feat(frame-service): extend FrameService to provide reusable frames

FrameServices should be responsible for delivering the correct topmost frame too

Author: ADjenkov

Diff for: nativescript-angular/platform-providers.ts

@@ -66,7 +66,69 @@ export const defaultPageFactoryProvider = { provide: PAGE_FACTORY, useValue: def
 @Injectable()
 export class FrameService {
     // TODO: Add any methods that are needed to handle frame/page navigation
+    private frames: { frame: Frame, name: string, rootOutlet: string }[] = [];
+
+    // Return the topmost frame.
+    // TabView with frames scenario: topmost() will return the root TabViewItem frame,
+    // which could be the wrong topmost frame (modal with nested frame e.g.):
+    // TabViewItem -> Frame -> Modal -> Frame2 -> Frame2-Navigation
     getFrame(): Frame {
-        return topmost();
+        let tompostFrame = topmost();
+        const { cachedFrame, cachedFrameRootOutlet } = this.findFrame(tompostFrame);
+
+        if (cachedFrame && cachedFrameRootOutlet) {
+            const latestFrameByOutlet = this.getLatestFrameByOutlet(cachedFrameRootOutlet);
+
+            if (latestFrameByOutlet && latestFrameByOutlet !== cachedFrame) {
+                tompostFrame = latestFrameByOutlet;
+            }
+        }
+
+        return tompostFrame;
+    }
+
+    addFrame(frame: Frame, name: string, rootOutlet: string) {
+        this.frames.push({ frame: frame, name: name, rootOutlet: rootOutlet });
+    }
+
+    removeFrame(frame: Frame) {
+        this.frames = this.frames.filter(currentFrame => currentFrame.frame !== frame);
+    }
+
+    findFrame(frame: Frame, name?: string) {
+        let cachedFrame;
+        let cachedFrameRootOutlet;
+        let hasDuplicateOutlet = false;
+
+        for (let i = 0; i < this.frames.length; i++) {
+            const currentFrame = this.frames[i];
+
+            if (currentFrame.frame === frame) {
+                cachedFrame = currentFrame;
+                cachedFrameRootOutlet = currentFrame.rootOutlet;
+            }
+
+            if (name && currentFrame.name === name) {
+                hasDuplicateOutlet = true;
+            }
+        }
+
+        return { cachedFrame, cachedFrameRootOutlet, hasDuplicateOutlet };
+    }
+
+    // Return the latest navigated frame from the given outlet branch.
+    private getLatestFrameByOutlet(rootOutlet: string): Frame {
+        let frame: Frame;
+
+        for (let i = this.frames.length - 1; i > 0; i--) {
+            const currentFrame = this.frames[i];
+
+            if (currentFrame.rootOutlet === rootOutlet) {
+                frame = currentFrame.frame;
+                break;
+            }
+        }
+
+        return frame;
     }
 }