Add Secure NFC functionality

Secure NFC will permit NFC acitvity only when screen
is unlocked.

Bug: 117253725
Test: Manual; Toggle switch; check if HCE works with screen off
Change-Id: I9977d85065fc7ebca3ed4991ffa52fef0590cf90

src/com/android/settings/nfc/SecureNfcEnabler.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.nfc;
+
+import android.content.Context;
+import android.nfc.NfcAdapter;
+import android.provider.Settings;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.SwitchPreference;
+
+import com.android.settings.R;
+
+/**
+ * SecureNfcEnabler is a helper to manage the Secure Nfc on/off checkbox preference
+ * It turns on/off Secure NFC and ensures the summary of the preference reflects
+ * the current state.
+ */
+public class SecureNfcEnabler extends BaseNfcEnabler {
+    private final SwitchPreference mPreference;
+
+    public SecureNfcEnabler(Context context, SwitchPreference preference) {
+        super(context);
+        mPreference = preference;
+    }
+
+    @Override
+    protected void handleNfcStateChanged(int newState) {
+        switch (newState) {
+            case NfcAdapter.STATE_OFF:
+                mPreference.setSummary(R.string.nfc_disabled_summary);
+                mPreference.setEnabled(false);
+                break;
+            case NfcAdapter.STATE_ON:
+                mPreference.setChecked(mPreference.isEnabled());
+                mPreference.setEnabled(true);
+                break;
+            case NfcAdapter.STATE_TURNING_ON:
+                mPreference.setEnabled(false);
+                break;
+            case NfcAdapter.STATE_TURNING_OFF:
+                mPreference.setEnabled(false);
+                break;
+        }
+    }
+}