定製適配器不工作

Question

我有一個定製適配器用於我的ListView。它給我NullPointerException在setAdapter。我經歷了幾次我的代碼，無法弄清楚導致NPE的原因。以下是相關的代碼片段：

活動：

ListView mListView; 
Vector<DashboardBean> dashboardBean= new Vector<DashboardBean>(); 
MyCustomAdapter adapter; 

adapter = new MyCustomAdapter(MyDashboardActivity.this, 
       R.layout.testdashboard_row, dashboardBean); 

     adapter.clear(); 

dashboardBean.add(new DashboardBean(projects, workRequests, status)); 
     mListView.setAdapter(adapter); 

Dashboardbean：

public class DashboardBean { 

    public String project; 
    public String workRequest; 
    public String startDate; 
    public String status; 
    public String actualHours; 
    public String actualMins; 


    public DashboardBean(String project, String workRequest,String status) 
    { 
     this.project = project; 
     this.workRequest = workRequest; 
     this.status = status; 
    } 

} 

CustomAdapter：

public class MyCustomAdapter extends ArrayAdapter<DashboardBean> { 


Context context; 
int layoutResourceId; 
DashboardBean currentMRB; 
Vector<DashboardBean> data; 

public MyCustomAdapter(Context context, int layoutResourceId, Vector<DashboardBean> data) 
{ 
    super(context,layoutResourceId,data); 
    this.layoutResourceId = layoutResourceId; 
    this.context=context; 
    this.data = data; 
} 

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

    View row = convertView; 
    MyStringReaderHolder holder; 


    if(row==null) 
    { 
     LayoutInflater inflater = ((Activity)context).getLayoutInflater(); 
     row = inflater.inflate(layoutResourceId, parent,false); 

     holder= new MyStringReaderHolder(); 


     holder.project = (TextView)row.findViewById(R.id.project); 
     holder.workRequest = (TextView)row.findViewById(R.id.work_request); 
     holder.status = (TextView) row.findViewById(R.id.status); 


     row.setTag(holder); 
    } 
    else 
    { 
     holder=(MyStringReaderHolder) row.getTag(); 
    } 

    DashboardBean mrb = data.elementAt(position); 

    holder.project.setText(mrb.project); 
    holder.workRequest.setText(mrb.workRequest); 
    holder.status.setText(mrb.status); 

    return row; 
} 

static class MyStringReaderHolder 
{ 
TextView project, workRequest, startDate, status, actualHours; 

} 
} 

誰能幫助？

Answer 1

在你的「活動」片段，你從來沒有一個值賦給mListView：

ListView mListView; //initialize me please :) 

正因爲如此，它是空的，並且總是拋出NullPointerException。也許你有一些用xml定義的東西，並且你想要調用findViewById(int)。

mListView = (ListView) findViewById(R.id.theListViewId);