Android 自定义SimpleCursorAdapter、数据库查询和NullPointerException
我试图从数据库中填充ListView,并使用奇特的删除按钮为每一行添加香料。所以我制作了列表活动和自定义SimpleCorsorAdapter 这是主要的ListView活动:Android 自定义SimpleCursorAdapter、数据库查询和NullPointerException,android,database,sqlite,adapter,android-listview,Android,Database,Sqlite,Adapter,Android Listview,我试图从数据库中填充ListView,并使用奇特的删除按钮为每一行添加香料。所以我制作了列表活动和自定义SimpleCorsorAdapter 这是主要的ListView活动: public class EditEntries extends ListActivity { Cursor cursor; DBAdapter db = new DBAdapter(this); private static String[] FROM = { _ID, SCORE_CO
public class EditEntries extends ListActivity {
Cursor cursor;
DBAdapter db = new DBAdapter(this);
private static String[] FROM = { _ID, SCORE_COLUMN,
"date(time, 'localtime')", };
private static int[] TO = { R.id.rowid, R.id.title, R.id.time, };
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.entries_list);
try {
cursor = getEvents();
showEvents(cursor);
} finally {
db.close();
}
}
private void showEvents(Cursor cursor) {
// Set up data binding
SMSimpleCursorAdapter adapter = new SMSimpleCursorAdapter(this,
R.layout.entries_list_item, cursor, FROM, TO);
setListAdapter(adapter);
}
private Cursor getEvents() {
db.open();
cursor = db.getAllScores();
startManagingCursor(cursor);
return cursor;
}
void delRow() { // this is method for deleting row by _id
db.open();
db.deleteScore(3); // here will be TAG with _id from adapter,
db.close(); // for now I just use hardcoded _id
}
}
这是定制的SimpleCrsorAdapter:
public class SMSimpleCursorAdapter extends SimpleCursorAdapter{
Cursor c;
Context context;
Activity activity;
public SMSimpleCursorAdapter(Context context, int layout, Cursor c,
String[] from, int[] to) {
super(context, layout, c, from, to);
this.c = c;
this.context=context;
this.activity=(Activity) context;
}
EditEntries dbDel = new EditEntries(); //from previous code sample
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null)
convertView = View.inflate(context, R.layout.entries_list_item, null);
View row = convertView;
c.moveToPosition(position);
TextView score = (TextView) convertView.findViewById(R.id.title);
TextView time = (TextView) convertView.findViewById(R.id.time);
TextView id = (TextView) convertView.findViewById(R.id.rowid);
id.setText(c.getString(0));
time.setText(c.getString(2));
score.setText(c.getString(1));
String daTag = c.getString(1);
ImageButton delButton = (ImageButton) convertView.findViewById(R.id.delButton);
delButton.setFocusable(true);
delButton.setClickable(true);
//delButton.setTag(daTag);
delButton.setOnClickListener(new OnClickListener() { //Click listener fro delete button
@Override
public void onClick(View view) {
dbDel.delRow(); //this is "delete row" method from previos code sample
}
});
return(row);
}
}
当我点击删除按钮时,所有这些东西都会让我产生NullPointerException。
我是android新手,假设我错过了一些显而易见的东西
日志:
错误/AndroidRuntime(14027):致命异常:主
错误/AndroidRuntime(14027):java.lang.NullPointerException
错误/AndroidRuntime(14027):位于android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
错误/AndroidRuntime(14027):位于android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
ERROR/AndroidRuntime(14027):位于namespace.DBAdapter.open(DBAdapter.java:66)
错误/AndroidRuntime(14027):位于namespace.EditEntries.delRow(EditEntries.java:50)
ERROR/AndroidRuntime(14027):位于namespace.SMSimpleCursorAdapter$1.onClick(SMSimpleCursorAdapter.java:64)
错误/AndroidRuntime(14027):在android.view.view.performClick(view.java:2414)处
错误/AndroidRuntime(14027):在android.view.view$PerformClick.run(view.java:8838)
ERROR/AndroidRuntime(14027):位于android.os.Handler.handleCallback(Handler.java:587)
错误/AndroidRuntime(14027):在android.os.Handler.dispatchMessage(Handler.java:92)处
ERROR/AndroidRuntime(14027):位于android.os.Looper.loop(Looper.java:123)
错误/AndroidRuntime(14027):位于android.app.ActivityThread.main(ActivityThread.java:4680)
错误/AndroidRuntime(14027):位于java.lang.reflect.Method.Invokenactive(本机方法)
ERROR/AndroidRuntime(14027):位于java.lang.reflect.Method.invoke(Method.java:521)
ERROR/AndroidRuntime(14027):位于com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
ERROR/AndroidRuntime(14027):位于com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
错误/AndroidRuntime(14027):位于dalvik.system.NativeStart.main(本机方法)
问题出在SMSimpleCursorAdapter代码中:
EditEntries dbDel = new EditEntries(); //from previous code sample
您创建了一个新对象,但它不是托管活动(例如,不会调用onCreate方法)。当您尝试第二次(从适配器)创建NPE时,NPE可能来自您的DBAdapter
快速修复:
EditEntries dbDel; //from previous code sample
public SMSimpleCursorAdapter(Context context, int layout, Cursor c,
String[] from, int[] to) {
super(context, layout, c, from, to);
this.c = c;
this.context = context;
this.activity = (Activity) context;
this.dbDel = (EditEntries) context;
}
如果您不想只是快速修复,那么以下是一个更好的解决方案:
你能发布
logcat
输出吗?是的,正如我所怀疑的,日志支持了我的理论。希望我的回答有帮助。