使用数据库时遇到问题。当我运行我的SQLView.java时，我得到一个致命的异常。我将发布所有与数据库相关的代码。
在数据库类（第71行）和SQLView类（第14行）上查看我的注释行。也许有什么不对劲？我尝试了很多东西，比如说，这是null。
此外，我已阅读本网站上所有相关的nullpointerexception-问题。
开始：我的数据库类：
package com.jacob.eindproject;
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;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import java.sql.*;
public class Database {
public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "persons_name";
public static final String KEY_HOTNESS = "persons_hotness";
private static final String DATABASE_NAME = "Databasedb";
private static final String DATABASE_TABLE = "peopleTable";
private static final int DATABASE_VERSION = 1;
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_HOTNESS + " TEXT NOT NULL);"
);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);
onCreate(db);
}
public void close(Database database) {
// TODO Auto-generated method stub
}
}
public Database(Context c){
ourContext = c;
}
public Database open() throws SQLException{
ourHelper = new DbHelper(ourContext);
ourDatabase = ourHelper.getWritableDatabase();
return this;
}
public void close() {
ourHelper.close(); //This is line 71, where also an error is given, maybe there should me text between the brackets ()?
}
public long createEntry(String name, String hotness) {
ContentValues cv = new ContentValues();
cv.put(KEY_NAME, name);
cv.put(KEY_HOTNESS, hotness);
return ourDatabase.insert(DATABASE_TABLE, null, cv);
}
public String getData() {
// TODO Auto-generated method stub
String[] columns = new String[]{ KEY_ROWID, KEY_NAME, KEY_HOTNESS};
Cursor c = ourDatabase.query(DATABASE_TABLE, columns, null, null, null, null, null);
String result = "";
int iRow = c.getColumnIndex(KEY_ROWID);
int iName = c.getColumnIndex(DATABASE_NAME);
int iHotness = c.getColumnIndex(KEY_HOTNESS);
for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()){
result = result + c.getString(iRow) + " " + c.getString(iName) + " " + c.getString(iHotness) + "\n";
}
return result;
}
}
SQLite类，用于修复输入：
package com.jacob.eindproject;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.app.Activity;
import android.app.Dialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.view.View.OnClickListener;
public class SQLite extends Activity implements View.OnClickListener {
Button sqlUpdate, sqlView;
EditText sqlName, sqlHotness;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sqllite);
sqlUpdate = (Button) findViewById(R.id.bSQLUpdate);
sqlName = (EditText) findViewById(R.id.etSQLName);
sqlHotness = (EditText) findViewById(R.id.etSQLHotness);
sqlView = (Button) findViewById(R.id.bSQLopenView);
sqlView.setOnClickListener((android.view.View.OnClickListener) this);
sqlUpdate.setOnClickListener((android.view.View.OnClickListener) this);
}
public void onClick(View arg0) {
switch (arg0.getId()) {
case R.id.bSQLUpdate:
boolean didItWork = true;
try{
String name = sqlName.getText().toString();
String hotness = sqlHotness.getText().toString();
Database entry = new Database(SQLite.this);
entry.open();
entry.createEntry(name, hotness);
entry.close();
}catch (Exception e ){
didItWork = false;
}finally{
if (didItWork){
Dialog d = new Dialog(this);
d.setTitle("Heak Yeay");
TextView tv = new TextView(this);
tv.setText("Succes");
d.setContentView(tv);
d.show();
}
}
break;
case R.id.bSQLopenView:
Intent i = new Intent("com.jacob.eindproject.SQLVIEW");
startActivity(i);
}
}
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
}
}
之后，我的SQLView类，来查看SQLite类的输入：
package com.jacob.eindproject;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class SQLView extends Activity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sqlview);
TextView tv = (TextView) findViewById(R.id.tvSQLinfo);
Database info = new Database(this); //as you can see in the logcat, this is line 14, where the error is. Maybe the "this" isn't right?
info.open();
String data = info.getData();
info.close();
tv.setText(data);
}
}
现在，我的xml文件，也许我还没有配置好按钮，或者什么？
SQLView.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TableLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/tableLayout1">
<TableRow>
<TextView android:text="@string/Names" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1"/>
<TextView android:text="@string/Hotness" android:layout_width="fill_parent" android:layout_height="fill_parent" android:layout_weight="1" />
</TableRow>
</TableLayout>
<TextView android:id="@+id/tvSQLinfo" android:layout_width="fill_parent" android:layout_height="fill_parent" android:text="@string/info"/>
</LinearLayout>
sqllite.xml：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/Naam"
android:text="@string/Naam"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceSmall" />
<EditText
android:id="@+id/etSQLName"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</EditText>
<TextView
android:id="@+id/hotness"
android:text="@string/hotnessscale"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
<EditText
android:id="@+id/etSQLHotness"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</EditText>
<Button
android:id="@+id/bSQLUpdate"
android:text="@string/Update"
android:layout_width="wrap_content"
android:layout_height="wrap_content" ></Button>
<Button
android:id="@+id/bSQLopenView"
android:text="@string/View"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
></Button>
</LinearLayout>
菜单类，用于修复菜单，使用OnListItemClick（其中还有一些其他活动，例如Overgewicht。不要介意这些，我猜......？）：
package com.jacob.eindproject;
import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class Menu extends ListActivity implements OnItemClickListener {
String classes[] = { "BMI- Calculator", "Ondergewicht", "Gezond Gewicht", "Overgewicht", "Database", "Bekijk Database"};
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setListAdapter(new ArrayAdapter<String>(Menu.this, android.R.layout.simple_list_item_1, classes));
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
//Positie 0 is het eerste item (dus de BMI-Calculator.)
super.onListItemClick(l, v, position, id);
switch(position)
{
case 0:
Intent openStartingPoint = new Intent(getApplicationContext(),MainActivity.class);
startActivity(openStartingPoint);
break;
case 1:
Intent openOndergewicht = new Intent(getApplicationContext(),Ondergewicht.class);
startActivity(openOndergewicht);
break;
case 2:
Intent openGezondgewicht = new Intent(getApplicationContext(),Gezond_gewicht.class);
startActivity(openGezondgewicht);
break;
case 3:
Intent openOvergewicht = new Intent(getApplicationContext(),Overgewicht.class);
startActivity(openOvergewicht);
break;
case 4:
Intent openDatabase = new Intent(getApplicationContext(),SQLite.class);
startActivity(openDatabase);
break;
case 5:
Intent openViewdatabase = new Intent(getApplicationContext(),SQLView.class);
startActivity(openViewdatabase);
break;
}
}
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
// TODO Auto-generated method stub
}
}
我的Android清单文件:(再次，我已经宣布了其他一些事情，不介意这些！）
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.jacob.eindproject"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.jacob.eindproject.Menu"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.jacob.eindproject.Inleiding"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.jacob.eindproject.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.jacob.eindproject.Ondergewicht"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.jacob.eindproject.Gezond_gewicht"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.jacob.eindproject.Overgewicht"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.jacob.eindproject.Database"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.jacob.eindproject.DATABASE" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name=".SQLView"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.jacob.eindproject.SQLVIEW" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="com.jacob.eindproject.SQLite"
android:label="@string/app_name" >
<intent-filter>
<action android:name="com.jacob.eindproject.SQLITE" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
</manifest>
最后，我的LogCat，向您显示错误：
12-14 11:04:18.227: E/AndroidRuntime(1577): FATAL EXCEPTION: main
12-14 11:04:18.227: E/AndroidRuntime(1577): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jacob.eindproject/com.jacob.eindproject.SQLView}: java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it.
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.ActivityThread.access$600(ActivityThread.java:141)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.os.Handler.dispatchMessage(Handler.java:99)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.os.Looper.loop(Looper.java:137)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.ActivityThread.main(ActivityThread.java:5103)
12-14 11:04:18.227: E/AndroidRuntime(1577): at java.lang.reflect.Method.invokeNative(Native Method)
12-14 11:04:18.227: E/AndroidRuntime(1577): at java.lang.reflect.Method.invoke(Method.java:525)
12-14 11:04:18.227: E/AndroidRuntime(1577): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
12-14 11:04:18.227: E/AndroidRuntime(1577): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-14 11:04:18.227: E/AndroidRuntime(1577): at dalvik.system.NativeStart.main(Native Method)
12-14 11:04:18.227: E/AndroidRuntime(1577): Caused by: java.lang.IllegalStateException: Couldn't read row 0, col -1 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it.
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.database.CursorWindow.nativeGetString(Native Method)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.database.CursorWindow.getString(CursorWindow.java:434)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:51)
12-14 11:04:18.227: E/AndroidRuntime(1577): at com.jacob.eindproject.Database.getData(Database.java:95)
12-14 11:04:18.227: E/AndroidRuntime(1577): at com.jacob.eindproject.SQLView.onCreate(SQLView.java:16)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.Activity.performCreate(Activity.java:5133)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-14 11:04:18.227: E/AndroidRuntime(1577): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
12-14 11:04:18.227: E/AndroidRuntime(1577): ... 11 more
编辑：
我现在有一个新错误，请看看我的LogCat。我想是因为我的列集错了？提前谢谢。
答案 0 :(得分：1)
NPE发生在Database类的第71行，构造函数中的某个位置或初始化变量时（这是堆栈跟踪中的<init>代表的）。
我刚刚读到你自己想出来了。所以这里唯一可以为null的是ourHelper。
这真的是你的代码吗？
public void close() {
} {
ourHelper.close(); //This is line 71, where also an error is given, maybe there should me text between the brackets ()?
}
这里的括号有问题。我不确定为什么这会编译，但我猜它确实如此，并且编译器执行
{
ourHelper.close();
}
在实例化类时立即。
将此更改为
public void close() {
ourHelper.close();
}
你应该没事。