Implement modifier keys settings UI.

Add four modifier keys and one reset button.

Bug: 244535460
Test: local test
Change-Id: I45822b0d8391022c17439dc25ab86fe022e9f43f

src/com/android/settings/inputmethod/ModifierKeysPreferenceController.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright (C) 2022 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.inputmethod;
+
+import android.content.Context;
+
+import androidx.fragment.app.DialogFragment;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentManager;
+import androidx.preference.Preference;
+import androidx.preference.PreferenceScreen;
+
+import com.android.settings.core.BasePreferenceController;
+
+public class ModifierKeysPreferenceController extends BasePreferenceController {
+
+    private static String KEY_TAG = "modifier_keys_dialog_tag";
+    private static String KEY_RESTORE_PREFERENCE = "modifier_keys_restore";
+
+    private Fragment mParent;
+    private FragmentManager mFragmentManager;
+
+    public ModifierKeysPreferenceController(Context context, String key) {
+        super(context, key);
+    }
+
+    public void setFragment(Fragment parent) {
+        mParent = parent;
+    }
+
+    @Override
+    public void displayPreference(PreferenceScreen screen) {
+        super.displayPreference(screen);
+        // TODO: getModifierKeyRemapping()
+        // setTitle
+        // setSummary
+        if (mParent == null) {
+            return;
+        }
+        // The dialog screen depends on the previous selected key's fragment.
+        // In the rotation scenario, we should remove the previous dialog screen first.
+        clearPreviousDialog();
+    }
+
+    @Override
+    public boolean handlePreferenceTreeClick(Preference preference) {
+        if (preference.getKey().equals(KEY_RESTORE_PREFERENCE)) {
+            return false;
+        }
+        showModifierKeysDialog(preference);
+        return true;
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return AVAILABLE;
+    }
+
+    private void showModifierKeysDialog(Preference preference) {
+        ModifierKeysPickerDialogFragment fragment =
+                new ModifierKeysPickerDialogFragment(preference);
+        fragment.setTargetFragment(mParent, 0);
+        fragment.show(mFragmentManager, KEY_TAG);
+    }
+
+    private void clearPreviousDialog() {
+        mFragmentManager = mParent.getFragmentManager();
+        DialogFragment preKeysDialogFragment =
+                (DialogFragment) mFragmentManager.findFragmentByTag(KEY_TAG);
+        if (preKeysDialogFragment != null) {
+            preKeysDialogFragment.dismiss();
+        }
+    }
+}