如何做Android数据绑定从BaseAdapter for Spinner继承的CustomAdapter？

Question

我在使用带有BaseAdapter的Android DataBinding为Spinner实现CustomAdapter时遇到问题.

数据有两个值.我想使用两个TextView.CustomAdapter必须从BaseAdapter继承,ArrayAdapter的简单变体仅支持一个TextView.从长远来看,第二个TextView可能是一个ImageView,因此将两个值合并为一个String以便能够使用ArrayAdapter仍然无济于事.

我也尝试过:为了确保这个想法和Spinner正常工作,我实现了一个没有DataBinding的版本我在chrislizh项目的https://github.com/chrislizh/SpinnerTwoWayDataBindingDemo上实现了我的数据绑定实现,它正在使用ArrayAdapter.我也尝试调用:binding.executePendingBindings(),并试图不使用ViewHolder模式.

问题导致细节:该项目是关于行星.旋转器允许选择行星.每个行星都有一个名字和一个距离.将显示这两个值.我实现CustomAdapter的结果,名为PlanetAdapter,DataBinding在选择后显示第一个项目两次.查看截图.选择除第一个项目之外的任何其他行星,使用选择"切换"其位置,并继续显示两次.这样,显示的列表中始终缺少一个行星.

PlanetAdapter的代码以及在MainActivty的onCreate方法中创建它的调用:

PlanetAdapter

public class PlanetAdapter extends BaseAdapter
{
    private int itemLayoutResourceId;
    private final List<Planet> planets;
    private LayoutInflater inflater;

    public PlanetAdapter(@NonNull Context context, @LayoutRes int itemLayoutResourceId, List<Planet> planets)
    {
        inflater = LayoutInflater.from(context);
        this.itemLayoutResourceId = itemLayoutResourceId;
        this.planets = planets;
    }

    @Override
    public int getCount()
    {
        return planets.size();
    }

    @Override
    public Object getItem(int position)
    {
        return planets.get(position);
    }

    @Override
    public long getItemId(int position)
    {
        return position;
    }

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

        if (convertView == null) {
            PlanetSpinnerItemBinding itemBinding = DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()), R.layout.planet_spinner_item, parent, false);
            itemBinding.setPlanet(planets.get(position));

            holder = new PlanetViewHolder(itemBinding);
            holder.view = itemBinding.getRoot();
            holder.view.setTag(holder);
        }
        else {
            holder = (PlanetViewHolder) convertView.getTag();
        }
        return holder.view;
    }

    private static class PlanetViewHolder
    {
        private View view;

        PlanetViewHolder(PlanetSpinnerItemBinding binding)
        {
            this.view = binding.getRoot();
        }
    }}

创建和设置适配器:

      public class MainActivity extends AppCompatActivity implements IDataChangeListener
        {
            private static final String BUNDLE_SELECTED_PLANET = "bundle_selected_planet";
            private ActivityMainBinding activityMainBinding_;
            private List<Planet> planets_;

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

            activityMainBinding_ = DataBindingUtil.setContentView(this, R.layout.activity_main);

            planets_ = loadPlanets(this, R.array.planetsInSolarSystem);
            if (planets_ != null) {
                 planets_.add(0, new Planet("", 0));  // insert a blank item on the top of the list

                PlanetAdapter planetAdapter = new PlanetAdapter(this, R.layout.planet_spinner_item, planets_);
                activityMainBinding_.setSpinAdapterPlanet(planetAdapter);
                Planet selectedPlanet = savedInstanceState != null ? savedInstanceState.<Planet>getParcelable(BUNDLE_SELECTED_PLANET) : planets_.get(3);//initial selected planet is Earth, 3 is the index of Earth after a blank item inserted
                activityMainBinding_.setBindingPlanet(new BindingPlanet(this, selectedPlanet));
            }
    } // loadPlanets skipped.
 }

星球类:

public class Planet implements Parcelable {

    private String name_;
    private float distance_; //distance to Sun in AU(Astronomical Unit)

    public Planet(String name, float distance) {
        name_ = name;
        distance_ = distance;
    }

    protected Planet(Parcel in) {
        name_ = in.readString();
        distance_ = in.readFloat();
    }

    public static final Creator<Planet> CREATOR = new Creator<Planet>() {
        @Override
        public Planet createFromParcel(Parcel in) {
            return new Planet(in);
        }

        @Override
        public Planet[] newArray(int size) {
            return new Planet[size];
        }
    };

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(name_);
        dest.writeFloat(distance_);
    }

    @Override
    public String toString() {
        return name_ != null ? name_ : super.toString();
    }

    public String getName() {
        return name_;
    }

    public void setName(String name) {
        name_ = name;
    }

    public float getDistance() {
        return distance_;
    }

    public void setDistance(float distance) {
        distance_ = distance;
    }
}

项目布局的XML:spinner_planet_item.xml`

<data>
    <variable
        name="planet"
        type="au.com.chrisli.spinnertwowaydatabindingdemo.Planet">
    </variable>
</data>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              android:orientation="horizontal"
              android:layout_width="match_parent"
              android:layout_height="match_parent">

    <TextView
        android:id="@+id/planetName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@{planet.name}"
        tools:text="Dummy Planet"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium"/>

    <TextView
        android:id="@+id/planetDistance"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingLeft="8dp"
        android:text="@{String.valueOf(planet.distance)}"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium"
        tools:text="2393.0 km"/>
</LinearLayout>

在github代码中,我还在文件末尾的PlanetAdapter类中包含了经典案例(没有数据绑定),但注释掉了.如果你想看到它的工作原理 - 只需在那里切换getView和PlaneViewHolder实现.

完整的修改项目在我的github上:https://github.com/Minsky/SO_Question_SpinnerDataBindingBaseAdapter

BaseAdapter的Binding实现有什么问题？

Answer 1

正如Commonsware在他的评论中写道的那样,在回收案例中约束观点的方法很缺失.PlanetAdapter中方法getView()的工作代码是这样的:

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

    if (convertView == null) {
        PlanetSpinnerItemBinding itemBinding = DataBindingUtil.inflate(LayoutInflater.from(parent.getContext()), R.layout.planet_spinner_item, parent, false);

        holder = new PlanetViewHolder(itemBinding);
        holder.view = itemBinding.getRoot();
        holder.view.setTag(holder);
    }
    else {
        holder = (PlanetViewHolder) convertView.getTag();
    }
    holder.binding.setPlanet(planets.get(position));
    return holder.view;
}

PlanetViewHolder现在拥有绑定:

private static class PlanetViewHolder {
  private View view;
  private PlanetSpinnerItemBinding binding;

 PlanetViewHolder(PlanetSpinnerItemBinding binding) {
     this.view = binding.getRoot();
     this.binding = binding;
    }
}

最终Github projet在分支"解决":https://github.com/Minsky/SO_Question_SpinnerDataBindingBaseAdapter/tree/solved