切换BottomNavigationView中的标签时滞后 [英] Lag when switching tabs in BottomNavigationView

问题描述

我有一个包含BottomNavigationView的Activity，此bottomnav帮助该活动显示三个片段.这些片段加载得很好，并且我使用AsyncTask来执行所有繁重的操作，而在UI线程中，我将显示一个ProgressBar，直到一切加载完毕.
我的片段有一个怪异的行为:第一次加载片段时，要花一些时间才能真正显示它，而不是用进度条立即显示它.
这件事只会在第一次发生，并且只会在这个片段中发生.
片段代码仅包含以下内容:

I have an Activity that contains a BottomNavigationView, and this bottomnav helps the activity to display three fragments. These fragments load well, and I use an AsyncTask to do every heavy operation, while in the UI thread, I show a ProgressBar until everything loads.
There is a weird behaviour with my fragment: The first time I load the fragment it takes some time to actually display it, instead of displaying it instantly with a progressbar.
This thing only happens the first time, and only in this fragment.
The fragment code only contains this:

@Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        new LoadData(getView(), getContext()).execute();
    }

private class LoadData extends AsyncTask<Void, Void, Void> {

        private View v;
        private Context context;

        public LoadData(View v, Context context) {
            items = new ArrayList<>();
            this.v = v;
            this.context = context;
        }

        @Override
        protected Void doInBackground(Void... voids) {
            setItems(context); //Heavy operation
            adapter = new DashAdapter(items, context);
            return null;
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            //shows progressbar
            progress = v.findViewById(R.id.DFProgress);
            progress.setVisibility(View.VISIBLE);
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            setPager();
            //sets viewPager and hides progressbar
            progress.setVisibility(View.GONE);
        }
    }

在下面的gif中，如果查看底部的bottomnavigation视图，则可以看到显示该片段需要花费时间.但是，在尝试第二次加载片段之后，它会按预期加载.

In the gif below, if you look at the bottomnavigationview at the bottom, you can see that it takes time to display the fragment. But after trying to load the fragment a second time, it loads as expected.

如何制作片段以正确的方式加载?

How could I make the fragment to load the right way?

推荐答案

我遇到了同样的问题.我有两个选择.

I had the same problem. I have two options.

1. 在调用LoadData时使用postdelay或
2. 首先手动添加所有片段.您可以自己管理navigationItemSelected.

喜欢这个:

val firstFragment: Fragment = FirstFragment()
val secondFragment: Fragment = SecondFragment()
val thirdFragment: Fragment = ThirdFragment()

val navView: BottomNavigationView = findViewById(R.id.nav_view)

var active = firstFragment
fm.beginTransaction().add(R.id.nav_host_fragment, thirdFragment, "3").hide(thirdFragment).commit()
fm.beginTransaction().add(R.id.nav_host_fragment, secondFragment, "2").hide(secondFragment).commit()
fm.beginTransaction().add(R.id.nav_host_fragment, firstFragment, "1").commit()

navView.setOnNavigationItemReselectedListener {  }
navView.setOnNavigationItemSelectedListener { item ->
       when (item.itemId) {
           R.id.navigation_first -> {
               fm.beginTransaction().hide(active).show(firstFragment).commit()
               active = firstFragment

           }
           R.id.navigation_second -> {
               fm.beginTransaction().hide(active).show(secondFragment).commit()
               active = secondFragment
           }
           R.id.navigation_third -> {
               fm.beginTransaction().hide(active).show(thirdFragment).commit()
               active = thirdFragment
           }
       }
        true
   }

并在nav_host_fragment中删除这些行:

And remove these lines in your nav_host_fragment:

app:defaultNavHost="true"
app:navGraph="@navigation/mobile_navigation"

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