如何为嵌套片段实现自定义适配器

Question

我正在尝试在嵌套片段中创建一个列表视图，该片段将作为元素图像保存，其下方带有标题，尽管我在创建用于填充列表视图的自定义适配器中不断收到空指针错误。这是代码：

自定义适配器：

import android.app.Activity;
import android.view.View;
        import android.content.Context;
        import android.view.LayoutInflater;
        import android.view.View;
        import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
        import android.widget.ImageView;
        import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class ImageAdapter extends ArrayAdapter<Image> {

    ArrayList<Image> imageList;
    private Context mContext;
    int resource;

    public ImageAdapter(Context context, int resource, ArrayList<Image> imageObjects) {
        super(context, resource, imageObjects);
        this.imageList = imageObjects;
        this.mContext = context;
        this.resource = resource;
    }

    public ArrayList<Image> getImageList() {
        return imageList;
    }

    public void setImageList(ArrayList<Image> imageList) {
        this.imageList = imageList;
    }

    public Context getmContext() {
        return mContext;
    }

    public void setmContext(Context mContext) {
        this.mContext = mContext;
    }

    public int getResource() {
        return resource;
    }

    public void setResource(int resource) {
        this.resource = resource;
    }

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

        if(convertView==null){
            LayoutInflater layoutInflater = (LayoutInflater) getContext().getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
            convertView = layoutInflater.inflate(R.layout.fragment_membership, null, true);

        }

        Image image = getItem(position);

        ImageView layoutImage = (ImageView)convertView.findViewById(R.id.membershipimage);
        layoutImage.setImageResource(image.getImageResourceID());
        TextView layoutText = (TextView)convertView.findViewById(R.id.membershipCaption);
        layoutText.setText(image.getImageCaption());

        return super.getView(position, convertView, parent);
    }
}

我使用的片段，在另一个片段中：

import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.GridView;
import android.widget.ListView;

import java.util.ArrayList;

public class MembershipFragment extends Fragment {

    ArrayList<Image> imageList;
    ListView membershipListView;

    public static MembershipFragment newInstance() {
        MembershipFragment fragment = new MembershipFragment();
        return fragment;
    }

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

    }



    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_membership, container, false);

        return view;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        imageList = new ArrayList<>();
        for(int i=0; i<3; i++){
            Image image = new Image(R.drawable.cinnamon_apple_breakfast, "Test Caption");
            imageList.add(image);
        }
        membershipListView = (ListView)view.findViewById(R.id.membershipListView);
        try{
            ImageAdapter adapter = new ImageAdapter(getContext(), R.layout.list_view_item, imageList);
            membershipListView.setAdapter(adapter);
        }
        catch (Exception e){
            e.printStackTrace();
        }
    }
}

当我尝试将图像资源 id 设置为 imageview 时，应用程序在启动时不断崩溃，在 getView 方法中的自定义适配器中抛出空指针异常。问题出在哪里？

Answer 1

我认为你混淆了你的布局。

你应该在这里使用getActivity。

ImageAdapter adapter = new ImageAdapter(getContext(), R.layout.list_view_item

你在那里传递了那个布局资源。但是在适配器内部，您使用的是不同的布局。

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

    if(convertView==null){
        LayoutInflater layoutInflater = (LayoutInflater) getContext().getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        convertView = layoutInflater.inflate(R.layout.fragment_membership, null, true);

    }

你做了一个getResource 方法，我猜是有原因的？你永远不会调用它。

我认为您不希望您的片段布局包含片段布局列表（因为递归）

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_membership, container, false);

    return view;
}