Fix ChoosePat/Pin/Pwd crash from async task

Use a retained worker fragment to track the asynchronous
save-and-finish task so that ChoosePattern/Password activity
is properly dismissed after a configuration change.

Bug:23424884
Bug:23521530
Change-Id: I328022c1603cfb0f6812cd8aa7916ae7b72c9950

src/com/android/settings/SaveChosenLockWorkerBase.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2015 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;
+
+import android.app.Fragment;
+import android.content.Intent;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.os.UserHandle;
+
+import com.android.internal.widget.LockPatternUtils;
+
+/**
+ * An invisible retained worker fragment to track the AsyncWork that saves (and optionally
+ * verifies if a challenge is given) the chosen lock credential (pattern/pin/password).
+ */
+abstract class SaveChosenLockWorkerBase extends Fragment {
+
+    private Listener mListener;
+    private boolean mFinished;
+    private Intent mResultData;
+
+    protected LockPatternUtils mUtils;
+    protected boolean mHasChallenge;
+    protected long mChallenge;
+    protected boolean mWasSecureBefore;
+
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setRetainInstance(true);
+    }
+
+    public void setListener(Listener listener) {
+        if (mListener == listener) {
+            return;
+        }
+
+        mListener = listener;
+        if (mFinished && mListener != null) {
+            mListener.onChosenLockSaveFinished(mWasSecureBefore, mResultData);
+        }
+    }
+
+    protected void prepare(LockPatternUtils utils, boolean credentialRequired,
+            boolean hasChallenge, long challenge) {
+        mUtils = utils;
+
+        mHasChallenge = hasChallenge;
+        mChallenge = challenge;
+        mWasSecureBefore = mUtils.isSecure(UserHandle.myUserId());
+
+        mUtils.setCredentialRequiredToDecrypt(credentialRequired);
+
+        mFinished = false;
+        mResultData = null;
+    }
+
+    protected void start() {
+        new Task().execute();
+    }
+
+    /**
+     * Executes the save and verify work in background.
+     * @return Intent with challenge token or null.
+     */
+    protected abstract Intent saveAndVerifyInBackground();
+
+    protected void finish(Intent resultData) {
+        mFinished = true;
+        mResultData = resultData;
+        if (mListener != null) {
+            mListener.onChosenLockSaveFinished(mWasSecureBefore, mResultData);
+        }
+    }
+
+    private class Task extends AsyncTask<Void, Void, Intent> {
+        @Override
+        protected Intent doInBackground(Void... params){
+            return saveAndVerifyInBackground();
+        }
+
+        @Override
+        protected void onPostExecute(Intent resultData) {
+            finish(resultData);
+        }
+    }
+
+    interface Listener {
+        public void onChosenLockSaveFinished(boolean wasSecureBefore, Intent resultData);
+    }
+}