自定义SimpleCursorAdapter,数据库查询和NullPointerException异常 [英] Custom SimpleCursorAdapter, database query and NullPointerException
问题描述
我试图使ListView的填充从数据库,和香料的每一行与花哨的删除按钮。所以我做了名单的活动和定制SimpleCursorAdapter。
这是主要的ListView活动:
公共类EditEntries扩展ListActivity {
光标光标;
DBAdapter DB =新DBAdapter(本);
私有静态的String [] FROM = {_ID,SCORE_COLUMN,
日期(时间,'本地时间'),};
私有静态诠释[] TO = {R.id.rowid,R.id.title,R.id.time,};
公共无效的onCreate(包savedInstanceState){
super.onCreate(savedInstanceState);
的setContentView(R.layout.entries_list);
尝试 {
光标= getEvents();
showEvents(光标);
} 最后 {
db.close();
}
}
私人无效showEvents(光标指针){
//设置数据绑定
SMSimpleCursorAdapter适配器=新SMSimpleCursorAdapter(这一点,
R.layout.entries_list_item,光标,发件人,收件人);
setListAdapter(适配器);
}
私人光标getEvents(){
db.open();
光标= db.getAllScores();
startManagingCursor(光标);
返回游标;
}
无效delRow(){//这是一种通过_id删除行
db.open();
db.deleteScore(3); //这里将TAG与_id的适配器,
db.close(); //现在我只是用硬codeD _id
}
}
这是自SimpleCursorAdapter:
公共类SMSimpleCursorAdapter扩展SimpleCursorAdapter {
光标C;
上下文语境;
活动活性;
公共SMSimpleCursorAdapter(上下文的背景下,INT布局,光标C,
的String []从,INT []键){
超(背景下,布局,C,从,到);
this.c = C;
this.context =背景;
this.activity =(活动)范围内;
}
EditEntries dbDel =新EditEntries(); //从previous code样品
@覆盖
公共查看getView(INT位置,查看convertView,ViewGroup中父){
如果(convertView == NULL)
convertView = View.inflate(背景下,R.layout.entries_list_item,NULL);
查看排= convertView;
c.moveToPosition(位置);
TextView的得分=(TextView中)convertView.findViewById(R.id.title);
TextView的时间=(TextView中)convertView.findViewById(R.id.time);
TextView的ID =(TextView中)convertView.findViewById(R.id.rowid);
id.setText(c.getString(0));
time.setText(c.getString(2));
score.setText(c.getString(1));
串daTag = c.getString(1);
的ImageButton delButton =(的ImageButton)convertView.findViewById(R.id.delButton);
delButton.setFocusable(真正的);
delButton.setClickable(真正的);
//delButton.setTag(daTag);
delButton.setOnClickListener(新OnClickListener(){//点击监听器来回回删除按钮
@覆盖
公共无效的onClick(视图查看){
dbDel.delRow(); //这是previos code样品删除行的方法
}
});
返回(行);
}
}
和所有这些东西给我的NullPointerException当我点击删除按钮。 我是新来的机器人,并假设我只是错过了一些东西明显。
LogCat中:
ERROR / AndroidRuntime(14027):致命异常:主要
ERROR / AndroidRuntime(14027):显示java.lang.NullPointerException
ERROR / AndroidRuntime(14027):在android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
ERROR / AndroidRuntime(14027):在android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
ERROR / AndroidRuntime(14027):在namespace.DBAdapter.open(DBAdapter.java:66)
ERROR / AndroidRuntime(14027):在namespace.EditEntries.delRow(EditEntries.java:50)
ERROR / AndroidRuntime(14027):在namespace.SMSimpleCursorAdapter $ 1.onClick(SMSimpleCursorAdapter.java:64)
ERROR / AndroidRuntime(14027):在android.view.View.performClick(View.java:2414)
ERROR / AndroidRuntime(14027):在android.view.View $ PerformClick.run(View.java:8838)
ERROR / AndroidRuntime(14027):在android.os.Handler.handleCallback(Handler.java:587)
ERROR / AndroidRuntime(14027):在android.os.Handler.dispatchMessage(Handler.java:92)
ERROR / AndroidRuntime(14027):在android.os.Looper.loop(Looper.java:123)
ERROR / AndroidRuntime(14027):在android.app.ActivityThread.main(ActivityThread.java:4680)
ERROR / AndroidRuntime(14027):在java.lang.reflect.Method.invokeNative(本机方法)
ERROR / AndroidRuntime(14027):在java.lang.reflect.Method.invoke(Method.java:521)
ERROR / AndroidRuntime(14027):在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:858)
ERROR / AndroidRuntime(14027):在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
ERROR / AndroidRuntime(14027):在dalvik.system.NativeStart.main(本机方法)
现在的问题是在你的SMSimpleCursorAdapter code:
EditEntries dbDel =新EditEntries(); //从previous code样品
您创建一个新的对象,但它不会是一个管理活动(如在onCreate方法将不会被调用)。在NPE可能来自你的DBAdapter当您尝试创建它的第二次(从适配器)。
快速修复:
EditEntries dbDel; //从previous code样品
公共SMSimpleCursorAdapter(上下文的背景下,INT布局,光标C,
的String []从,INT []键){
超(背景下,布局,C,从,到);
this.c = C;
this.context =背景;
this.activity =(活动)范围内;
this.dbDel =(EditEntries)范围内;
}
如果你不希望只是一个快速解决以下将是一个更好的解决方案:
- 将在delRow,getEvents方法到您的DBAdapter类
- 修改您的SMSimpleCursorAdapter的构造给了DBAdapter类(在你的ListActivity创建)。
I'm trying to make ListView populated from database, and spice each row with fancy delete button. So I made list Activity and custom SimpleCursorAdapter.
This is main ListView activity:
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
}
}
And this is custom SimpleCursorAdapter:
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);
}
}
And all this stuff gives me NullPointerException when I click delete button. I'm new to android, and suppose that I just missed something obvious.
LogCat:
ERROR/AndroidRuntime(14027): FATAL EXCEPTION: main
ERROR/AndroidRuntime(14027): java.lang.NullPointerException
ERROR/AndroidRuntime(14027): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
ERROR/AndroidRuntime(14027): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
ERROR/AndroidRuntime(14027): at namespace.DBAdapter.open(DBAdapter.java:66)
ERROR/AndroidRuntime(14027): at namespace.EditEntries.delRow(EditEntries.java:50)
ERROR/AndroidRuntime(14027): at namespace.SMSimpleCursorAdapter$1.onClick(SMSimpleCursorAdapter.java:64)
ERROR/AndroidRuntime(14027): at android.view.View.performClick(View.java:2414)
ERROR/AndroidRuntime(14027): at android.view.View$PerformClick.run(View.java:8838)
ERROR/AndroidRuntime(14027): at android.os.Handler.handleCallback(Handler.java:587)
ERROR/AndroidRuntime(14027): at android.os.Handler.dispatchMessage(Handler.java:92)
ERROR/AndroidRuntime(14027): at android.os.Looper.loop(Looper.java:123)
ERROR/AndroidRuntime(14027): at android.app.ActivityThread.main(ActivityThread.java:4680)
ERROR/AndroidRuntime(14027): at java.lang.reflect.Method.invokeNative(Native Method)
ERROR/AndroidRuntime(14027): at java.lang.reflect.Method.invoke(Method.java:521)
ERROR/AndroidRuntime(14027): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
ERROR/AndroidRuntime(14027): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
ERROR/AndroidRuntime(14027): at dalvik.system.NativeStart.main(Native Method)
The problem is in your SMSimpleCursorAdapter code:
EditEntries dbDel = new EditEntries(); //from previous code sample
You create a new object but it won't be a managed Activity (eg. the onCreate method won't be called). The NPE probably comes from your DBAdapter when you try to create it the second time (from your Adapter).
Quick fix:
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;
}
If you don't want just a quick fix the following would be a much better solution:
- Move the delRow, getEvents method into your DBAdapter class
- Modify the constructor of your SMSimpleCursorAdapter to give in the DBAdapter class (created in your ListActivity).
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