flutter-go/lib/views/fourth_page.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_go/components/fourth_page_feature/page_dragger.dart';
import 'package:flutter_go/components/fourth_page_feature/page_reveal.dart';
import 'package:flutter_go/components/fourth_page_feature/pager_indicator.dart';
import 'package:flutter_go/components/fourth_page_feature/pages.dart';

import '../components/comp_list.dart';

class FourthPage extends StatefulWidget {
  @override
  FourthPageState createState() => new FourthPageState();
}

class FourthPageState extends State<FourthPage> with TickerProviderStateMixin {

  StreamController<SlideUpdate> slideUpdateStream;
  AnimatedPageDragger animatedPageDragger;

  int activeIndex = 0 ;
  SlideDirection slideDirection = SlideDirection.none;
  int nextPageIndex = 0 ;
  double slidePercent= 0.0;

  FourthPageState(){
    slideUpdateStream = new StreamController<SlideUpdate>();

    slideUpdateStream.stream.listen((SlideUpdate event){
      setState(() {
        if( event.updateType == UpdateType.dragging){
          slideDirection = event.direction;
          slidePercent = event.slidePercent;

          if( slideDirection == SlideDirection.leftToRight ){
            nextPageIndex = activeIndex - 1;
          } else if (slideDirection == SlideDirection.rightToLeft){
            nextPageIndex = activeIndex + 1;
          } else{
            nextPageIndex = activeIndex;
          }
        } else if( event.updateType == UpdateType.doneDragging){
          if(slidePercent > 0.5){

            animatedPageDragger = new AnimatedPageDragger(
              slideDirection: slideDirection,
              transitionGoal: TransitionGoal.open,
              slidePercent: slidePercent,
              slideUpdateStream: slideUpdateStream,
              vsync: this,
            );

          } else{
            animatedPageDragger = new AnimatedPageDragger(
              slideDirection: slideDirection,
              transitionGoal: TransitionGoal.close,
              slidePercent: slidePercent,
              slideUpdateStream: slideUpdateStream,
              vsync: this,
            );

            nextPageIndex = activeIndex;
          }

          animatedPageDragger.run();
        }
        else if( event.updateType == UpdateType.animating){
          slideDirection = event.direction;
          slidePercent = event.slidePercent;
        }

        else if (event.updateType == UpdateType.doneAnimating){
          activeIndex = nextPageIndex;

          slideDirection = SlideDirection.none;
          slidePercent = 0.0;

          animatedPageDragger.dispose();
        }
      });
    });


  }

  @override
  Widget build(BuildContext context) {
    return new Stack(
      children: [
        new Page( // page 的主要内容
          viewModel: pages[activeIndex],
          percentVisible: 1.0 ,
        ),
        new PageReveal(
          revealPercent: slidePercent,
          child: new Page(
            viewModel: pages[nextPageIndex],
            percentVisible: slidePercent ,
          ),
        ),
        new PagerIndicator(
          viewModel: new PagerIndicatorViewModel(
            pages,
            activeIndex,
            slideDirection,
            slidePercent,
          ),
        ),
        new PageDragger(
          canDragLeftToRight: activeIndex > 0 ,
          canDragRightToLeft: activeIndex < pages.length - 1 ,
          slideUpdateStream: this.slideUpdateStream,
        )
      ],
    );
  }
}