为什么 viewPager 会导致内存泄漏？

Question

在我的应用程序中，我在 viewPager 中使用，它使用 FragmentStatePagerAdapter 调整片段。每个片段包含 gridView 和 GridViewAdapter。

一切正常，但每次交换时，内存使用量都会增加很多并浪费内存。为什么会发生，我该如何解决？

片段适配器class:

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;

import java.util.Calendar;


public class FragmentAdapter extends FragmentStatePagerAdapter {

    private static final int NUM_ITEMS = 12;


    public FragmentAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case Calendar.JANUARY:
                return MonthFragment.newInstance(Calendar.JANUARY);
            case Calendar.FEBRUARY:
                return  MonthFragment.newInstance(Calendar.FEBRUARY);
            case Calendar.MARCH:
                return MonthFragment.newInstance(Calendar.MARCH);
            case Calendar.APRIL:
                return  MonthFragment.newInstance(Calendar.APRIL);
            case Calendar.MAY:
                return  MonthFragment.newInstance(Calendar.MAY);
            case Calendar.JUNE:
                return  MonthFragment.newInstance(Calendar.JUNE);
            case Calendar.JULY:
                return  MonthFragment.newInstance(Calendar.JULY);
            case Calendar.AUGUST:
                return  MonthFragment.newInstance(Calendar.AUGUST);
            case Calendar.SEPTEMBER:
                return  MonthFragment.newInstance(Calendar.SEPTEMBER);
            case Calendar.OCTOBER:
                return  MonthFragment.newInstance(Calendar.OCTOBER);
            case Calendar.NOVEMBER:
                return MonthFragment.newInstance(Calendar.NOVEMBER);
            case Calendar.DECEMBER:
                return MonthFragment.newInstance(Calendar.DECEMBER);
            default:
                throw new IllegalArgumentException("there is problem with position", new Throwable("NUM_ITEMS is not 12"));
        }
    }

    @Override
    public int getCount() {
        return NUM_ITEMS;
    }

}

MonthFragment class:

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.GridView;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;


public class MonthFragment extends Fragment {

    private static final String ARG_MONTH = "arg_month";
    private int fragmentMonthId;

    private GridView gridView;
    private GridViewAdapter adapter;
    private ArrayList<Date> monthDates;

    public MonthFragment() {
        // Required empty public constructor
    }


    public static MonthFragment newInstance(int monthId) {
        MonthFragment fragment = new MonthFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_MONTH, monthId);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            fragmentMonthId = getArguments().getInt(ARG_MONTH);
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_month, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        gridView = view.findViewById(R.id.days);

        monthDates = getDates();
        adapter = new GridViewAdapter(getContext(), R.layout.day, 0, monthDates);

        gridView.setAdapter(adapter);
    }

    private ArrayList<Date> getDates() {
        ArrayList<Date> arrayList = new ArrayList<>();
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_MONTH, 1);
        calendar.set(Calendar.MONTH, fragmentMonthId);
        calendar.set(Calendar.YEAR, calendar.get(Calendar.YEAR));
        for (int i = 0; i < calendar.getMaximum(Calendar.DAY_OF_MONTH); i++) {
            arrayList.add(calendar.getTime());
            calendar.add(Calendar.DATE, 1);
        }
        return arrayList;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        monthDates.clear();
        adapter = null;
        gridView.setAdapter(null);
        gridView = null;
    }
}

GridViewAdapter class:

package com.example.kobimoshe.calendarwithpager;

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;


public class GridViewAdapter extends ArrayAdapter<Date> {

    ArrayList<Date> datesList;

    public GridViewAdapter(@NonNull Context context, int resource, int textViewResourceId, @NonNull List<Date> objects) {
        super(context, resource, textViewResourceId, objects);
        datesList = (ArrayList<Date>) objects;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(getContext()).inflate(R.layout.day, parent, false);
        }
        TextView dateView = (TextView) convertView.findViewById(R.id.date);
        dateView.setText(datesList.get(position).toString());

        return convertView;
    }

}

更新：

经过实验和研究，我假设两件事：

GC 不会删除片段内的元素，即使我在片段被销毁时删除了它们（我假设是因为当 onDestroyView 被调用时内存使用图没有减少） .
每次交换也会造成内存泄漏（我用 ViewPager 创建了一个新的，它使用 FragmentStatePagerAdapter 来设置空片段。每次在此应用程序中交换片段时，内存使用量都会增加）。

谁能给我解释一下为什么不能完全删除元素？如何修复代码以便在删除片段时清理它们？即使片段以某种方式从中删除，保存在内存中。如何从内存中删除片段以节省恒定的内存大小？

Answer 1

检查你的引用，99% 的时间内存泄漏是由应该被垃圾收集但仍然存在的持久对象引起的。确保摆脱不再使用的对象。

此外，当您有大量片段并且在页面之间切换时会增加一些开销时，FragmentStatePagerAdapter 效果最佳。考虑尝试 FragmentPagerAdapter，它更适合少量片段。正如已经提到的，你应该实施 viewholder pattern 因为你有一个视图列表。

Answer 2

我已成功解决问题

在片段 class 的 onDetach 方法中，我删除了所有子片段引用。然后，我调用 Runtime.getRuntime().gc() 以强制 GC 从未使用的元素中清理内存；

为什么 viewPager 会导致内存泄漏？

why viewPager cause memory leak?

android

memory-leaks

android-fragments

android-viewpager

android-pageradapter