如何延长微调，以实现新的功能？ [英] How can I extend spinner to implement a new function?

问题描述

我想在我的code扩展微调的Andr​​oid类来实现一个新的功能，但由于某种原因，这并不工作。

这是扩展的类：

 进口android.content.Context;
进口android.widget.AdapterView;
进口android.widget.Spinner;公共类CustomSpinner扩展微调{    公共CustomSpinner（上下文的背景下）{
        超级（上下文）;
    }    公共无效setSelectionByItemId（适配器视图＆LT;＆GT;父，长ID）{
        的for（int i = 0; I＆LT; parent.getCount（）;我++）{
            长itemIdAtPosition = parent.getItemIdAtPosition（I）
            如果（itemIdAtPosition == ID）{
                parent.setSelection（ⅰ）;
                打破;
            }
        }
    }}
 

这是我在这个实例化类的方式：

  CustomSpinner微调=（CustomSpinner）findViewById（R.id.sphofentries）;
 

这给我一个运行时错误。

这一切都是如果R.id.sphofentries在我的布局作为一个微调声明。

但现在，如果我宣布sphofentries作为一个CustomSpinner我得到一个运行时错误只是在那一刻我的布局设置为活动：

 的setContentView（R.layout.settings）;
 

另外，我pretty肯定，问题是，我需要声明sphofentries作为CustomSpinner，因为如果我这样做：

  CustomSpinner微调=新CustomSpinner（本）;
微调=（CustomSpinner）findViewById（R.id.sphofentries）;
 

这不用问题低谷的第一线，但在第二次则问题不是创建一个新的CustomSpinner但在这CustomSpinner设置sphofentries（这与sphofentries宣布像微调不是CustomSpinner）给出了一个运行时错误

也许我做错事的布局，这是我声明sphofentries作为CustomSpinner方式：

 ＆LT; CustomSpinner
    机器人：ID =@ + ID / sphofentries
    机器人：layout_below =@ + ID / tvhofentries
    机器人：layout_width =300dip
    机器人：layout_height =WRAP_CONTENT
    机器人：重力=CENTER_HORIZONTAL
/＆GT;
 

解决方案

最后还有两个原因不能正常工作，这两个previous的答案是正确的：

1. 这是必要的也是定义与AttributeSet中的参数第二个构造函数。

    公共CustomSpinner（上下文的背景下，ATTRS的AttributeSet）{
       超（背景下，ATTRS）;
    




2. 在微调必须定义为一个CustomSpinner，需要所有的完全限定名声明的布局：

    ＆LT; net.domain.package.CustomSpinner
       机器人：ID =@ + ID / sphofentries
       机器人：layout_below =@ + ID / tvhofentries
       机器人：layout_width =300dip
       机器人：layout_height =WRAP_CONTENT
       机器人：重力=CENTER_HORIZONTAL
   /＆GT;
    

I'm trying to extend Spinner Android class in my code to implement a new function, but for some reason this didn't work.

This is the extended class:

import android.content.Context;
import android.widget.AdapterView;
import android.widget.Spinner;

public class CustomSpinner extends Spinner {

    public CustomSpinner(Context context) {
        super(context);
    }

    public void setSelectionByItemId(AdapterView<?> parent, long id){
        for (int i = 0; i < parent.getCount(); i++) {              
            long itemIdAtPosition = parent.getItemIdAtPosition(i);
            if (itemIdAtPosition == id) {
                parent.setSelection(i);
                break;
            }
        }
    }

}

And this is the way I'm instantiating this class:

CustomSpinner spinner = (CustomSpinner) findViewById(R.id.sphofentries);

This give me an error at runtime.

All this is if R.id.sphofentries is declared in my layout as an spinner.

But now, if I declare sphofentries as a CustomSpinner I get a runtime error just in the moment I set the Layout to the Activity:

setContentView(R.layout.settings);

Also I am pretty sure that the problem is that I need to declare sphofentries as a CustomSpinner because if I do this:

CustomSpinner spinner = new CustomSpinner(this);
spinner = (CustomSpinner) findViewById(R.id.sphofentries);

This goes without problem trough the first line but gives a runtime error in the second then the problem isn't creating a new CustomSpinner but setting the sphofentries in this CustomSpinner (This with sphofentries declared like a Spinner not a CustomSpinner).

Maybe I am doing something wrong in the layout, this is the way I am declaring sphofentries as a CustomSpinner:

<CustomSpinner 
    android:id="@+id/sphofentries"
    android:layout_below="@+id/tvhofentries"
    android:layout_width="300dip"
    android:layout_height="wrap_content"
    android:gravity="center_horizontal"
/>

解决方案

Finally there was two reasons for this to not work properly, the two previous answers are right:

1. It's necessary to define also the second constructor with the AttributeSet parameter.

   public CustomSpinner(Context context, AttributeSet attrs) {
       super(context, attrs);
   

2. In the layout the Spinner must be defined as a CustomSpinner and needs to be declared with all the fully qualified name:

   <net.domain.package.CustomSpinner  
       android:id="@+id/sphofentries" 
       android:layout_below="@+id/tvhofentries"
       android:layout_width="300dip"       
       android:layout_height="wrap_content"
       android:gravity="center_horizontal"
   />
   

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