NullPointerException在填充BaseAdapter中的數據時

Question

我試圖填充listview，數據通過創建它的意圖傳遞給活動。您看到的println聲明確認數據正確傳遞（即打印了預期內容，這意味着適配器中引用的ArrayList已正確初始化）。不過，我一直就行了

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

一定有什麼東西錯在適配器得到一個NullPointerException - 也許在getItem（）時，或許我對cmts.get(position)電話是不是做我覺得是，但在這一點上，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

適配器的構造函數改成這樣（如果它不是爲您的活動的內部類）：

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

和這些行：

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

應該是這樣的：

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

檢查變量爲空或不是第一：

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

您需要訪問的TextView在下面的getview方法： convertView.findViewById(R.id.commentText);訪問它像這樣。

@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

要創建這樣

CommentAdapter ca = new CommentAdapter(cmts); 

而且CommentAdapter類適配器這樣

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

創建構造函數，並在CommentAdapter類中創建局部變量

private ArrayList<Comment> cmts;