Question

我正在尝试构建一个填充列表视图的异步任务。当我尝试使用findViewBYId设置listView时使用：

ListView lv = (ListView) ((View) c).findViewById(R.id.tastelist);

我收到此错误：

Cannot cast from Context to View

我的整个异步任务类是：

public class GetTasteJSON extends AsyncTask
<String, Void, String> {

    Context c;

    public GetTasteJSON(Context context)
    {
         c = context;
    }

    @Override
    protected String doInBackground(String... arg0) {
        // TODO Auto-generated method stub
        return readJSONFeed(arg0[0]);
    }

    protected void onPostExecute(String result){

        //decode json here
        try{

            JSONObject json = new JSONObject(result);

            //acces listview
            ListView lv = (ListView) ((View) c).findViewById(R.id.tastelist);

            //make array list for beer
            final List<BeerData> beerList = new ArrayList<BeerData>();

        }
        catch(Exception e){

        }

    }

    public String readJSONFeed(String URL) {
        StringBuilder stringBuilder = new StringBuilder();
        HttpClient httpClient = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(URL);
        try {
            HttpResponse response = httpClient.execute(httpGet);
            StatusLine statusLine = response.getStatusLine();
            int statusCode = statusLine.getStatusCode();
            if (statusCode == 200) {
                HttpEntity entity = response.getEntity();
                InputStream inputStream = entity.getContent();
                BufferedReader reader = new BufferedReader(
                        new InputStreamReader(inputStream));
                String line;
                while ((line = reader.readLine()) != null) {
                    stringBuilder.append(line);
                }
                inputStream.close();
            } else {
                Log.d("JSON", "Failed to download file");
            }
        } catch (Exception e) {
            Log.d("readJSONFeed", e.getLocalizedMessage());
        }        
        return stringBuilder.toString();
    }

}

Answer 1

将转换更改为

ListView lv = (ListView) ((Activity) c).findViewById(R.id.tastelist);

本案例中的上下文应该是您的活动

Answer 2

调用findViewById和activity（在本例中是上下文）和View（我相信你试图这样做）之间存在差异。如果您为了启动活动而夸大的视图是您想要获取的视图的父视图，您可能希望尝试强制转换为您的活动，而不是视图。否则，尝试创建ViewGroup类型的实例变量，并使用setter传入父视图。

Answer 3

上下文必须是您的活动，因此将其投射到您的活动中，而不是像您那样投射到视图...

如果您有List活动，您只需这样做：

ListView lv=((ListActivity) context).getListView();

无法从我的asynctask访问我的列表视图

3 个答案: