我是初学者，创建一个带有复选框的列表视图。当我检查一些复选框并返回时，当我回到相同的活动时，复选框会被取消选中。意味着他们失去了他们的状态。所以我试图将他们的状态保存在数据库中。但是我得到了 ClassCastException 异常。那么如何实现呢？请帮忙，我的代码是，
public View getView(final int position, View convertView,
ViewGroup parent) {
// Event to display
final Even eventzz = (Even) this.getItem(position);
// The child views in each row.
final CheckBox checkBox;
TextView textView;
// Create a new row view
if (convertView == null) {
convertView = inflater.inflate(R.layout.eventsinfo, null);
// Find the child views.
textView = (TextView) convertView
.findViewById(R.id.rowTextView);
checkBox = (CheckBox) convertView.findViewById(R.id.CheckBox01);
checkBox.setBackgroundColor(Color.TRANSPARENT);
// Optimization: Tag the row with it's child views, so we don't
// have to call findViewById() later when we reuse the row.
convertView.setTag(new EventViewHolder(textView, checkBox));
checkBox.setOnCheckedChangeListener(new OnCheckedChangeListener() {
@Override
public void onCheckedChanged(CompoundButton buttonView,
boolean isChecked) {
int realPosition = (Integer) buttonView.getTag();
if (isChecked) {
itemChecked.set(realPosition, true);
// update the database to store the new checked item:
ContentValues cv = new ContentValues();
cv.put("list_position", realPosition);
statusDb.insert("status", null, cv);
} else {
itemChecked.set(realPosition, false);
// delete this position from the database because it was
// unchecked
statusDb.delete("status", "list_position = "
+ realPosition, null);
}
}
});
checkBox.setChecked(itemChecked.get(position));
// If CheckBox is toggled, update the event it is tagged with.
checkBox.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
int realPosition = (Integer) checkBox.getTag();
CheckBox cb = (CheckBox) v;
Even eventz = (Even) cb.getTag();
eventz.setChecked(cb.isChecked());
else {
// Because we use a ViewHolder, we avoid having to call
// findViewById().
EventViewHolder viewHolder = (EventViewHolder) convertView
.getTag();
checkBox = viewHolder.getCheckBox();
textView = viewHolder.getTextView();
}
checkBox.setTag(new Integer(position));
checkBox.setChecked(itemChecked.get(position));
// Tag the CheckBox with the Event it is displaying, so that we can
// access the event in onClick() when the CheckBox is toggled.
checkBox.setTag(eventzz);
// Display events data
checkBox.setChecked(eventzz.isChecked());
textView.setText(eventzz.getName());
return convertView;
}
助手.java
class Helper extends SQLiteOpenHelper {
public Helper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
// the list_position will hold the position from the list that are
// currently checked
String sql = "CREATE TABLE status (list_position INTEGER);";
db.execSQL(sql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Just for interface
}
}
MainActivity.java
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.eventstoremindlist);
// Find the ListView resource.
mainListView = (ListView) findViewById(R.id.mainListView);
checkBox = (CheckBox) findViewById(R.id.CheckBox01);
ArrayList<Even> eventList = new ArrayList<Even>();
eventList.addAll(Arrays.asList(events));
// Set our custom array adapter as the ListView's adapter.
listAdapter = new EventArrayAdapter(this, eventList, null);
// Retrieve the list of position that are checked(if any) from the
// database
statusDb = mHelper.getWritableDatabase();
Cursor statusCursor = statusDb.rawQuery("SELECT * FROM status", null);
int[] savedStatus = null;
if ((statusCursor != null) & (statusCursor.moveToFirst())) {
savedStatus = new int[statusCursor.getCount()];
int i = 0;
do {
savedStatus[i] = statusCursor.getInt(0);
i++;
} while (statusCursor.moveToNext());
}
// if the cursor is null or empty we just pass the null savedStatus to
// the adapter constructor and let it handle(setting all the CheckBoxes
// to unchecked)
mainListView.setAdapter(listAdapter);
例外是，
10-07 13:07:15.922: E/AndroidRuntime(816): FATAL EXCEPTION: main
10-07 13:07:15.922: E/AndroidRuntime(816): java.lang.ClassCastException: com.kalnirnay.kalnirnay.EventsToRemindActivity$Even
10-07 13:07:15.922: E/AndroidRuntime(816): at com.kalnirnay.kalnirnay.EventsToRemindActivity$EventArrayAdapter$1.onCheckedChanged(EventsToRemindActivity.java:264)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.widget.CompoundButton.setChecked(CompoundButton.java:124)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.widget.CompoundButton.toggle(CompoundButton.java:86)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.widget.CompoundButton.performClick(CompoundButton.java:98)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.view.View$PerformClick.run(View.java:9080)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.os.Handler.handleCallback(Handler.java:587)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.os.Handler.dispatchMessage(Handler.java:92)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.os.Looper.loop(Looper.java:123)
10-07 13:07:15.922: E/AndroidRuntime(816): at android.app.ActivityThread.main(ActivityThread.java:3683)
10-07 13:07:15.922: E/AndroidRuntime(816): at java.lang.reflect.Method.invokeNative(Native Method)
10-07 13:07:15.922: E/AndroidRuntime(816): at java.lang.reflect.Method.invoke(Method.java:507)
10-07 13:07:15.922: E/AndroidRuntime(816): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-07 13:07:15.922: E/AndroidRuntime(816): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-07 13:07:15.922: E/AndroidRuntime(816): at dalvik.system.NativeStart.main(Native Method)