add: about page, settings, notification switch

app/src/main/java/com/stardust/scriptdroid/tool/BackPressedHandler.java

@@ -0,0 +1,40 @@
+package com.stardust.scriptdroid.tool;
+
+import android.app.Activity;
+import android.widget.Toast;
+
+import com.stardust.scriptdroid.R;
+
+/**
+ * Created by Stardust on 2017/2/3.
+ */
+public interface BackPressedHandler {
+
+    void onBackPressed();
+
+    class DoublePressExit implements BackPressedHandler {
+
+        private final Activity mActivity;
+        private long mLastPressedMillis;
+        private long mDoublePressInterval = 1000;
+
+        public DoublePressExit(Activity activity) {
+            mActivity = activity;
+        }
+
+        public DoublePressExit setDoublePressInterval(long doublePressInterval) {
+            mDoublePressInterval = doublePressInterval;
+            return this;
+        }
+
+        @Override
+        public void onBackPressed() {
+            if (System.currentTimeMillis() - mLastPressedMillis < mDoublePressInterval) {
+                mActivity.finish();
+            } else {
+                mLastPressedMillis = System.currentTimeMillis();
+                Toast.makeText(mActivity, R.string.text_press_again_to_exit, Toast.LENGTH_SHORT).show();
+            }
+        }
+    }
+}