API не работает и progressBar продолжает вращаться

Question

Я новичок, и я пытаюсь узнать, как использовать API на Android. Я использую приложение для биткойнов, чтобы узнать API. Но у меня есть несколько проблем. Я создал индикатор прогресса и цену TextView в mainactivity.xml. Я установил видимость progressbar и textview невидимым по умолчанию. Моя мысль очень проста, я создал новый класс AsyncTask, и после того, как все будет сделано, я установлю индикатор прогресса невидимым и текстовое представление, видимое в onPostExecute(), чтобы показать цену. Но это не сработало. Индикатор прогресса продолжает вращаться, он не показывает цену, я не понимаю, почему она не работает.

The API i am using

MainActivity

import android.os.AsyncTask; 

import android.os.Bundle; 

import android.support.v7.app.AppCompatActivity; 

import android.util.Log; 

import android.view.View; 
import android.widget.ProgressBar; 
import android.widget.TextView; 


import org.json.JSONObject; 
import org.json.JSONTokener; 

import java.net.URL; 
import java.net.HttpURLConnection; 
import java.io.InputStreamReader; 
import java.io.BufferedReader; 


public class MainActivity extends AppCompatActivity { 


     public static String line; 
     public static ProgressBar progressBar; 

     static String API_URL="https://api.coindesk.com/v1/bpi/currentprice/try.json"; 

     static TextView priceTextView; 
     static TextView timeTextView; 

     static int priceInt; 




      @Override 
      protected void onCreate(Bundle savedInstanceState) { 

       super.onCreate(savedInstanceState); 


       setContentView(R.layout.activity_main); 



       priceTextView=(TextView)findViewById(R.id.priceText); 
       timeTextView=(TextView)findViewById(R.id.timeText); 

       progressBar=(ProgressBar)findViewById(R.id.progressBar); 


       retrievePriceTask retrievePriceTask=new retrievePriceTask(); 
       retrievePriceTask.execute(); 



      } 




     } 



    class retrievePriceTask extends AsyncTask <Void,Void,String>{ 




     @Override 
     protected void onPreExecute() { 
      MainActivity.progressBar.setVisibility(View.VISIBLE); 
      MainActivity.priceTextView.setVisibility(View.INVISIBLE); 


     } 

     @Override 
     protected String doInBackground(Void... urls) { 

      try { 
       URL url = new URL(MainActivity.API_URL); 
       HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection(); 
       try { 
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream())); 
        StringBuilder stringBuilder = new StringBuilder(); 

        while ((MainActivity.line = bufferedReader.readLine()) != null) { 
         stringBuilder.append(MainActivity.line).append("\n"); 
        } 
        bufferedReader.close(); 
        return stringBuilder.toString(); 


       } 
       finally{ 
        urlConnection.disconnect(); 
       } 
      } 
      catch(Exception e) { 
       Log.e("ERROR", e.getMessage(), e); 
       return null; 
      } 
     } 





     @Override 
     protected void onPostExecute(String s) { 



      MainActivity.priceTextView.setVisibility(View.VISIBLE); 
      MainActivity.progressBar.setVisibility(View.INVISIBLE); 


      try{ 
       JSONObject jsonObject=(JSONObject)new JSONTokener(MainActivity.line).nextValue(); 
       MainActivity.priceInt=jsonObject.getJSONObject("bpi").getJSONObject("TRY").getInt("rate"); 

       MainActivity.priceTextView.setText(MainActivity.priceInt); 
      } 
      catch (Exception e){ 
       e.printStackTrace(); 
      } 


     } 
    } 

Мой Logcat

07-16 10:20:08.884 2269-2269/zaaa.trinki E/AndroidRuntime: FATAL EXCEPTION: main 
                  Process: zaaa.trinki, PID: 2269 
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{zaaa.trinki/zaaa.trinki.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference 
                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
                   at android.app.ActivityThread.access$800(ActivityThread.java:144) 
                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
                   at android.os.Handler.dispatchMessage(Handler.java:102) 
                   at android.os.Looper.loop(Looper.java:135) 
                   at android.app.ActivityThread.main(ActivityThread.java:5221) 
                   at java.lang.reflect.Method.invoke(Native Method) 
                   at java.lang.reflect.Method.invoke(Method.java:372) 
                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
                  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setVisibility(int)' on a null object reference 
                   at zaaa.trinki.retrievePriceTask.onPreExecute(MainActivity.java:94) 
                   at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587) 
                   at android.os.AsyncTask.execute(AsyncTask.java:535) 
                   at zaaa.trinki.MainActivity.onCreate(MainActivity.java:55) 
                   at android.app.Activity.performCreate(Activity.java:5933) 
                   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 
                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251) 
                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)  
                   at android.app.ActivityThread.access$800(ActivityThread.java:144)  
                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)  
                   at android.os.Handler.dispatchMessage(Handler.java:102)  
                   at android.os.Looper.loop(Looper.java:135)  
                   at android.app.ActivityThread.main(ActivityThread.java:5221)  
                   at java.lang.reflect.Method.invoke(Native Method)  
                   at java.lang.reflect.Method.invoke(Method.java:372)  
                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)  
                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)  
07-16 10:37:42.062 16262-16262/zaaa.trinki E/AndroidRuntime: FATAL EXCEPTION: main 
                  Process: zaaa.trinki, PID: 16262 
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{zaaa.trinki/zaaa.trinki.MainActivity}: android.content.res.Resources$NotFoundException: String resource ID #0x0 
                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) 
                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) 
                   at android.app.ActivityThread.access$800(ActivityThread.java:144) 
                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
                   at android.os.Handler.dispatchMessage(Handler.java:102) 
                   at android.os.Looper.loop(Looper.java:135) 
                   at android.app.ActivityThread.main(ActivityThread.java:5221) 
                   at java.lang.reflect.Method.invoke(Native Method) 
                   at java.lang.reflect.Method.invoke(Method.java:372) 
                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) 
                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 
                   Caused by: android.content.res.Resources$NotFoundException: String resource ID #0x0 
                   at android.content.res.Resources.getText(Resources.java:274) 
                   at android.support.v7.widget.ResourcesWrapper.getText(ResourcesWrapper.java:52) 
                   at android.widget.TextView.setText(TextView.java:4122) 
                   at zaaa.trinki.MainActivity.onCreate(MainActivity.java:63) 
                   at android.app.Activity.performCreate(Activity.java:5933) 
                   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 
                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251) 
                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)  
                   at android.app.ActivityThread.access$800(ActivityThread.java:144)  
                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)  
                   at android.os.Handler.dispatchMessage(Handler.java:102)  
                   at android.os.Looper.loop(Looper.java:135)  
                   at android.app.ActivityThread.main(ActivityThread.java:5221)  
                   at java.lang.reflect.Method.invoke(Native Method)  
                   at java.lang.reflect.Method.invoke(Method.java:372)  
                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)  
                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)  

Answer 1

Используйте ProgressDialog вместо ProgressBar:

ProgressDialog myProgressDialog = ProgressDialog.show(Context CONTEXT, String TITLE, String MESSAGE, boolean INDETERMINATE, boolean CANCELABLE); 

myProgressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER); 

в nd в вашем onPostExecute() просто поместите myProgressDialog.dismiss()