方法 findViewById(int) 未定义 [英] The method findViewById(int) is undefined
问题描述
我是 Android 开发的新手,我正在尝试编写一个小应用程序,它允许我获取外部 JSON 文件并解析它.我让它工作了,但是如果我尝试在后台作为 AsyncTask
执行它,它将无法工作.Eclipse 给了我错误
I'm new to Android development and I'm trying to code a little app which allows me to grab an external JSON file and parse it. I got this to work, however it wont work if I try to execute it in the background as an AsyncTask
. Eclipse gives me the error
未定义 LongOperation 类型的 findViewById(int) 方法
The method findViewById(int) is undefined for the type LongOperation
在这一行:
TextView txtView1 = (TextView)findViewById(R.id.TextView01);
TextView txtView1 = (TextView)findViewById(R.id.TextView01);
这是我的代码:
public class Main extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new LongOperation().execute();
}
}
class LongOperation extends AsyncTask<String, Void, String> {
private final Context LongOperation = null;
@Override
protected String doInBackground(String... params) {
try {
URL json = new URL("http://www.corps-marchia.de/jsontest.php");
URLConnection tc = json.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
JSONArray ja = new JSONArray(line);
JSONObject jo = (JSONObject) ja.get(0);
TextView txtView1 = (TextView)findViewById(R.id.TextView01);
txtView1.setText(jo.getString("text") + " - " + jo.getString("secondtest"));
}
} catch (MalformedURLException e) {
Toast.makeText(this.LongOperation, "Malformed URL Exception: " + e, Toast.LENGTH_LONG).show();
} catch (IOException e) {
Toast.makeText(this.LongOperation, "IO Exception: " + e, Toast.LENGTH_LONG).show();
} catch (JSONException e) {
Toast.makeText(this.LongOperation, "JSON Exception: " + e, Toast.LENGTH_LONG).show();
}
return null;
}
@Override
protected void onPostExecute(String result) {
}
protected void onPreExecute() {
}
@Override
protected void onProgressUpdate(Void... values) {
ProgressDialog pd = new ProgressDialog(LongOperation);
pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pd.setMessage("Working...");
pd.setIndeterminate(true);
pd.setCancelable(false);
}
}
关于如何解决这个问题有什么想法吗?
Any ideas on how to fix this?
推荐答案
其他答案之一中 AsyncTask
的实现存在缺陷.每次在 publishProgress
中都会创建进度对话框,并且该对话框的引用在方法之外不可见.这是我的尝试:
The implementation of AsyncTask
in one of the other answers is flawed. The progress dialog is being created every time within publishProgress
, and the reference to the dialog is not visible outside the method. Here is my attempt:
public class Main extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new LongOperation().execute();
}
class LongOperation extends AsyncTask<String, Void, String> {
ProgressDialog pd = null;
TextView tv = null;
@Override
protected void onPreExecute(){
tv = Main.this.findViewById(R.id.textvewid);
pd = new ProgressDialog(Main.this);
pd.setMessage("Working...");
// setup rest of progress dialog
}
@Override
protected String doInBackground(String... params) {
//perform existing background task
return result;
}
@Override
protected void onPostExecute(String result){
pd.dismiss();
tv.setText(result);
}
}
}
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