我正在修改访问预填充数据库的代码。我遇到了 nullPointerException 错误，我不知道发生了什么。我将发布我的代码，如果有人可以提供帮助，我将不胜感激。
活动：
public class Activity1c extends ListActivity {
IngredientHelper mDbHelper=null;
int char_property;
int char_name;
long a=1;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.act1c);
mDbHelper = new IngredientHelper(this);
Bundle extras = getIntent().getExtras();
char_name = extras.getInt("char_name");
char_property = extras.getInt("char_property");
char_name+=1;
char_property+=1;
Toast.makeText(Activity1c.this,
"The char_name you picked was " + char_name + " and the property was "+char_property,
Toast.LENGTH_LONG).show();
Cursor notesCursor = mDbHelper.fetchNote(a);
startManagingCursor(notesCursor);
// Create an array to specify the fields we want to display in the list (only TITLE)
String[] from = new String[]{IngredientHelper.COLUMN_TITLE,IngredientHelper.COLUMN_TITLE2};
// and an array of the fields we want to bind those fields to (in this case just text1)
int[] to = new int[]{R.id.craft_type_display,R.id.spec_type_display};
// Now create a simple cursor adapter and set it to display
SimpleCursorAdapter notes =
new SimpleCursorAdapter(this, R.layout.finalresult1, notesCursor, from, to);
setListAdapter(notes);
}///end main
}///end class
xml/act1c
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ListView android:id="@+id/android:list"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
<TextView android:id="@+id/android:empty"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>
xml/最终结果1
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical" >
<TextView
android:id="@+id/craft_type_display"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/spec_type_display"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
类/IngredientHelper
public class IngredientHelper extends SQLiteOpenHelper{
//we declare a bunch of useful constants
//the should be pretty obvious what they are!
private static final String DATABASE_PATH = "/data /data/com.android.Database_Practice_3_31_12/databases/";
private static final String DATABASE_NAME="infotest.sqlite";
private static final int SCHEMA_VERSION=1;
public static final String TABLE_NAME = "info";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_TITLE = "name";
public static final String COLUMN_TITLE2 = "phone";
public static final String COLUMN_TITLE3 = "fav_color";
public static final String COLUMN_TITLE4 = "home_city";
public SQLiteDatabase dbSqlite;
private final Context myContext;
public IngredientHelper(Context context) {
super(context, DATABASE_NAME, null, SCHEMA_VERSION);
this.myContext = context;
// check if exists and copy database from resource
//createDB();
}
@Override
public void onCreate(SQLiteDatabase db) {
// check if exists and copy database from resource
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public void createDatabase() {
createDB();
}
private void createDB() {
boolean dbExist = DBExists();
if (!dbExist) {
//By calling this method we create an empty database into the default system location
//We need this so we can overwrite that database with our database.
this.getReadableDatabase();
//now we copy the database we included!
copyDBFromResource();
}
}
private boolean DBExists() {
SQLiteDatabase db = null;
try {
String databasePath = DATABASE_PATH + DATABASE_NAME;
db = SQLiteDatabase.openDatabase(databasePath, null,
SQLiteDatabase.OPEN_READWRITE);
db.setLocale(Locale.getDefault());
db.setLockingEnabled(true);
db.setVersion(1);
} catch (SQLiteException e) {
Log.e("SqlHelper", "database not found");
}
if (db != null) {
db.close();
}
return db != null ? true : false;
}
private void copyDBFromResource() {
InputStream inputStream = null;
OutputStream outStream = null;
String dbFilePath = DATABASE_PATH + DATABASE_NAME;
try {
inputStream = myContext.getAssets().open(DATABASE_NAME);
outStream = new FileOutputStream(dbFilePath);
byte[] buffer = new byte[1024];
int length;
while ((length = inputStream.read(buffer)) > 0) {
outStream.write(buffer, 0, length);
}
outStream.flush();
outStream.close();
inputStream.close();
} catch (IOException e) {
throw new Error("Problem copying database from resource file.");
}
}
public void openDataBase() throws SQLException {
String myPath = DATABASE_PATH + DATABASE_NAME;
dbSqlite = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
@Override
public synchronized void close() {
if (dbSqlite != null)
{
dbSqlite.close();
}
super.close();
}
public Cursor getCursor() {
SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();
queryBuilder.setTables(TABLE_NAME);
String[] asColumnsToReturn = new String[] { COLUMN_ID,COLUMN_TITLE};
//make sure you get your search by string pass correctly!
Cursor mCursor = queryBuilder.query(dbSqlite, asColumnsToReturn, null,
null, null, null, null);
return mCursor;
}
public String getName(Cursor c) {
return(c.getString(1));
}
public Cursor fetchNote(long rowId) throws SQLException {
Cursor mCursor =
dbSqlite.query(true, TABLE_NAME, new String[] {
COLUMN_ID, COLUMN_TITLE,COLUMN_TITLE2,COLUMN_TITLE3,COLUMN_TITLE4}, COLUMN_ID + "=" + rowId, null,
null, null, null, null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
}
日志猫
04-04 19:54:50.764: E/AndroidRuntime(454): Uncaught handler: thread main exiting due to uncaught exception
04-04 19:54:50.774: E/AndroidRuntime(454): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.Database_Practice_3_31_12/com.android.Database_Practice_3_31_12.Activity1c}: java.lang.NullPointerException
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.ActivityThread.access$2200(ActivityThread.java:119)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.os.Handler.dispatchMessage(Handler.java:99)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.os.Looper.loop(Looper.java:123)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.ActivityThread.main(ActivityThread.java:4363)
04-04 19:54:50.774: E/AndroidRuntime(454): at java.lang.reflect.Method.invokeNative(Native Method)
04-04 19:54:50.774: E/AndroidRuntime(454): at java.lang.reflect.Method.invoke(Method.java:521)
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
04-04 19:54:50.774: E/AndroidRuntime(454): at dalvik.system.NativeStart.main(Native Method)
04-04 19:54:50.774: E/AndroidRuntime(454): Caused by: java.lang.NullPointerException
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.Database_Practice_3_31_12.IngredientHelper.fetchNote(IngredientHelper.java:173)
04-04 19:54:50.774: E/AndroidRuntime(454): at com.android.Database_Practice_3_31_12.Activity1c.onCreate(Activity1c.java:49)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-04 19:54:50.774: E/AndroidRuntime(454): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)