NullPointerException在填充BaseAdapter中的数据时

Question

我试图填充listview，数据通过创建它的意图传递给活动。您看到的println声明确认数据正确传递（即打印了预期内容，这意味着适配器中引用的ArrayList已正确初始化）。不过，我一直就行了

content.setText(Html.fromHtml(cmts.get(position).content)); 

一定有什么东西错在适配器得到一个NullPointerException - 也许在getItem（）时，或许我对cmts.get(position)电话是不是做我觉得是，但在这一点上，我无法弄清楚。

public class CommentsView extends Activity { 
ArrayList<Comment> cmts; 

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

    cmts = (ArrayList<Comment>) getIntent().getExtras().getSerializable("clist"); 

    for (Comment c : cmts) { 
     System.out.println("CMTinCV: " + c.content); 
    } 

    ListView lv = (ListView)findViewById(R.id.commentsList); 

    CommentAdapter ca = new CommentAdapter(); 

    lv.setAdapter(ca); 

} 

class CommentAdapter extends BaseAdapter { 
    public CommentAdapter(){ 

    } 
@Override 
public int getCount() { 
    return cmts.size()-1; 
} 

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

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

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

    if (convertView == null) { 
     convertView = getLayoutInflater().inflate(R.layout.commentbox, null); 

     TextView content = (TextView)findViewById(R.id.commentText); 
     TextView author = (TextView)findViewById(R.id.commentAuthor);    
     TextView date = (TextView)findViewById(R.id.commentDate);  

     content.setText(Html.fromHtml(cmts.get(position).content)); 
     author.setText(cmts.get(position).author.name); 
     date.setText(cmts.get(position).date); 
    } 

    return convertView; 
} 

} 
} 

Answer 1

适配器的构造函数改成这样（如果它不是为您的活动的内部类）：

ArrayList<Comment> cmts; 
public CommentAdapter(ArrayList<Comment> mComments){ 
    this.cmts = mComments; 
} 

和这些行：

TextView content = (TextView)findViewById(R.id.commentText); 
TextView author = (TextView)findViewById(R.id.commentAuthor);    
TextView date = (TextView)findViewById(R.id.commentDate); 

应该是这样的：

TextView content = (TextView) convertView.findViewById(R.id.commentText); 
TextView author = (TextView) convertView.findViewById(R.id.commentAuthor);    
TextView date = (TextView) convertView.findViewById(R.id.commentDate); 

Answer 2

检查变量为空或不是第一：

if(cmts.get(position) != null) { 
    content.setText(Html.fromHtml(cmts.get(position).content)); 
    author.setText(cmts.get(position).author.name); 
    date.setText(cmts.get(position).date); 
} 

Answer 3

您需要访问的TextView在下面的getview方法： convertView.findViewById(R.id.commentText);访问它像这样。

@Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
    if (convertView == null) { 
    convertView = getLayoutInflater().inflate(R.layout.commentbox, null); 

    TextView content = (TextView)convertView.findViewById(R.id.commentText); 
    TextView author = (TextView)convertView.findViewById(R.id.commentAuthor);    
    TextView date = (TextView)convertView.findViewById(R.id.commentDate);  

    content.setText(Html.fromHtml(cmts.get(position).content)); 
    author.setText(cmts.get(position).author.name); 
    date.setText(cmts.get(position).date); 
} 
    return convertView; 
} 

Answer 4

要创建这样

CommentAdapter ca = new CommentAdapter(cmts); 

而且CommentAdapter类适配器这样

public CommentAdapter(ArrayList<Comment> cmts){ 
     this.cmts = cmts; 
} 

创建构造函数，并在CommentAdapter类中创建局部变量

private ArrayList<Comment> cmts;