long.parseLong(s);
Dbtrial hon = new Dbtrial(this);
hon.open();
String returnedNamed = hon.getName(l);
String returnedAddress = hon.getAddress(l);
String returnedCell = hon.getCell(l);
hon.close();
etname.setText(returnedNamed);
etaddress.setText(returnedAddress);
etcell.setText(returnedCell);
}catch (Exception e) {
String error = e.toString();
Dialog d = new Dialog(this);
d.setTitle("Error found");
TextView tv = new TextView(this);
tv.setText(error);
d.setContentView(tv);
d.show();
}
break;
default:
break;
}
}
}
的 Dbtrial.java 的
package com.mamun.sqltest;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class Dbtrial {
public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "name";
public static final String KEY_ADDRESS = "address";
public static final String KEY_CELL = "cell";
private static final String DATABASE_NAME = "Infodb";
private static final String DATABASE_TABLE = "Info";
private static final int DATABASE_VERSION = 3;
private DbHelper ourHelper;
private final Context ourContext;
private SQLiteDatabase ourDatabase;
private static class DbHelper extends SQLiteOpenHelper {
public DbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" + KEY_ROWID
+ " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_NAME
+ " TEXT NOT NULL , " + KEY_ADDRESS + " TEXT NOT NULL, "
+ KEY_CELL + " NUMBER NOT NULL );");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
}
public Dbtrial(Context c) {
ourContext = c;
}
public Dbtrial open() throws SQLException {
ourHelper = new DbHelper(ourContext);
ourDatabase = ourHelper.getWritableDatabase();
return this;
}
public void close() {
ourHelper.close();
}
public long createEntry(String name, String address, String cell) {
// TODO Auto-generated method stub
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, name);
cv.put(KEY_ADDRESS, address);
cv.put(KEY_CELL, cell);
return ourDatabase.insert(DATABASE_TABLE, null, cv);
}
public String getData() {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null,
null, null);
String result = "";
int iId = c.getColumnIndex(KEY_NAME);
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
result = result + c.getString(iId) + "\n";//
}
return result;
}
public String getName(long l) throws SQLException {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "="
+ l, null, null, null, null);
if (c != null) {
c.moveToFirst();
String name = c.getString(1);
return name;
}
return null;
}
public String getAddress(long l) throws SQLException {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "="
+ l, null, null, null, null);
if (c != null) {
c.moveToFirst();
String address = c.getString(2);
return address;
}
return null;
}
public String getCell(long l) throws SQLException {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, KEY_ROWID + "="
+ l, null, null, null, null);
if (c != null) {
c.moveToFirst();
String cell = c.getString(3);
return cell;
}
return null;
}
public void updateEntry(long lRow, String upname, String upaddress,
String upcell) throws SQLException {
ContentValues cvUpdate = new ContentValues();
cvUpdate.put(KEY_NAME, upname);
cvUpdate.put(KEY_ADDRESS, upaddress);
cvUpdate.put(KEY_CELL, upcell);
ourDatabase.update(DATABASE_TABLE, cvUpdate, KEY_ROWID + "=" + lRow,
null);
}
public void deleteEntry(long lRow1) throws SQLException {
ourDatabase.delete(DATABASE_TABLE, KEY_ROWID + "=" + lRow1, null);
}
public String getData2() {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null,
null, null);
String result = "";
int iName = c.getColumnIndex(KEY_NAME);
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
result = result + c.getString(iName) + "\n";//
}
return result;
}
public String getData3() {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null,
null, null);
String result = "";
int iAddress = c.getColumnIndex(KEY_ADDRESS);
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
result = result + c.getString(iAddress) + "\n";
}
return result;
}
public String getData4() {
String[] columns = new String[] { KEY_ROWID, KEY_NAME, KEY_ADDRESS,
KEY_CELL };//
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null,
null, null);
String result = "";
int iCell = c.getColumnIndex(KEY_CELL);
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
result = result + c.getString(iCell) + "\n";
}
return result;
}
}
的 Sqlview.java 的
package com.mamun.sqltest;
import java.util.ArrayList;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
public class Sqlview extends Activity {
// data source
private String alldata;
private Dbtrial dbAdapter;
// adapter
private DataAdapter adapter;
// view
private ListView lvinfo;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sqlview);
// //
dbAdapter = new Dbtrial(this);
dbAdapter.open();
alldata = dbAdapter.getData();
dbAdapter.close();
lvinfo = (ListView) findViewById(R.id.lvinfo);
adapter = new DataAdapter(this, alldata);
lvinfo.setAdapter(adapter);
lvinfo.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> listview, View v, int position,
long id) {
Toast.makeText(getApplicationContext(), "Selected Book: "+position, Toast.LENGTH_LONG).show();
}
});
}
}
*的 DataAdapter的 *
package com.mamun.sqltest;
import java.util.ArrayList;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.Toast;
public class DataAdapter extends ArrayAdapter<Dbtrial>{
private Activity context;
private static ArrayList<Dbtrial> items;
private LayoutInflater inflater;
public DataAdapter(Context context, String alldata) {
super(context, R.layout.info_item, items);
this.context=(Activity)context;
this.items=items;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View v=convertView;
if(v==null)
{
// create new view
inflater=context.getLayoutInflater();
v=inflater.inflate(R.layout.info_item, null);
TextView tvid=(TextView)v.findViewById(R.id.tvid);
TextView tvname=(TextView)v.findViewById(R.id.tvname);
TextView tvaddress=(TextView)v.findViewById(R.id.tvaddress);
TextView tvcell=(TextView)v.findViewById(R.id.tvcell);
Dbtrial b=items.get(position);
tvid.setText(b.getData());
tvname.setText(b.getData2());
tvaddress.setText(b.getData3());
tvcell.setText(b.getData4());
tvname.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Toast.makeText(context, "I am a title", Toast.LENGTH_LONG).show();
}
});
}
else
{
}
return v;
}
}
xml文件是：
* activity_main.xml中*`
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Name"
android:textAppearance="?android:attr/textAppearanceLarge" />
<EditText
android:id="@+id/etname"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10" >
<requestFocus />
</EditText>
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Address"
android:textAppearance="?android:attr/textAppearanceLarge" />
<EditText
android:id="@+id/etaddress"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10" />
<TextView
android:id="@+id/textView3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Cell"
android:textAppearance="?android:attr/textAppearanceLarge" />
<EditText
android:id="@+id/etcell"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:inputType="phone" />
<TableRow
android:id="@+id/tableRow1"
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<Button
android:id="@+id/btnadd"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="@string/btn_add" />
<Button
android:id="@+id/btndelete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Delete" />
<Button
android:id="@+id/btnupdate"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Update" />
<Button
android:id="@+id/btnshow"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Show" />
</TableRow>
<TextView
android:id="@+id/textView4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Search here"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="@+id/etsearch"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10"
android:hint="search by id"
android:inputType="number" />
<Button
android:id="@+id/btnsearch"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Search" />
</LinearLayout>
的 sqlview.xml 的
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<ListView
android:id="@+id/lvinfo"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" >
</ListView>
</LinearLayout>
*的 * info_item.xml *
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TableLayout
android:layout_width="match_parent"
android:layout_height="wrap_content" >
<TableRow
android:id="@+id/tableRow1"
android:layout_width="wrap_content"
android:layout_height="wrap_content" >
<TextView
android:id="@+id/tvid"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Id"
android:layout_weight="2"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="@+id/tvaddress"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="address"
android:layout_weight="1"
android:layout_gravity="right"
/>
</TableRow>
<TableRow
android:id="@+id/tableRow2"
android:layout_width="wrap_content"
android:layout_height="wrap_content" >
<TextView
android:id="@+id/tvname"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="name"
android:layout_weight="2"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="@+id/tvcell"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:text="cell"
android:layout_weight="1"
android:layout_gravity="right"/>
</TableRow>
</TableLayout>
</LinearLayout>
的 logcat的 的
12-07 07:42:46.945: E/AndroidRuntime(1259): FATAL EXCEPTION: main
12-07 07:42:46.945: E/AndroidRuntime(1259): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mamun.sqltest/com.mamun.sqltest.Sqlview}: java.lang.NullPointerException
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.ActivityThread.access$600(ActivityThread.java:141)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.os.Handler.dispatchMessage(Handler.java:99)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.os.Looper.loop(Looper.java:137)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.ActivityThread.main(ActivityThread.java:5039)
12-07 07:42:46.945: E/AndroidRuntime(1259): at java.lang.reflect.Method.invokeNative(Native Method)
12-07 07:42:46.945: E/AndroidRuntime(1259): at java.lang.reflect.Method.invoke(Method.java:511)
12-07 07:42:46.945: E/AndroidRuntime(1259): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-07 07:42:46.945: E/AndroidRuntime(1259): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-07 07:42:46.945: E/AndroidRuntime(1259): at dalvik.system.NativeStart.main(Native Method)
12-07 07:42:46.945: E/AndroidRuntime(1259): Caused by: java.lang.NullPointerException
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.widget.ListView.setAdapter(ListView.java:462)
12-07 07:42:46.945: E/AndroidRuntime(1259): at com.mamun.sqltest.Sqlview.onCreate(Sqlview.java:38)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.Activity.performCreate(Activity.java:5104)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
12-07 07:42:46.945: E/AndroidRuntime(1259): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
12-07 07:42:46.945: E/AndroidRuntime(1259): ... 11 more
答案 0 :(得分：1)
传递给items超级构造函数的ArrayAdapter为null。
答案 1 :(得分：0)
我觉得问题在于Dbtrial构造函数。您正在使用ourDatabase = ourHelper.getWritableDatabase();以写入模式getData()和querymethod打开数据库。要从数据库读取数据，它应以可读模式打开。这是因为它将空数据返回到alldata = dbAdapter.getData();并且不会初始化适配器并且会抛出错误。
答案 2 :(得分：0)
尝试删除NUMBER NOT NULL后的空格