Support to share Wi-Fi hotspot via QR code

1. QR code scanner (Wi-Fi Easy Connect) does not support sharing Wi-Fi hotspot
   at current stage
2. Wi-Fi hotspot QR code button only shows when Wi-Fi hotspot is enabled
3. The QR code has the security string "WPA" for hotspot's WPA2_PSK

Bug: 123151660
Test: atest WifiTetherSSIDPreferenceControllerTest
            WifiQrCodeTest WifiDppConfiguratorActivityTest
            WifiDppEnrolleeActivityTest
            WifiDppQrCodeGeneratorFragmentTest
            WifiDppQrCodeScannerFragmentTest
            WifiNetworkListFragmentTest
            WifiDppChooseSavedWifiNetworkFragmentTest

Change-Id: I2e89450180b82cc841ee3b15be52bfc6f9f6164d

src/com/android/settings/wifi/tether/WifiTetherSsidPreference.java

@@ -0,0 +1,115 @@
+/*
+ * 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.wifi.tether;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.graphics.drawable.Drawable;
+import android.util.AttributeSet;
+import android.util.Log;
+import android.view.View;
+import android.widget.ImageButton;
+
+import androidx.annotation.DrawableRes;
+import androidx.preference.PreferenceViewHolder;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.settings.R;
+import com.android.settings.widget.ValidatedEditTextPreference;
+
+/**
+ * Support a QR code share button for {@code EditTextPreference} that supports input validation.
+ */
+public class WifiTetherSsidPreference extends ValidatedEditTextPreference {
+    private static final String TAG = "WifiTetherSsidPreference";
+
+    private ImageButton mImageButton;
+    private Drawable mButtonIcon;
+    private View.OnClickListener mClickListener;
+    private boolean mVisible;
+
+    public WifiTetherSsidPreference(Context context, AttributeSet attrs,
+            int defStyleAttr, int defStyleRes) {
+        super(context, attrs, defStyleAttr, defStyleRes);
+
+        initialize();
+    }
+
+    public WifiTetherSsidPreference(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+
+        initialize();
+    }
+
+    public WifiTetherSsidPreference(Context context, AttributeSet attrs) {
+        super(context, attrs);
+
+        initialize();
+    }
+
+    public WifiTetherSsidPreference(Context context) {
+        super(context);
+
+        initialize();
+    }
+
+    private void initialize() {
+        setWidgetLayoutResource(R.layout.wifi_button_preference_widget);
+    }
+
+    @Override
+    public void onBindViewHolder(PreferenceViewHolder holder) {
+        super.onBindViewHolder(holder);
+
+        if (mImageButton == null) {
+            mImageButton = (ImageButton) holder.findViewById(R.id.button_icon);
+
+            mImageButton.setContentDescription(
+                    getContext().getString(R.string.wifi_dpp_share_hotspot));
+            setButtonIcon(R.drawable.ic_qrcode_24dp);
+            mImageButton.setImageDrawable(mButtonIcon);
+        }
+
+        if (mVisible) {
+            mImageButton.setOnClickListener(mClickListener);
+            mImageButton.setVisibility(View.VISIBLE);
+        } else {
+            mImageButton.setVisibility(View.GONE);
+        }
+    }
+
+    public void setButtonOnClickListener(View.OnClickListener listener) {
+        mClickListener = listener;
+    }
+
+    public void setButtonVisible(boolean visible) {
+        mVisible = visible;
+    }
+
+    private void setButtonIcon(@DrawableRes int iconResId) {
+        try {
+            mButtonIcon = getContext().getDrawable(iconResId);
+        } catch (Resources.NotFoundException exception) {
+            Log.e(TAG, "Resource does not exist: " + iconResId);
+        }
+    }
+
+    @VisibleForTesting
+    boolean isQrCodeButtonAvailable() {
+        return mVisible && mClickListener != null;
+    }
+}