传安 ArrayList<customobject> 到接受 ArrayList 作为参数的 function<object> 在 Java<div id="text_translate"><p> 我正在编写一个通用的 java-android function，它将接受ArrayList<Object>作为其参数之一，这样我就可以在我的整个应用程序中使用，而不管 ArrayList 元素的类型如何。</p><p> 这是我的 function：</p><pre> public GenericDisplayAdapter(Activity activity, ArrayList<Object> arrData) { this.m_ArrData = arrData; inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE); }</pre><p> 当我尝试将我的ArrayList<CustomObject>作为参数传递给此 function 时，出现错误“无法从ArrayList<CustomObject>转换为ArrayList<Object> ”，</p><pre> m_LVStructDamageHeader.setAdapter(new GenericDisplayAdapter( (Activity)this, (ArrayList<Object>)arrStructDamageHeaders));</pre><p> 处理这种情况的最佳方法是什么，谢谢</p></div></object></customobject>

Question

I am writing a generic java-android function that will accept as one of it's parameters an ArrayList<Object> , so that I can use all over my application regardless of the type of the ArrayList elements.

This is my function:

public GenericDisplayAdapter(Activity activity, ArrayList<Object> arrData) {

    this.m_ArrData = arrData;
    inflater = (LayoutInflater) activity
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

When I try to to pass my ArrayList<CustomObject> as a parameter to this function, I get the error "can't cast from ArrayList<CustomObject> to ArrayList<Object> ",

        m_LVStructDamageHeader.setAdapter(new GenericDisplayAdapter(
            (Activity)this, (ArrayList<Object>)arrStructDamageHeaders));

What is the best approach to handle such a situation, Thanks

Answer 1

Change your function from

public GenericDisplayAdapter(Activity activity, ArrayList<Object> arrData)

to

public GenericDisplayAdapter(Activity activity, ArrayList<?> arrData)

Then you will be able to pass ArrayList<T> for any T . ArrayList<?> is almost like ArrayList<Object> , but the difference is that while you can add ANY object into the ArrayList<Object> (which is pretty bad if you pass eg ArrayList<CustomObject> there), you cannot add anything into the ArrayList<?> (which is fine).

Answer 2

change the method parameter

ArrayList<Object> to ArrayList<? extends Object>

Answer 3

Consider also, that it may be appropriate to give the GenericDisplayAdapter class a type parameter. Eg

class GenericDisplayAdapter<T> {
    private List<T> m_ArrData;

    public GenericDisplayAdapter(Activity activity, ArrayList<T> arrData) {
        ...
    }
}

So then other methods can take advantage of this type parameter, instead of dealing in Object, they can use T.

Answer 4

You should you generic ArrayList just like

public GenericDisplayAdapter(Activity activity, ArrayList<?> arrData) {

    this.m_ArrData = arrData;
    inflater = (LayoutInflater) activity
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}