一手遮天 Android

项目地址 https://github.com/webabcd/AndroidDemo
作者 webabcd

一手遮天 Android - view（集合类）: ViewPager 和 FragmentStatePagerAdapter

示例如下:

/view/collection/ViewPagerDemo4.java

/**
 * ViewPager - 页面切换控件
 *     setCurrentItem() - 指定 ViewPager 当前显示的页面的索引位置
 *     setAdapter() - 指定用于为 ViewPager 呈现数据的 PagerAdapter 对象
 *
 * 本例演示
 * 1、如何通过自定义的 FragmentStatePagerAdapter 来为 ViewPager 对象提供数据
 * 2、FragmentStatePagerAdapter 会缓存 3 个页，即当前页、左边页和右边页
 *    未被缓存的 fragment 会调用其 destroy
 * 3、FragmentPagerAdapter 会缓存 3 个页，即当前页、左边页和右边页
 *    未被缓存的 fragment 不会调用其 destroy
 */

package com.webabcd.androiddemo.view.collection;

import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentStatePagerAdapter;
import androidx.viewpager.widget.ViewPager;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.ViewGroup;

import com.webabcd.androiddemo.R;

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

public class ViewPagerDemo4 extends AppCompatActivity {

    private ViewPager mViewPager1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view_collection_viewpagerdemo4);

        mViewPager1 = findViewById(R.id.viewPager1);

        sample();
    }

    private void sample() {
        // 用于保存 ViewPager 的每个 fragment
        final ArrayList fragmentList = new ArrayList<Fragment>();
        fragmentList.add(ViewPagerDemo4_Fragment.newInstance(0xffff0000));
        fragmentList.add(ViewPagerDemo4_Fragment.newInstance(0xff00ff00));
        fragmentList.add(ViewPagerDemo4_Fragment.newInstance(0xff0000ff));
        fragmentList.add(ViewPagerDemo4_Fragment.newInstance(0xff000000));
        fragmentList.add(ViewPagerDemo4_Fragment.newInstance(0xffffffff));

        // 实例化自定义的 FragmentStatePagerAdapter
        MyFragmentPagerAdapter myFragmentPagerAdapter = new MyFragmentPagerAdapter(getSupportFragmentManager(), fragmentList);
        // 指定 ViewPager 的 FragmentStatePagerAdapter
        mViewPager1.setAdapter(myFragmentPagerAdapter);
    }

    /**
     * 自定义 FragmentStatePagerAdapter 用于为 ViewPager 提供数据
     */
    class MyFragmentPagerAdapter extends FragmentStatePagerAdapter {
        private List<Fragment> mFragmentList;
        private FragmentManager mFragmentManager;

        public MyFragmentPagerAdapter(FragmentManager fragmentManager, List<Fragment> fragmentList){
            super(fragmentManager);

            this.mFragmentManager = fragmentManager;
            this.mFragmentList = fragmentList;
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            return super.instantiateItem(container, position);
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            super.destroyItem(container, position, object);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }
    }
}

viewcollectionViewPagerDemo4_Fragment.java

/**
 * 引用示例参见 view/collection/ViewPagerDemo4.java
 */

package com.webabcd.androiddemo.view.collection;

import android.os.Bundle;
import androidx.fragment.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.webabcd.androiddemo.R;
import com.webabcd.androiddemo.utils.Helper;

public class ViewPagerDemo4_Fragment extends Fragment {

    private final String LOG_TAG = "VP_Fragment";

    private int mBackgroundColor;

    public static ViewPagerDemo4_Fragment newInstance(int backgroundColor) {
        ViewPagerDemo4_Fragment fragment = new ViewPagerDemo4_Fragment();
        Bundle args = new Bundle();
        args.putInt("backgroundColor", backgroundColor);
        fragment.setArguments(args);
        return fragment;
    }

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

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_view_collection_viewpagerdemo4, container, false);
        view.setBackgroundColor(mBackgroundColor);

        // 用于验证 FragmentStatePagerAdapter 会缓存 3 个页，即当前页、左边页和右边页；未被缓存的 fragment 会调用其 destroy
        Log.d(LOG_TAG + "_" + Helper.int2Hex(mBackgroundColor), "onCreateView");

        return view;
    }

    @Override
    public void onResume() {
        // 用于验证 FragmentStatePagerAdapter 会缓存 3 个页，即当前页、左边页和右边页；未被缓存的 fragment 会调用其 destroy
        Log.d(LOG_TAG + "_" + Helper.int2Hex(mBackgroundColor), "onResume");

        super.onResume();
    }

    @Override
    public void onPause() {
        // 用于验证 FragmentStatePagerAdapter 会缓存 3 个页，即当前页、左边页和右边页；未被缓存的 fragment 会调用其 destroy
        Log.d(LOG_TAG + "_" + Helper.int2Hex(mBackgroundColor), "onPause");

        super.onPause();
    }

    @Override
    public void onDestroy() {
        // 用于验证 FragmentStatePagerAdapter 会缓存 3 个页，即当前页、左边页和右边页；未被缓存的 fragment 会调用其 destroy
        Log.d(LOG_TAG + "_" + Helper.int2Hex(mBackgroundColor), "onDestroy");

        super.onDestroy();
    }
}

/layout/activity_view_collection_viewpagerdemo4.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPager1"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </androidx.viewpager.widget.ViewPager>

</LinearLayout>

/layout/fragment_view_collection_viewpagerdemo4.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

</FrameLayout>

项目地址 https://github.com/webabcd/AndroidDemo
作者 webabcd