自定义列表视图上的毕加索

Question

我是 android 的初学者，我正在尝试将 google 个位置 API 中的图像用于我的自定义列表视图。我正在尝试使用毕加索来做到这一点。我可以毫无问题地获取文本，但是当我尝试从 url 附加图像时，它给了我一个 "Target must not be null" 错误。任何 comments/help/suggestions 表示赞赏。

我的自定义列表行 places_layout.xml:

     <?xml version="1.0" encoding="utf-8"?>
     <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:orientation="horizontal"
      android:weightSum="1">
            <ImageView
            android:id="@+id/placeicon"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="0.10"/>
            <TextView
            android:id="@+id/placeinfo"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:drawablePadding="20dp"
            android:layout_centerVertical="true"
            android:layout_toRightOf="@+id/placeicon"
            android:layout_toEndOf="@+id/placeicon" />
     </RelativeLayout>

我的异步后执行代码：

    ImageView places_icon = (ImageView) findViewById(R.id.placeicon);

    venuesfound = (ArrayList) parsedataFound(result);
            ArrayList<String> venuesList = new ArrayList<>();
            for(int i = 0; i<venuesfound.size();i++){
                if(venuesfound.get(i).getImageURL() != null){
                    Picasso.with(getApplicationContext())
                            .load(venuesfound.get(i).getImageURL())
                            .into(places_icon);
                }
                venuesList.add(venuesfound.get(i).getName()
                        + "\nOpen: " + venuesfound.get(i).getOpenNow()
                        + "\n(" + venuesfound.get(i).getCategory() + ")");
            }
            placesList = (ListView) findViewById(R.id.places_list);
            placesAdapter = new ArrayAdapter(DisplayPlacesActivity.this, R.layout.places_layout, R.id.placeinfo, venuesList);
            placesList.setAdapter(placesAdapter);

Logcat:

     java.lang.IllegalArgumentException: Target must not be null.
        at com.squareup.picasso.RequestCreator.into(RequestCreator.java:618)
        at com.squareup.picasso.RequestCreator.into(RequestCreator.java:601)
        at com.example.johnchy.samplegui.DisplayPlacesActivity$dataRequest.onPostExecute(DisplayPlacesActivity.java:102)
        at com.example.johnchy.samplegui.DisplayPlacesActivity$dataRequest.onPostExecute(DisplayPlacesActivity.java:56)
        at android.os.AsyncTask.finish(AsyncTask.java:631)
        at android.os.AsyncTask.access0(AsyncTask.java:177)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5419)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
        at dalvik.system.NativeStart.main(Native Method)

再次感谢任何帮助！

Answer 1

问题是，您尝试将图像附加到 ImageView，但还不存在。由于您想在列表中显示图像，因此需要将附件移动到适配器中，因为这是您创建新 ImageView 的地方。为此，您需要创建一个新的 ArrayAdapter：

public class PicassoAdapter extends ArrayAdapter<String> {
    public PicassoAdapter(List<String> urls, Context context){
        super(context, 0, urls);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        PlaceViewHolder holder;
        //ListView tries to reuse invisible Row-Views to save memory, thats why this method can be called with null OR actually a ready View
        if(convertView == null){
            //in this case we need to create a new View
            //create a holder Object that we will attach to the view
            holder = new PlaceViewHolder();
            //in this line we actually create a new row from the xml-file
            convertView = View.inflate(getContext(), R.layout.places_layout, parent, false);
            //we attach the Image- and Text-View to our holder, so we can access them in the next step
            holder.placeIcon = (ImageView)convertView.findViewById(R.id.placeicon);
            holder.placeInfo = (TextView)convertView.findViewById(R.id.placeinfo);
            convertView.setTag(holder)
        } else {
            //if the view is already created, simply get the holder-object
            holder = (PlaceViewHolder)convertView.getTag();
        }
        //I assume the URL is a String, if you need another Type, simply change it here and in class declaration
        String url = getItem(position);
        Picasso.with(getContext())
                        .load(url)
                        //now we have an ImageView, that we can use as target
                        .into(holder.placeIcon);
         //you can set the info here
         holder.placeInfo.setText("test");
         }
    }

    //we need this class as holder object
    public static class PlaceViewHolder {
        private ImageView placeIcon;
        private TextView palceInfo;
    }
}

现在您可以在列表中使用此适配器：

placesList.setAdapter(new PicassoAdapter(urls, DisplayPlacesActivity.this));

请注意，这段代码的性能可能很差，因为我们尝试在 UI-Thread 上加载图像，但我认为作为示例没问题

自定义列表视图上的毕加索

Picasso on custom listview

java

android

listview

imageview

picasso