Android 为什么不能从 ArrayAdapter 添加/删除项目？
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Why can't one add/remove items from an ArrayAdapter?
提问by mmo
I am using an ArrayAdapter<CharSequence>to populate the items to list in a android.widget.Spinner. That works all fine.
我正在使用ArrayAdapter<CharSequence>来填充要在android.widget.Spinner. 这一切正常。
But now I want to keep the list of items dynamic, i.e. I want to be able to add/remove items from the selection list at runtime. However, when I call adapter.add(item)or adapter.remove(item)I always get a UnsupportedOperationException, even though the Javadocs of the ArrayAdapterclass describe these two methods as to be usable for exactly that intended purpose.
但现在我想保持项目列表的动态，即我希望能够在运行时从选择列表中添加/删除项目。然而，当我调用adapter.add(item)或adapter.remove(item)我总是得到一个UnsupportedOperationException，即使ArrayAdapter该类的Javadocs将这两种方法描述为完全可以用于预期目的。
Is this a bug, really not implemented or what am I missing here?
这是一个错误，真的没有实现还是我在这里遗漏了什么？
回答by CommonsWare
You probably initialized the adapter with a plain Java array (e.g., String[]). Try using something that implements the java.util.Listinterface (e.g., ArrayList<String>).
您可能使用普通的 Java 数组（例如，String[]）初始化了适配器。尝试使用实现java.util.List接口的东西（例如，ArrayList<String>）。
回答by zeratul021
I know it's late but just a quick explanation: it's because method Arrays.asList(T... array) returns custom inner class named ArrayListthat is read-only. As already said, you need to provide full impl. e.g. java.util.ArrayList.
我知道这已经晚了，但只是一个简单的解释：这是因为方法 Arrays.asList(T... array) 返回名为ArrayList 的自定义内部类，它是只读的。如前所述，您需要提供完整的实现。例如 java.util.ArrayList。
回答by benvd
Here's the source code of ArrayAdapter#remove:
这里的源代码ArrayAdapter#remove：
public void remove(T object) {
if (mOriginalValues != null) {
synchronized (mLock) {
mOriginalValues.remove(object);
}
} else {
mObjects.remove(object);
}
if (mNotifyOnChange) notifyDataSetChanged();
}
The only thing that can throw an UnsupportedOperationExceptionthere is the line in the else-block. So the problem is that the list you're using doesn't support removing items. My guess is you're using an array. Try an ArrayList, for instance.
唯一可以抛出UnsupportedOperationExceptionthere 的是 else 块中的行。所以问题是您使用的列表不支持删除项目。我的猜测是你正在使用一个数组。例如，尝试使用 ArrayList。
edit: So yeah, what Mark said...
编辑：所以是的，马克所说的......
回答by user1063503
I was having the same problem, my data was saved in resource String Array, so I was creating ArraAdapter with createFromResource.
The following code for creating ArrayAdapter from resource String Array solved the problem:
我遇到了同样的问题，我的数据保存在资源字符串数组中，所以我用createFromResource创建了ArraAdapter。
下面从资源字符串数组创建ArrayAdapter的代码解决了这个问题：
Resources res = getResources();
String[] cities = res.getStringArray(R.array.cities_array);
ArrayAdapter<CharSequence> adapter = new ArrayAdapter(
this,
android.R.layout.simple_spinner_item,
new ArrayList(Arrays.asList(cities)));
回答by Tom
In your adapter Class - Delete an Item
在您的适配器类中 - 删除一个项目
remove(position);
notifyDataSetChanged();
Add an Item -
添加项目 -
adapter.add (newItem);
adapter.notifyDataSetChanged ();
回答by Prince Bhardwaj
Probably, you are using List in your ArrayAdapterclass instead of ArrayList.
可能，您在ArrayAdapter类中使用 List而不是ArrayList。
Try converting your array or list to ArrayList-
尝试将您的数组或列表转换为ArrayList-
new ArrayList<ClassType>(Arrays.asList(array));
