毕加索对自定义列表视图

Question

我是一个初学者与Android，我试图从谷歌地方API使用图像到我的自定义列表视图。我试图用毕加索来做到这一点。我可以让文本没有问题，但是当我试图从URL附加图像时，它给了我一个“目标不能为空”的错误。任何意见/帮助/建议表示赞赏。

我定制listrow 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PostExecute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); 

的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.access$600(AsyncTask.java:177) 
     at android.os.AsyncTask$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) 

同样，任何帮助表示赞赏！

Answer 1

问题是，您尝试将图像附加到ImageView，那还没有。由于您想要在列表中显示图像，因此您需要将附件移动到适配器中，因为这是您创建新的ImageView的地方。您将需要创建一个新的ArrayAdapter用于此目的：

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; 
    } 
} 

现在你可以在你的列表中使用该适配器：

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

提防，此代码的性能可能会很糟糕，因为我们尝试在UI线程上加载图像，但我认为它可以作为示例