我正在处理笔记应用程序。我已经实现了一个note类来显示列表项和Note Serializable。我想在显示警告对话框后从上下文菜单中删除单个列表视图项。现在我正在崩溃，不知道自己做错了什么。
主要活动
public boolean onContextItemSelected(final MenuItem item) {
final AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
final Note mLoadedNote = (Note) mListNotes.getAdapter().getItem(info.position);
mLoadedNote.getTitle();
switch (item.getItemId()) {
case R.id.delete:
AlertDialog.Builder alertDialog = new AlertDialog.Builder(this)
.setTitle("Delete " + mLoadedNote.getTitle())
.setMessage("are you sure?")
.setPositiveButton("YES", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
// here is where am getting the error
if(mLoadedNote != null) {
ArrayAdapter<String> note = (ArrayAdapter<String>) mListNotes.getAdapter().getItem(info.position);
note.remove(note.getItem(info.position));
note.notifyDataSetChanged();
Toast.makeText(MainActivity.this, mLoadedNote.getTitle() + " is deleted", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MainActivity.this, "can not delete the note '" + mLoadedNote.getTitle() + "'", Toast.LENGTH_SHORT).show();
}
}
})
.setNegativeButton("NO", null); //do nothing on clicking NO button :P
alertDialog.show();
}
return super.onContextItemSelected(item);
}
注意适配器
public class NoteAdapter extends ArrayAdapter<Note> {
public static final int WRAP_CONTENT_LENGTH = 50;
public NoteAdapter(Context context, int resource, List<Note> objects) {
super(context, resource, objects);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null) {
convertView = LayoutInflater.from(getContext())
.inflate(R.layout.view_note_item, null);
}
Note note = getItem(position);
if(note != null) {
TextView title = (TextView) convertView.findViewById(R.id.list_note_title);
TextView date = (TextView) convertView.findViewById(R.id.list_note_date);
TextView content = (TextView) convertView.findViewById(R.id.list_note_content_preview);
title.setText(note.getTitle());
date.setText(note.getDateTimeFormatted(getContext()));
//correctly show preview of the content (not more than 50 char or more than one line!)
int toWrap = WRAP_CONTENT_LENGTH;
int lineBreakIndex = note.getContent().indexOf('\n');
//not an elegant series of if statements...needs to be cleaned up!
if(note.getContent().length() > WRAP_CONTENT_LENGTH || lineBreakIndex < WRAP_CONTENT_LENGTH) {
if(lineBreakIndex < WRAP_CONTENT_LENGTH) {
toWrap = lineBreakIndex;
}
if(toWrap > 0) {
content.setText(note.getContent().substring(0, toWrap) + "...");
} else {
content.setText(note.getContent());
}
} else { //if less than 50 chars...leave it as is :P
content.setText(note.getContent());
}
}
return convertView;
}
}
Note.java
public class Note implements Serializable {
private long mDateTime; //creation time of the note
private String mTitle; //title of the note
private String mContent; //content of the note
public Note(long dateInMillis, String title, String content) {
mDateTime = dateInMillis;
mTitle = title;
mContent = content;
}
public void setDateTime(long dateTime) {
mDateTime = dateTime;
}
public void setTitle(String title) {
mTitle = title;
}
public void setContent(String content) {
mContent = content;
}
public long getDateTime() {
return mDateTime;
}
/**
* Get date time as a formatted string
* @param context The context is used to convert the string to user set locale
* @return String containing the date and time of the creation of the note
*/
public String getDateTimeFormatted(Context context) {
SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss"
, context.getResources().getConfiguration().locale);
formatter.setTimeZone(TimeZone.getDefault());
return formatter.format(new Date(mDateTime));
}
public String getTitle() {
return mTitle;
}
public String getContent() {
return mContent;
}
}
错误
FATAL EXCEPTION: main
Process: com.app.ben.notetaker, PID: 27476
java.lang.ClassCastException: com.app.ben.notetaker.Note cannot be cast to android.widget.ArrayAdapter
at com.app.ben.notetaker.MainActivity$2.onClick(MainActivity.java:103)
at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:161)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
答案 0 :(得分：0)
改变这个：
ArrayAdapter<String> note = (ArrayAdapter<String>) mListNotes.getAdapter().getItem(info.position);
到此：
ArrayAdapter<Note> note = (ArrayAdapter<Note>) mListNotes.getAdapter();
另外，使用note作为ArrayAdater var的名称并不好。将其重命名为notesArrayAdapter或类似内容。