我有一个工作异步任务，我在其中放置了一个进度对话框。问题是当我将进度对话框放入其中时会崩溃：
public class CheckBeerJSON extends AsyncTask
<String, Void, String> {
Context c;
String b;
private ProgressDialog Dialog = new ProgressDialog(c);
public CheckBeerJSON(Context context, String beer)
{
c = context;
b = beer;
}
@Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub
return readJSONFeed(arg0[0]);
}
protected void onPreExecute() {
Dialog.setMessage("Checking your portfolio");
Dialog.setTitle("Searching");
Dialog.show();
}
protected void onPostExecute(String result){
//decode json here
try{
JSONObject json = new JSONObject(result);
String status = json.getString("status");
if(status.equals("no")){
String message = "Beer not logged";
Toast.makeText(c, message, Toast.LENGTH_SHORT).show();
//clear loader image
LinearLayout ll = (LinearLayout) (LinearLayout)((Activity) c).findViewById(R.id.addBeerLayout);
ll.removeAllViews();
//Add beer add button
LayoutInflater mInflater = (LayoutInflater)c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
LinearLayout addButton = (LinearLayout)((Activity) c).findViewById(R.id.addBeerLayout);
addButton.addView(mInflater.inflate(R.layout.addbeerbutton_layout, null));
}
else{
String message = "You have the beer!!";
Toast.makeText(c, message, Toast.LENGTH_SHORT).show();
//clear loader image
LinearLayout ll = (LinearLayout) (LinearLayout)((Activity) c).findViewById(R.id.addBeerLayout);
ll.removeAllViews();
//inflate star rater
LayoutInflater mInflater = (LayoutInflater)c.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
LinearLayout addButton = (LinearLayout)((Activity) c).findViewById(R.id.addBeerLayout);
addButton.addView(mInflater.inflate(R.layout.addrate_layout, null));
RatingBar r = (RatingBar) ((Activity) c).findViewById(R.id.beerRatingBar);
//get user data
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(c);
String userID = prefs.getString("userID", null);
//get beer rating with async task and update rate bar
String url = "my_other_url";
String userURLComp = "u=" + userID;
String beerID = "&b=" + b;
url = url + userURLComp + beerID;
new GetUserRating(c,r).execute(url);
//add listener to bar
addListenerOnRatingBar(c);
}
}
catch(Exception e){
}
Dialog.dismiss();
}
private void addListenerOnRatingBar(Context view) {
RatingBar ratingBar = (RatingBar) ((Activity) view).findViewById(R.id.beerRatingBar);
ratingBar.setOnRatingBarChangeListener(new OnRatingBarChangeListener() {
public void onRatingChanged(RatingBar ratingBar, float rating,
boolean fromUser) {
//next async task to update online database
float stars = ratingBar.getRating();
//get user details
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(c);
String userID = prefs.getString("userID", null);
//get beer id
String beerID = b;
//get rating
String urlRate = "r=" + String.valueOf(ratingBar.getRating());
String urlUserID = "&u=" + userID;
String urlBeerID = "&b=" + beerID;
//construct url
String url2 = "my_url";
url2 = url2 + urlRate + urlUserID + urlBeerID;
Log.d("addRateing", url2);
//async task to update rating in database
new UpdateRating(c).execute(url2);
}
});
}
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();
}
}
我得到的错误是：
08-16 21:22:34.054 10772-10772/com.beerportfolio.beerportfoliopro E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.beerportfolio.beerportfoliopro/com.example.beerportfoliopro.BeerPage}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2332)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2368)
at android.app.ActivityThread.access$600(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1330)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5536)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1074)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:841)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:142)
at android.app.AlertDialog.<init>(AlertDialog.java:98)
at android.app.ProgressDialog.<init>(ProgressDialog.java:77)
at com.example.beerportfoliopro.CheckBeerJSON.<init>(CheckBeerJSON.java:37)
at com.example.beerportfoliopro.BeerPage.onCreate(BeerPage.java:83)
at android.app.Activity.performCreate(Activity.java:5066)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1102)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2288)
... 11 more