Clickable ListView | 易学教程

问题

I'm looking now a few days for a solution for clickable items in a listView.

First I came across this: developer.android.com/resources/articles/touch-mode.html and found that it's doesn't have the "normal" onListItemClick() behavouir.

Then I came across of this code: http://www.androidsnippets.org/snippets/125/

// LINE 296-321

    @Override  
    protected ViewHolder createHolder(View v) {  
        // createHolder will be called only as long, as the ListView is not filled  
        // entirely. That is, where we gain our performance:  
        // We use the relatively costly findViewById() methods and  
        // bind the view's reference to the holder objects.  
        TextView text = (TextView) v.findViewById(R.id.listitem_text);  
        ImageView icon = (ImageView) v.findViewById(R.id.listitem_icon);  
        ViewHolder mvh = new MyViewHolder(text, icon);  

        // Additionally, we make some icons clickable  
        // Mind, that item becomes clickable, when adding a click listener (see API)  
        // so, it is not necessary to use the android:clickable attribute in XML  
        icon.setOnClickListener(new ClickableListAdapter.OnClickListener(mvh) {  

            public void onClick(View v, ViewHolder viewHolder) {  
                // we toggle the enabled state and also switch the icon  
                MyViewHolder mvh = (MyViewHolder) viewHolder;  
                MyData mo = (MyData) mvh.data;  
                mo.enable = !mo.enable; // toggle  
                ImageView icon = (ImageView) v;  
                icon.setImageBitmap(  
                        mo.enable ? ClickableListItemActivity.this.mIconEnabled  
                                : ClickableListItemActivity.this.mIconDisabled);  
            }  
        });

While debugging I noticed the parameter View v is a TextView and not a "normal" View and then of course:

TextView text = (TextView) v.findViewById(R.id.listitem_text);

returnes null and I get a NullPointerException...

Any ideas why? And how I can solve this?

Thanks in advance! :)

回答1:

How do you create your instance of ClickableListAdapter ?

When you create your list adapter, you have to pass a resource id viewId, this should be a layout which will be inflated later.

public ClickableListAdapter(Context context, int viewid, List objects) {  

        // Cache the LayoutInflate to avoid asking for a new one each time.  
        mInflater = LayoutInflater.from(context);  
        mDataObjects = objects;  
        mViewId = viewid;

Below, the code inflate the xml layout passed to the constructor and call createHolder.

view = mInflater.inflate(mViewId, null);  
// call the user's implementation  
holder = createHolder(view);

So make sure that when instantiating your ClickableListAdapter, you pass a layout instead of an id

Edit You have to create a xml layout with the following which is taken from the link you have provided:

<?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="wrap_content"  
  android:orientation="horizontal"  
  android:gravity="center_vertical"  
  >  

<TextView android:text="Text" android:id="@+id/listitem_text"  
            android:layout_weight="1"   
            android:layout_width="fill_parent"   
            android:layout_height="wrap_content"  
            ></TextView>  
<ImageView android:id="@+id/listitem_icon"  
            android:src="@drawable/globe2_32x32"  
            android:layout_width="wrap_content"   
            android:layout_height="wrap_content"  
            android:maxWidth="32px"  
            android:maxHeight="32px"  
            >  
</ImageView>  
</LinearLayout>

If you call it mylistrow.xml in the layout directory, so you construct your adapter as :

adapter = new MyClickableChannelListAdapter(this, R.layout.mylistrow, channelList); 
setListAdapter(adapter);

回答2:

List items should be clickable right out of the box. You can check how lists are coded by looking at ApiDemos project code. It should be present on your local machine since it is a part of the SDK. I have it at <root_sdk_folder>\platforms\android-2.0.1\samples\ApiDemos.

来源：https://stackoverflow.com/questions/4578390/clickable-listview

标签

java

android

listview

nullpointerexception