Goal:
Reading a HTML-file using Buffered reader in an AsyncTask on Android.
Problem:
The debug log gives the following error: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference. It gives the error at the onPostExecute void. On further investigation I found out the following code: TVCode.setText(result); is throwing the NullPointerException. This means result = null. I can't find out why result = null since similar code on the normal Java, using Eclipse, is working fine.
Further info:
Android Studio: 1.3.2
JDK: 1.7.0_79-b15 amd64
Permissions:
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
Gradle: minSdkVersion 15, targetSdkVersion 23, compileSdkVersion 23
Here is the code of MainActivity.java:
public class MainActivity extends AppCompatActivity {
public static String ETURL = null;
public static final String TAG = MainActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView TVCode = (TextView) findViewById(R.id.TVCode);
ImageButton BTSend = (ImageButton) findViewById(R.id.BTSend);
final EditText ETURLInput = (EditText) findViewById(R.id.ETUrlInput);
BTSend.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
ETURL = ETURLInput.getText().toString();
new aSync().execute(ETURLInput.getText().toString());
}
}
);
}
private class aSync extends AsyncTask<String, Void, String> {
@Override
protected void onPreExecute() {
}
protected String doInBackground(String... ETURL) {
String line=null;
String result="";
try {
URL url;
url = new URL("" + ETURL);
URLConnection conn = url.openConnection();
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
line=br.readLine();
while (line!= null) {
result=result+line;
line=br.readLine();
}
br.close();
return result;
} catch (Exception e) {
Log.e(TAG, "Error:", e);
}
return result;
}
protected void onPostExecute(String result) {
try {
TextView TVCode = (TextView) findViewById(R.id.TVCode);
TVCode.setText(result);
}
catch (Exception e){
Log.e(TAG, "ERROR: ", e);
}
}
}
Fix:
The TextView must be declared in the onPreExecute method instead of the on onPostExecute method. Thank you all for your help and time.
