Add: Sample Script Tab, EMCAScript Guide

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

@@ -5,12 +5,15 @@ import android.widget.Toast;
 
 import com.stardust.scriptdroid.R;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * Created by Stardust on 2017/2/3.
  */
 public interface BackPressedHandler {
 
-    void onBackPressed();
+    boolean onBackPressed();
 
     class DoublePressExit implements BackPressedHandler {
 
@@ -28,13 +31,33 @@ public interface BackPressedHandler {
         }
 
         @Override
-        public void onBackPressed() {
+        public boolean 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();
             }
+            return true;
+        }
+    }
+
+    class Observer implements BackPressedHandler {
+
+        private List<BackPressedHandler> mBackPressedHandlers = new ArrayList<>();
+
+        @Override
+        public boolean onBackPressed() {
+            for (BackPressedHandler handler : mBackPressedHandlers) {
+                if (handler.onBackPressed()) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        public void registerHandler(BackPressedHandler handler) {
+            mBackPressedHandlers.add(handler);
         }
     }
 }