如何使用 ArrayList 动态更新微调器? [英] How do I dynamically update a spinner using ArrayList?
问题描述
我创建了一个 Spinner
,它填充了一个 ArrayList
.我想动态地向 ArrayList
添加值,所以 Spinner
动态填充.但是,当我尝试向 ArrayList
添加值时,我得到一个 NullPointerException
.
I have created a Spinner
that is populated with an ArrayList
. I want to dynamically add values to the ArrayList
, so the the Spinner
populates dynamically. However, when I try to add values to my ArrayList
, I get a NullPointerException
.
我错过了什么?在修改 ArrayList
之前是否必须重置适配器?
What am I missing? Do I have to reset the adapter before amending the ArrayList
?
这是我的代码:
我的微调器、数组列表和适配器:
My spinner, arraylist, and adapter:
deleteselection = (Spinner)view.findViewById(R.id.deletespinner);
portfoliosdelete = new ArrayList<String>();
portfoliosdelete.add("Select Portfolio");
adapterdeletetype = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item,portfoliosdelete){
@Override
public View getDropDownView(int position, View convertView, ViewGroup parent)
{
View v = null;
// If this is the initial dummy entry, make it hidden
if (position == 0) {
TextView tv = new TextView(getContext());
tv.setHeight(0);
tv.setVisibility(View.GONE);
v = tv;
}
else {
// Pass convertView as null to prevent reuse of special case views
v = super.getDropDownView(position, null, parent);
}
// Hide scroll bar because it appears sometimes unnecessarily, this does not prevent scrolling
parent.setVerticalScrollBarEnabled(false);
return v;
}
};
adapterdeletetype.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
deleteselection.setAdapter(adapterdeletetype);
我动态更新微调器的代码:
My code to dynamically update spinner:
else if(users.contains(usernull)){
pn1 = enterportfolioname.getText().toString();
user1 = new PortfolioRecord(pn1, "someemail@gmail.com");
users.remove(usernull);
users.add(user1);
portfoliosdelete.add(pn1); // <-- This causes a null pointer exception
adapterdeletetype.notifyDataSetChanged();
portfoliolist.invalidateViews();
推荐答案
使用下面的代码.当用户从微调器中选择并添加新项目时,此代码将添加一个新项目.
Use the code below. This code will add a new item when the user selects and add a new item from the spinner.
代码示例:
布局 main.xml:
layout main.xml:
<?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"
android:orientation="vertical"
android:weightSum="10" >
<Spinner
android:id="@+id/cmbNames"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
布局 spinner_item.xml
layout spinner_item.xml
<?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"
android:orientation="vertical" >
<TextView
android:id="@+id/tvName"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
活动类:
public class MainActivity extends Activity {
private static final String NAME = "name";
private static final String ADD_NEW_ITEM = "Add New Item";
private SimpleAdapter adapter;
private Spinner cmbNames;
private List<HashMap<String, String>> lstNames;
private int counter;
private OnItemSelectedListener itemSelectedListener = new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
HashMap<String, String> map = lstNames.get(arg2);
String name = map.get(NAME);
if (name.equalsIgnoreCase(ADD_NEW_ITEM)) {
lstNames.remove(map);
counter++;
addNewName(String.valueOf(counter));
addNewName(ADD_NEW_ITEM);
adapter.notifyDataSetChanged();
}
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
populateList();
cmbNames = (Spinner) findViewById(R.id.cmbNames);
adapter = new SimpleAdapter(this, lstNames, R.layout.spinner_item,
new String[] { NAME }, new int[] { R.id.tvName });
cmbNames.setAdapter(adapter);
cmbNames.setOnItemSelectedListener(itemSelectedListener);
}
private void populateList() {
lstNames = new ArrayList<HashMap<String, String>>();
addNewName("abc");
addNewName("pqr");
addNewName("xyz");
addNewName(ADD_NEW_ITEM);
}
private void addNewName(String name) {
HashMap<String, String> map = new HashMap<String, String>();
map.put(NAME, name);
lstNames.add(map);
}
}
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