Fixed crash if config could not be opened.

src/main/java/com/nutomic/syncthingandroid/activities/MainActivity.java

@@ -71,6 +71,8 @@ public class MainActivity extends SyncthingActivity
                 new Date().getTime() > getFirstStartTime() + USAGE_REPORTING_DIALOG_DELAY &&
                 getApi().getUsageReportAccepted() == RestApi.UsageReportSetting.UNDECIDED) {
             showUsageReportingDialog();
+        } else if (currentState == SyncthingService.State.ERROR) {
+            finish();
         } else if (currentState != SyncthingService.State.ACTIVE && !isFinishing()) {
             if (currentState == SyncthingService.State.DISABLED) {
                 if (mLoadingDialog != null) {

src/main/java/com/nutomic/syncthingandroid/syncthing/SyncthingService.java

@@ -131,7 +131,8 @@ public class SyncthingService extends Service implements
         INIT,
         STARTING,
         ACTIVE,
-        DISABLED
+        DISABLED,
+        ERROR
     }
 
     private State mCurrentState = State.INIT;
@@ -208,14 +209,24 @@ public class SyncthingService extends Service implements
             shutdown();
 
             Log.i(TAG, "Starting syncthing according to current state and preferences");
+            mConfig = null;
+            try {
                 mConfig = new ConfigXml(SyncthingService.this);
+            } catch (ConfigXml.OpenConfigException e) {
+                mCurrentState = State.ERROR;
+                Toast.makeText(this, R.string.config_create_failed, Toast.LENGTH_LONG).show();
+            }
+
+            if (mConfig != null) {
                 mCurrentState = State.STARTING;
                 registerOnWebGuiAvailableListener(mApi);
-            new PollWebGuiAvailableTaskImpl(getFilesDir() + "/" + HTTPS_CERT_FILE).execute(mConfig.getWebGuiUrl());
+                new PollWebGuiAvailableTaskImpl(getFilesDir() + "/" + HTTPS_CERT_FILE)
+                        .execute(mConfig.getWebGuiUrl());
                 mRunnable = new SyncthingRunnable(this, SyncthingRunnable.Command.main);
                 new Thread(mRunnable).start();
                 updateNotification();
             }
+        }
         // Stop syncthing.
         else {
             if (mCurrentState == State.DISABLED)
@@ -305,12 +316,24 @@ public class SyncthingService extends Service implements
 
         @Override
         protected Pair<String, String> doInBackground(Void... voids) {
+            try {
                 mConfig = new ConfigXml(SyncthingService.this);
                 return new Pair<>(mConfig.getWebGuiUrl(), mConfig.getApiKey());
+            } catch (ConfigXml.OpenConfigException e) {
+                return null;
+            }
         }
 
         @Override
         protected void onPostExecute(Pair<String, String> urlAndKey) {
+            if (urlAndKey == null) {
+                Toast.makeText(SyncthingService.this, R.string.config_create_failed,
+                        Toast.LENGTH_LONG).show();
+                mCurrentState = State.ERROR;
+                onApiChange();
+                return;
+            }
+
             mApi = new RestApi(SyncthingService.this, urlAndKey.first, urlAndKey.second,
                     mGuiUser, mGuiPassword,
                     new RestApi.OnApiAvailableListener() {

src/main/java/com/nutomic/syncthingandroid/util/ConfigXml.java

@@ -2,9 +2,12 @@ package com.nutomic.syncthingandroid.util;
 
 import android.content.Context;
 import android.os.Environment;
+import android.os.Handler;
+import android.os.Looper;
 import android.util.Log;
 import android.widget.Toast;
 
+import com.nutomic.syncthingandroid.R;
 import com.nutomic.syncthingandroid.syncthing.SyncthingRunnable;
 
 import org.w3c.dom.Document;
@@ -32,6 +35,9 @@ import javax.xml.transform.stream.StreamResult;
  */
 public class ConfigXml {
 
+    public class OpenConfigException extends RuntimeException {
+    }
+
     private static final String TAG = "ConfigXml";
 
     /**
@@ -41,11 +47,13 @@ public class ConfigXml {
 
     private static final String INVALID_CONFIG_FILE = "config.xml.invalid";
 
+    private static final int OPEN_CONFIG_MAX_TRIES = 10;
+
     private File mConfigFile;
 
     private Document mConfig;
 
-    public ConfigXml(Context context) {
+    public ConfigXml(final Context context) throws OpenConfigException {
         mConfigFile = getConfigFile(context);
         boolean isFirstStart = !mConfigFile.exists();
         if (isFirstStart) {
@@ -53,7 +61,7 @@ public class ConfigXml {
             generateKeysConfig(context);
         }
 
-        for (int i = 0; i < 10 && mConfig == null; i++) {
+        for (int i = 0; i < OPEN_CONFIG_MAX_TRIES && mConfig == null; i++) {
             try {
                 DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
                 mConfig = db.parse(mConfigFile);
@@ -69,9 +77,8 @@ public class ConfigXml {
                 mConfigFile = getConfigFile(context);
             }
         }
-        if (mConfig == null) {
+        if (mConfig == null)
-            Toast.makeText(context, "Failed to create a Syncthing config. Syncthing will not start!", Toast.LENGTH_LONG).show();
+            throw new OpenConfigException();
-        }
 
         if (isFirstStart) {
             changeDefaultFolder();

src/main/res/values/strings.xml

@@ -396,6 +396,9 @@ Please report any problems you encounter via Github.</string>
     <!-- Toast shown if folder observer fails to traverse a folder -->
     <string name="toast_folder_observer_stack_overflow">Directory tree too deep. Check for cyclic symlinks</string>
 
+    <!-- Toast shown if syncthing failed to create a config -->
+    <string name="config_create_failed">Failed to create a Syncthing config. Please check the logs.</string>
+
     <!-- RestApi -->