Android 对dragSortListView进行充气时出现NullPointerException

您好，我正在尝试从服务器加载使用bauerca实现的dragSortListView中的图像。我有一个简单的布局，使用和imageview作为拖拽工具。我已经编写了以下代码

import java.util.ArrayList;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.mobeta.android.dslv.DragSortController;
import com.mobeta.android.dslv.DragSortListView;
import com.squareup.picasso.Picasso;

public class MainActivity extends Activity { 
DragSortListView listView;
ReorderAdapter adapter;

private DragSortListView.DropListener onDrop = new DragSortListView.DropListener()
{
    @Override
    public void drop(int from, int to)
    {
        if (from != to)
        {
            Model item = (Model) adapter.getItem(from);
            adapter.list.remove(from);
            adapter.list.add(to, item);
        }
    }
};

private DragSortListView.RemoveListener onRemove = new DragSortListView.RemoveListener()
{
    @Override
    public void remove(int which)
    {
        adapter.list.remove(which);
    }
};

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    listView = (DragSortListView) findViewById(R.id.listview);
    String[] names = new String[]{"http://url1",
            "http://url2","http://url3", "http://url4"};

    ArrayList<Model> list = new ArrayList<Model>();
    for (int i=0; i<names.length; i++) {
        list.add(new Model(names[i], names[i], i));
    }
    adapter = new ReorderAdapter(this, R.layout.item_layout, list);
    listView.setAdapter(adapter);
    listView.setDropListener(onDrop);
    listView.setRemoveListener(onRemove);

    DragSortController controller = new DragSortController(listView);
    controller.setDragHandleId(R.id.menu);
            //controller.setClickRemoveId(R.id.);
    controller.setRemoveEnabled(false);
    controller.setSortEnabled(true);
    controller.setDragInitMode(1);
            //controller.setRemoveMode(removeMode);

    listView.setFloatViewManager(controller);
    listView.setOnTouchListener(controller);
    listView.setDragEnabled(true);
}

private class Model {
    private String text;
    private String url;
    private int position;

    public Model (String text, String url, int position) {
        this.text = text;
        this.url = url;
        this.position = position;
    }

    @Override
    public boolean equals(Object o) {
        if (((Model)o).position == this.position) 
            return true;
        return false;
    }
}
protected DragSortListView getListView() {
    // TODO Auto-generated method stub
    return (DragSortListView) this.findViewById(R.id.listview);
}
private class ReorderAdapter extends BaseAdapter {
    private ArrayList<Model> list;
    Context context;

    public ReorderAdapter(Context context, int resource, ArrayList<Model> objects) {
        this.list = objects;
    }

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

        if (v == null) {
            LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.item_layout, parent, false);
        }  

        ((TextView)v.findViewById(R.id.textView)).setText(list.get(position).text);
        String photo_source=list.get(position).url.toString().replaceAll(" ", "%20");
        try {
            Picasso.with(context).load(photo_source)
            .placeholder(R.drawable.ic_launcher)
            .error(R.drawable.ic_launcher)
            .into(((ImageView)v.findViewById(R.id.menu)));
        } catch(IllegalArgumentException illegalArg){
            illegalArg.printStackTrace();
        } catch(Exception e){
            e.printStackTrace();
        }
        return v;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu)
{
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
}

更改此代码

private class ReorderAdapter extends BaseAdapter {
    private ArrayList<Model> list;
    Context context;

    public ReorderAdapter(Context context, int resource, ArrayList<Model> objects) {
        this.list = objects;
        this.context = context;
    }

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

        if (v == null) {
            LayoutInflater vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            v = vi.inflate(R.layout.item_layout, parent, false);
        }  

        ((TextView)v.findViewById(R.id.textView)).setText(list.get(position).text);
        String photo_source=list.get(position).url.toString().replaceAll(" ", "%20");
        try {
            Picasso.with(context).load(photo_source)
            .placeholder(R.drawable.ic_launcher)
            .error(R.drawable.ic_launcher)
            .into(((ImageView)v.findViewById(R.id.menu)));
        } catch(IllegalArgumentException illegalArg){
            illegalArg.printStackTrace();
        } catch(Exception e){
            e.printStackTrace();
        }
        return v;
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }
}

私有类ReorderaAdapter扩展BaseAdapter{
私有数组列表；
语境；
公共ReorderAdapter（上下文、int资源、ArrayList对象）{
this.list=对象；
this.context=上下文；
}
@凌驾
公共视图getView（int位置、视图转换视图、视图组父视图）{
视图v=转换视图；
如果（v==null）{
LayoutInflater vi=（LayoutInflater）context.getSystemService（context.LAYOUT\u INFLATER\u SERVICE）；
v=vi.充气（R.布局.项目布局，父项，假）；
}  
（（TextView）v.findViewById（R.id.TextView））.setText（list.get（position.text）；
字符串photo_source=list.get（position.url.toString（）.replaceAll（“，“%20”）；
试一试{
毕加索.with（context）.load（照片来源）
.占位符（R.drawable.ic_启动器）
.错误（R.drawable.ic_启动器）
.into（（图像视图）v.findviewbyd（R.id.menu））；
}捕获（IllegalArgumentException illegalArg）{
illegalArg.printStackTrace（）；
}捕获（例外e）{
e、 printStackTrace（）；
}
返回v；
}
@凌驾
public int getCount（）{
//TODO自动生成的方法存根
返回list.size（）；
}
@凌驾
公共对象getItem（int位置）{
//TODO自动生成的方法存根
返回列表。获取（位置）；
}
@凌驾
公共长getItemId（int位置）{
//TODO自动生成的方法存根
返回位置；
}
}

试试这种方法，希望这能帮助您解决问题。

第一件事是NPE的出现是因为您没有初始化上下文对象，您使用它来膨胀布局，并使用毕加索加载图像，所以在构造函数中初始化上下文对象：

this.context= context;

第二件事是，无论何时使用自定义适配器，都要尝试使用模式

它总是关于NPE lol

this.context= context;

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    Viewholder holder;
    if (convertView == null) {
        holder = new Viewholder();
        convertView  = LayoutInflater.from(context).inflate(R.layout.item_layout, null);
        holder.textView = (TextView) convertView.findViewById(R.id.textView);
        holder.menu = (TextView) convertView.findViewById(R.id.menu);

        convertView.setTag(holder);
    }else{
        holder =(Viewholder) convertView.getTag();
    }


    holder.textView.setText(list.get(position).text);
    try {
          Picasso.with(context).load(list.get(position).url.toString().replaceAll(" ", "%20")).placeholder(R.drawable.ic_launcher).error(R.drawable.ic_launcher).into(holder.menu);
    } catch(IllegalArgumentException illegalArg){
         illegalArg.printStackTrace();
    } catch(Exception e){
         e.printStackTrace();
    }
   return convertView;
}

class Viewholder {
  TextView textView;
  ImageView menu;
}