Xamarin.Android 利用作业计划程序实现ImageSwitcher图片自动定时轮播

在开发android程序时，遇到一个问题，ImageSwitcher只支持手动的切换图片，不支持自动定时的切换。因为xamarin的资料很少，官方也没有相应的教程，所以想到这个方法，利用job程序来实现后台的操作。

布局文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:minWidth="25px"
    android:minHeight="25px"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/relativeLayout1"
    android:background="#ffececec">
    <ImageView
        android:src="@drawable/ImgSlideLeft"
        android:layout_width="50px"
        android:layout_height="wrap_content"
        android:id="@+id/btnFeatureLeft"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true" />
    <ImageSwitcher
        android:minWidth="25px"
        android:minHeight="25px"
        android:layout_width="match_parent"
        android:layout_height="638px"
        android:id="@+id/SwitcherProductFeature"
        android:layout_centerInParent="true" />
    <ImageView
        android:src="@drawable/ImgSlideRight"
        android:layout_width="50px"
        android:layout_height="wrap_content"
        android:id="@+id/btnFeatureRight"
        android:layout_centerVertical="true"
        android:layout_alignParentRight="true" />
</RelativeLayout>

复制相应图片资源

后台代码：注意这里继承了GestureDetector.IOnGestureListener，监听用户的相关事件。代码中只写了 左滑和右滑事件。

[Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
    public class MainActivity : AppCompatActivity, ViewSwitcher.IViewFactory, GestureDetector.IOnGestureListener
    {
        private GestureDetector gestureDetector = null;
        private ImageSwitcher imageSwitcher;
        private int[] imgs = new int[]{
                    Resource.Drawable.p1,
                    Resource.Drawable.p2,
                    Resource.Drawable.p3,
                    Resource.Drawable.p4,
                    Resource.Drawable.p5,
                    Resource.Drawable.p6
                };
        private int currentPosition;
        public TestJobService testjobservice;
        public TextView t1;
        Handler handler;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            //关键是这里，将MainActivity传给TestJobService类
            handler = new Handler((Message msg) =>
            {
                testjobservice = (TestJobService)msg.Obj;
                testjobservice.setUiCallback(this);
            });

            SetContentView(Resource.Layout.activity_main);
            gestureDetector = new GestureDetector(this);
            imageSwitcher = FindViewById<ImageSwitcher>(Resource.Id.SwitcherProductFeature);
            currentPosition = 0;
            imageSwitcher.SetFactory(this);
            imageSwitcher.SetImageResource(Resource.Drawable.p1);

            t1 = FindViewById<TextView>(Resource.Id.tv1);

            Intent intent = new Intent(this, typeof(TestJobService));
            intent.PutExtra("messenger", new Messenger(handler));//传参
            StartService(intent);
            doService();
        }

        public View MakeView()
        {
            ImageView img = new ImageView(this);
            img.SetBackgroundColor(Android.Graphics.Color.Transparent);
            img.SetScaleType(ImageView.ScaleType.FitCenter);
            return img;
        }

        public override bool OnTouchEvent(MotionEvent e)
        {
            return gestureDetector.OnTouchEvent(e);
        }

        public bool OnFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY)
        {
            if (e2.GetX() - e1.GetX() > 100)
            {
                currentPosition--;
                if (currentPosition < 0)
                    currentPosition = imgs.Length - 1;
                //imageSwitcher.SetInAnimation(this, Android.Resource.Animation.FadeIn);//设置淡入动画
                //imageSwitcher.SetInAnimation(this, Android.Resource.Animation.FadeOut);
                imageSwitcher.SetImageResource(imgs[currentPosition]);
            }
            else if (e2.GetX() - e1.GetX() < -100)
            {
                currentPosition++;
                if (currentPosition > imgs.Length - 1)
                    currentPosition = 0;
                //imageSwitcher.SetInAnimation(this, Android.Resource.Animation.FadeIn);//设置淡入动画
                //imageSwitcher.SetInAnimation(this, Android.Resource.Animation.FadeOut);
                imageSwitcher.SetImageResource(imgs[currentPosition]);
            }
            return true;
        }

        public bool OnDown(MotionEvent e)
        {
            return false;
        }

        public void OnLongPress(MotionEvent e)
        {
        }

        public bool OnScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY)
        {
            return false;
        }

        public void OnShowPress(MotionEvent e)
        {
        }

        public bool OnSingleTapUp(MotionEvent e)
        {
            return false;
        }

        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
        {
            Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

            base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
        }

        private void doService()
        {
            JobScheduler jobScheduler = (JobScheduler)GetSystemService(JobSchedulerService);
            ComponentName componentName = new ComponentName(this, Java.Lang.Class.FromType(typeof(TestJobService)));
            JobInfo jobinfo = new JobInfo.Builder(1001, componentName)
                .SetPeriodic(5000)  //设置每5秒钟执行一次
                .Build();
            jobScheduler.Schedule(jobinfo);
        }
        //自动切换主要在这里实现。
        public void OnReceivedStartJob()
        {
            currentPosition++;
            if (currentPosition > imgs.Length - 1)
                currentPosition = 0;
            imageSwitcher.SetImageResource(imgs[currentPosition]);
        }
    }

新建job处理类

[Service(Exported = true, Permission = "android.permission.BIND_JOB_SERVICE")]
    public class TestJobService : JobService
    {
        public int i = 0;
        MainActivity owner;
        public override bool OnStartJob(JobParameters args)
        {
            doJob (args);
            return false;
        }

        public override bool OnStopJob(JobParameters args)
        {
            Log.Info("服务停止", "stop job service");

            return true;
        }

        private void doJob(JobParameters args)
        {
            if (args.JobId == 1001)
            {
                owner.OnReceivedStartJob();//返回到主线程中操作。
            }
            else if(args.JobId==1002)
            {
                //这里可以扩展第二个或第三个，根据jobiD判断
            }

        }

        public void setUiCallback(MainActivity activity)
        {
            owner = activity;
        }

        public override StartCommandResult OnStartCommand(Intent intent, Android.App.StartCommandFlags flags, int startId)
        {
            var callback = (Messenger)intent.GetParcelableExtra("messenger");
            var m = Message.Obtain();
            m.What = 2;//如果有多种消息，可以通过这个参数进行判断，进行不同的操作
            m.Obj = this;
            try
            {
                callback.Send(m);
            }
            catch (RemoteException e)
            {
                Log.Error("Tag", e, "Error passing service object back to activity.");
            }
            return StartCommandResult.NotSticky;
        }
    }

运行效果图

我还添加了左右两个按钮，也可以添加事件，点击切换。

官方关于Android 作业计划程序的介绍请参考以下链接。

https://learn.microsoft.com/zh-cn/xamarin/android/platform/android-job-scheduler