NullPointerException關於在BaseAdapter中填充數據

Question

我正在嘗試使用通過創建活動的意圖傳遞到活動中的數據填充listview 。 您看到的println語句確認數據已正確傳遞（即打印了預期的內容，這意味着適配器中引用的ArrayList已正確初始化）。 但是，我一直在線獲取NullPointerException

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

適配器中肯定有問題-可能在getItem（）中，或者我對cmts.get(position)調用沒有按照我的想法做，但是在這一點上我無法弄清楚。

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

您需要按以下方式在getview方法中訪問textview的內容： convertView.findViewById(R.id.commentText); 這樣訪問它。

  @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 2

將您的適配器的構造函數更改為此（如果它不是您的活動的內部類）：

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

這些行：

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

應該像：

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 3

首先檢查變量是否為null：

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 4

要這樣創建適配器

CommentAdapter ca = new CommentAdapter(cmts);

和CommentAdapter類來創建這樣的構造函數

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

並在CommentAdapter類中創建局部變量

 private ArrayList<Comment> cmts;