使用毕加索在列表视图中加载图像

Question

请看一下，我有一个片段，设置一个适配器，从 firebase 数据库中获取字符串 url 值，但没有图像加载。

我的片段：

public class PromoFragment extends Fragment {


private DatabaseReference mDatabase;

List<Promo> promoList = new ArrayList<>();
ListView listViewPromo;

public PromoFragment() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mDatabase = FirebaseDatabase.getInstance().getReference();

}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment

    View view = inflater.inflate(R.layout.fragment_promo, container, false);
    listViewPromo = (ListView) view.findViewById(R.id.listViewPromo);
    listenPromo();  //here i load my data, i currently have 3 childs, each child has imageUrl
    PromoAdapter promoAdapter = new PromoAdapter(getActivity().getApplicationContext(), R.layout.list_promo, promoList);
    listViewPromo.setAdapter(promoAdapter);
    return view;
}


private void listenPromo() {

    mDatabase.child("Promo").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // Get Post object and use the values to update the UI
            // MainActivity.currUser = dataSnapshot.getValue(User.class);

            for (DataSnapshot dsp : dataSnapshot.getChildren()) {
                promoList.add(dsp.getValue(Promo.class)); //add result into array list

            }

            // ...
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            // Getting User Class data failed...
            Log.w("Canceled", "loadUserData:onCancelled", databaseError.toException());
            // ...

        }


    });
}

}

我的fragment_promo.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".PromoFragment">

    <ListView
        android:id="@+id/listViewPromo"
        android:layout_height="wrap_content"
        android:layout_width="match_parent">
    </ListView>

</RelativeLayout>

list_promo.xml

 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <ImageView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/imageViewPromo" />

</LinearLayout>

promo.java class

每个 object 我有 3 个变量，但我只会在这种情况下使用 durl（url 下载）。

public class Promo {
private String durl;
private Boolean active;
private String timestamp;


public Promo() {  //default constructor

}

public Promo(String durl, Boolean active, String timestamp) {
    this.durl = durl;
    this.active = active;
    this.timestamp = timestamp;
}

public String getDurl() {
    return durl;
}

public void setDurl(String durl) {
    this.durl = durl;
}

public Boolean getActive() {
    return active;
}

public void setActive(Boolean active) {
    this.active = active;
}

public String getTimestamp() {
    return timestamp;
}

public void setTimestamp(String timestamp) {
    this.timestamp = timestamp;
}

}

PromoAdapter.java class

public class PromoAdapter extends ArrayAdapter<Promo> {

Context context;
List<Promo> myList;

public PromoAdapter(Context context, int resource, List<Promo> objects) {
    super(context, resource, objects);

    this.context = context;
    this.myList = objects;
}


@Override
public int getCount() {
    if(myList != null)
        return myList.size();
    return 0;
}

@Override
public Promo getItem(int position) {
    if(myList != null)
        return myList.get(position);
    return null;
}

@Override
public long getItemId(int position) {
    if(myList != null)
        return myList.get(position).hashCode();
    return 0;

}


@Override
public View getView(int position, View convertView, ViewGroup parent) {

    Holder holder;


    if (convertView == null){

        //we need a new holder to hold the structure of the cell
        holder = new Holder();

        //get the XML inflation service
        LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        convertView = inflater.inflate(R.layout.list_promo, null);

        holder.imageView = (ImageView)convertView.findViewById(R.id.imageViewPromo);

        convertView.setTag(holder);

    }else{
        holder = (Holder)convertView.getTag();

    }     
    Promo promo = getItem(position); 
    Picasso.with(context)
            .load(promo.getDurl())
            .placeholder(R.drawable.coin25)
            .error(R.drawable.hnbspic)
            .into(holder.imageView);

    return convertView;
}


private class Holder{

    ImageView imageView;

}

我尝试过的：

检查浏览器中的图片url是否有效
listenPromo 也成功地获取了所有 children 图像 url（我之前测试过它以在使用 picasso 之前从数据库中获取数据）
将load(promo.getDurl())更改为load(uri.parse(promo.getDurl()))
添加占位符和错误图片，也没有图片出现。我的片段是空白的。

请帮忙..如果代码正常，那么它应该显示 3 张图片。

感谢您的关注。

Answer 1

请使用此代码：

   Transformation blurTransformation = new Transformation() {
            @Override
            public Bitmap transform(Bitmap source) {
                Bitmap blurred = Blur.fastblur(context, source, 15);
                source.recycle();
                return blurred;
            }

            @Override
            public String key() {
                return "blur()";
            }
        };

     Picasso.with(context)

                    .load(R.drawable.coin25)
                    // thumbnail url goes here
                    .placeholder(R.drawable.coin25)
                    .transform(blurTransformation)
                    .memoryPolicy(MemoryPolicy.NO_CACHE, MemoryPolicy.NO_STORE)
                    .into(holder.imageView, new Callback() {
                        @Override
                        public void onSuccess() {
                            Picasso.with(context)
                                    .load(promo.getDurl()) // image url goes here
                                    .fit()
                                    .centerCrop()

                                    .error(R.drawable.hnbspic)
                                    .placeholder(holder.imageView.getDrawable())
                                    .fit()
                                    .into(holder.imageView);

                        }

                        @Override
                        public void onError() {
                        }
                    });

试试这个。如果这对 you.then 不起作用，请告诉我

Answer 2

添加promoAdapter.notifyDataSetChanged()；在 onDataChange 中，它将为您工作。

mDatabase.child("Promo").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // Get Post object and use the values to update the UI
        // MainActivity.currUser = dataSnapshot.getValue(User.class);

        for (DataSnapshot dsp : dataSnapshot.getChildren()) {
            promoList.add(dsp.getValue(Promo.class)); //add result into array list

        }
         promoAdapter.notifyDataSetChanged();

        // ...
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        // Getting User Class data failed...
        Log.w("Canceled", "loadUserData:onCancelled", databaseError.toException());
        // ...

    }




 });

addValueEventListener 在后台工作，所以它会先设置 Adater，然后你得到你的 response.so 只是通知适配器将为你工作。

Answer 3

根据您的代码，适配器不一定传递列表项。我敦促您使 适配器全局声明 并在 onDataChange[ 上检测到任何更改时添加 adapter.notifyDataSetChanged() =15=].

使用毕加索在列表视图中加载图像

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