解决Flutter boost模块化加入到原有android项目后，首次加载过慢的问题

由于Flutter boost目前还没有很好的解决方案，所以只能魔改了，大致的思路就是在刚打开app的时候就初始化一个不可见的Flutter页面，让其自动注册&初始化。

先编写一个FlutterFragment

package xxx;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.taobao.idlefish.flutterboost.containers.BoostFlutterFragment;

import io.flutter.plugins.GeneratedPluginRegistrant;import java.util.HashMap;
import java.util.Map;

import io.flutter.plugin.common.PluginRegistry;

public class MagicFragment extends BoostFlutterFragment {
    public MagicFragment() {

    }

    public static MagicFragment instance(String tag) {
        MagicFragment fragment = new MagicFragment();
        fragment.setTabTag(tag);
        return fragment;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return super.onCreateView(inflater, container, savedInstanceState);
    }

    @Override
    public void setArguments(@Nullable Bundle args) {
        if (args == null) {
            args = new Bundle();
            args.putString("tag", "");
        }
        super.setArguments(args);
    }

    public void setTabTag(String tag) {
        Bundle args = new Bundle();
        args.putString("tag", tag);
        super.setArguments(args);
    }

    @Override
    public void onRegisterPlugins(PluginRegistry registry) {
        GeneratedPluginRegistrant.registerWith(registry);
    }

    @Override
    public String getContainerName() {
        return "";
    }

    @Override
    public Map getContainerParams() {
        Map<String, String> params = new HashMap<>();
        return params;
    }

    @Override
    public void destroyContainer() {

    }

    @Override
    public void onContainerShown() {
        super.onContainerShown();
    }

}

然后在应用的第一个页面的Activity中加入一个不可见的FrameLayout

<FrameLayout
            android:id="@+id/magic"
            android:layout_width="1dp"
            android:layout_height="1dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"></FrameLayout>

然后在应用的第一个页面的Activity中加入一个方法，把这个Fragment加入到这个Activity中

private fun addMagicFragment() {
        var time: Long = System.currentTimeMillis()
        val instance = instance("magic")
        val fm = supportFragmentManager
        val ft = fm.beginTransaction()
        val cacheFragment = fm.findFragmentByTag("magic")
        if (cacheFragment != null) {
            ft.show(cacheFragment)
        } else {
            ft.add(R.id.magic, instance)
        }
        ft.commit()
    }

这样每次打开app就会第一时间去初始化Flutter了。