当片段寻呼机适配器的片段出现在屏幕上时，将调用哪个生命周期回调? [英] Which lifecycle callback is called when a fragment pager adapter's fragment comes to screen?

问题描述

我想检测我使用 ViewPager 设置的三个片段中的特定片段何时出现在屏幕上.我在 viewpager 中有 3 个片段，并使用

I want to detect when a particular fragment of three fragments I have set up with a ViewPager comes on to screen. I have 3 fragments in the viewpager and have set up the viewpager with

mViewPager.setOffscreenPageLimit(2);

所以所有三个片段都是一次构建的(因为它在每一侧存储 2 个).我检查了 Fragment.onResume() 只被调用一次，而不是在每个片段出现时调用.是否有另一个回调来确保我可以捕获此事件并为其发送一些分析信号?

so all three fragments are constructed at once (since it stores 2 on each side). I checked that Fragment.onResume() is called just once and not when each fragment comes to the foreground. Is there another callback to ensure I can catch this event and send some analytics signal for it?

谢谢

推荐答案

您可以使用 ViewPager.setOnPageChangeListener() 设置一个 ViewPager.OnPageChangeListener().

You can use the ViewPager.setOnPageChangeListener() to set a ViewPager.OnPageChangeListener().

根据所选页面在 PagerAdapter 中的位置使用其侦听器.

Use the listener for the selected page based on its position in the PagerAdapter.

这是我的示例应用:

package net.ynotapps.testviewpagerfragment;

import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

import butterknife.ButterKnife;
import butterknife.InjectView;


public class MainActivity extends ActionBarActivity {


    @InjectView(R.id.pager)
    ViewPager pager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ButterKnife.inject(this);

        CustomPagerAdapter adapter = new CustomPagerAdapter(getSupportFragmentManager());
        pager.setAdapter(adapter);
        pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {

                // Put Code here //

                // Example code //
                if (position == 2) {
                    Toast.makeText(MainActivity.this, "Found Position 2 fragment", Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }


    public static class CustomPagerAdapter extends FragmentPagerAdapter {

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

        @Override
        public Fragment getItem(int position) {
            CustomFragment fragment = new CustomFragment();
            Bundle bundle = new Bundle();
            bundle.putString("display_text", String.format("Fragment %d is here.", position));
            fragment.setArguments(bundle);
            return fragment;
        }

        @Override
        public int getCount() {
            return 5;
        }
    }

    public static class CustomFragment extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
            TextView tv = new TextView(getActivity());
            tv.setText(getArguments().getString("display_text"));
            return tv;
        }
    }
}

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