No cell service hint during registration.

app/src/main/java/org/thoughtcrime/securesms/registration/fragments/EnterCodeFragment.java

@@ -1,6 +1,8 @@
 package org.thoughtcrime.securesms.registration.fragments;
 
+import android.animation.Animator;
 import android.os.Bundle;
+import android.telephony.PhoneStateListener;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -36,7 +38,9 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
-public final class EnterCodeFragment extends BaseRegistrationFragment {
+public final class EnterCodeFragment extends BaseRegistrationFragment
+                                     implements SignalStrengthPhoneStateListener.Callback
+{
 
   private static final String TAG = Log.tag(EnterCodeFragment.class);
 
@@ -47,8 +51,11 @@ public final class EnterCodeFragment extends BaseRegistrationFragment {
   private CallMeCountDownView     callMeCountDown;
   private View                    wrongNumber;
   private View                    noCodeReceivedHelp;
+  private View                    serviceWarning;
   private boolean                 autoCompleting;
 
+  private PhoneStateListener signalStrengthListener;
+
   @Override
   public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
     return inflater.inflate(R.layout.fragment_registration_enter_code, container, false);
@@ -67,6 +74,9 @@ public final class EnterCodeFragment extends BaseRegistrationFragment {
     callMeCountDown      = view.findViewById(R.id.call_me_count_down);
     wrongNumber          = view.findViewById(R.id.wrong_number);
     noCodeReceivedHelp   = view.findViewById(R.id.no_code);
+    serviceWarning       = view.findViewById(R.id.cell_service_warning);
+
+    signalStrengthListener = new SignalStrengthPhoneStateListener(this, this);
 
     connectKeyboard(verificationCodeView, keyboard);
 
@@ -319,4 +329,40 @@ public final class EnterCodeFragment extends BaseRegistrationFragment {
                                    getString(R.string.RegistrationActivity_code_support_subject),
                                    body);
   }
+
+  @Override
+  public void onNoCellSignalPresent() {
+    if (serviceWarning.getVisibility() == View.VISIBLE) {
+      return;
+    }
+    serviceWarning.setVisibility(View.VISIBLE);
+    serviceWarning.animate()
+                  .alpha(1)
+                  .setListener(null)
+                  .start();
+
+    scrollView.postDelayed(() -> {
+      if (serviceWarning.getVisibility() == View.VISIBLE) {
+        scrollView.smoothScrollTo(0, serviceWarning.getBottom());
+      }
+    }, 1000);
+  }
+
+  @Override
+  public void onCellSignalPresent() {
+    if (serviceWarning.getVisibility() != View.VISIBLE) {
+      return;
+    }
+    serviceWarning.animate()
+                  .alpha(0)
+                  .setListener(new Animator.AnimatorListener() {
+                    @Override public void onAnimationEnd(Animator animation) {
+                      serviceWarning.setVisibility(View.GONE);
+                    }
+                    @Override public void onAnimationStart(Animator animation) {}
+                    @Override public void onAnimationCancel(Animator animation) {}
+                    @Override public void onAnimationRepeat(Animator animation) {}
+                  })
+                  .start();
+  }
 }

app/src/main/java/org/thoughtcrime/securesms/registration/fragments/SignalStrengthPhoneStateListener.java

@@ -0,0 +1,73 @@
+package org.thoughtcrime.securesms.registration.fragments;
+
+import android.content.Context;
+import android.os.Build;
+import android.telephony.PhoneStateListener;
+import android.telephony.SignalStrength;
+import android.telephony.TelephonyManager;
+
+import androidx.annotation.NonNull;
+import androidx.lifecycle.DefaultLifecycleObserver;
+import androidx.lifecycle.LifecycleOwner;
+
+import org.signal.core.util.logging.Log;
+import org.thoughtcrime.securesms.dependencies.ApplicationDependencies;
+import org.thoughtcrime.securesms.util.Debouncer;
+
+final class SignalStrengthPhoneStateListener extends PhoneStateListener
+                                             implements DefaultLifecycleObserver
+{
+  private static final String TAG = Log.tag(SignalStrengthPhoneStateListener.class);
+
+  private final Callback  callback;
+  private final Debouncer debouncer = new Debouncer(1000);
+
+  SignalStrengthPhoneStateListener(@NonNull LifecycleOwner lifecycleOwner, @NonNull Callback callback) {
+    this.callback = callback;
+
+    lifecycleOwner.getLifecycle().addObserver(this);
+  }
+
+  @Override
+  public void onSignalStrengthsChanged(SignalStrength signalStrength) {
+    if (signalStrength == null) return;
+
+    if (isLowLevel(signalStrength)) {
+      Log.w(TAG, "No cell signal detected");
+      debouncer.publish(callback::onNoCellSignalPresent);
+    } else {
+      Log.i(TAG, "Cell signal detected");
+      debouncer.clear();
+      callback.onCellSignalPresent();
+    }
+  }
+
+  private boolean isLowLevel(@NonNull SignalStrength signalStrength) {
+    if (Build.VERSION.SDK_INT >= 23) {
+      return signalStrength.getLevel() == 0;
+    } else {
+      //noinspection deprecation: False lint warning, deprecated by 29, but this else block is for < 23
+      return signalStrength.getGsmSignalStrength() == 0;
+    }
+  }
+
+  interface Callback {
+    void onNoCellSignalPresent();
+
+    void onCellSignalPresent();
+  }
+
+  @Override
+  public void onResume(@NonNull LifecycleOwner owner) {
+    TelephonyManager telephonyManager = (TelephonyManager) ApplicationDependencies.getApplication().getSystemService(Context.TELEPHONY_SERVICE);
+    telephonyManager.listen(this, PhoneStateListener.LISTEN_SIGNAL_STRENGTHS);
+    Log.i(TAG, "Listening to cell phone signal strength changes");
+  }
+
+  @Override
+  public void onPause(@NonNull LifecycleOwner owner) {
+    TelephonyManager telephonyManager = (TelephonyManager) ApplicationDependencies.getApplication().getSystemService(Context.TELEPHONY_SERVICE);
+    telephonyManager.listen(this, PhoneStateListener.LISTEN_NONE);
+    Log.i(TAG, "Stopped listening to cell phone signal strength changes");
+  }
+}

app/src/main/res/drawable/ic_error_outline_14_ultramarine.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="14dp"
+    android:height="14dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+  <path
+      android:fillColor="@color/core_ultramarine"
+      android:pathData="M10.75,6h2.5l-0.5,7.5h-1.5ZM12,2.5A9.5,9.5 0,1 0,21.5 12,9.511 9.511,0 0,0 12,2.5M12,1A11,11 0,1 1,1 12,11 11,0 0,1 12,1ZM13.5,16.5A1.5,1.5 0,1 0,12 18,1.5 1.5,0 0,0 13.5,16.5Z"/>
+</vector>

app/src/main/res/drawable/registration_no_cell_service_warning_border.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+    <corners android:radius="8dp" />
+
+    <solid android:color="@color/core_grey_02" />
+</shape>

app/src/main/res/layout/fragment_registration_enter_code.xml

@@ -88,6 +88,48 @@
                 app:layout_constraintStart_toStartOf="parent"
                 app:layout_constraintTop_toBottomOf="@+id/verify_header" />
 
+            <LinearLayout
+                android:id="@+id/cell_service_warning"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_marginStart="32dp"
+                android:layout_marginTop="8dp"
+                android:layout_marginEnd="32dp"
+                android:alpha="0"
+                android:background="@drawable/registration_no_cell_service_warning_border"
+                android:gravity="center"
+                android:paddingStart="8dp"
+                android:paddingTop="4dp"
+                android:paddingEnd="8dp"
+                android:paddingBottom="4dp"
+                android:text="@string/RegistrationActivity_make_sure_your_phone_has_a_cellular_signal"
+                android:visibility="gone"
+                app:layout_constraintEnd_toEndOf="parent"
+                app:layout_constraintHorizontal_bias="0.5"
+                app:layout_constraintStart_toStartOf="parent"
+                app:layout_constraintTop_toBottomOf="@+id/no_code"
+                tools:alpha="1"
+                tools:visibility="visible">
+
+                <ImageView
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:layout_gravity="top"
+                    android:layout_margin="2dp"
+                    android:background="@drawable/ic_error_outline_14_ultramarine"
+                    android:importantForAccessibility="no" />
+
+                <TextView
+                    style="@style/Signal.Text.Body.Registration"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:text="@string/RegistrationActivity_make_sure_your_phone_has_a_cellular_signal"
+                    android:textAlignment="center"
+                    android:textColor="@color/core_ultramarine"
+                    android:textSize="12sp" />
+
+            </LinearLayout>
+
         </androidx.constraintlayout.widget.ConstraintLayout>
 
     </ScrollView>

app/src/main/res/values/strings.xml

@@ -1509,6 +1509,7 @@
     <string name="RegistrationActivity_enter_your_phone_number_to_get_started">Enter your phone number to get started</string>
     <string name="RegistrationActivity_you_will_receive_a_verification_code">You will receive a verification code. Carrier rates may apply.</string>
     <string name="RegistrationActivity_enter_the_code_we_sent_to_s">Enter the code we sent to %s</string>
+    <string name="RegistrationActivity_make_sure_your_phone_has_a_cellular_signal">Make sure your phone has a cellular signal to receive your SMS or call</string>
 
     <string name="RegistrationActivity_phone_number_description">Phone number</string>
     <string name="RegistrationActivity_country_code_description">Country code</string>