ViewPager - Android

本篇文章记录的是Android应用中的ViewPager的使用.

PageAdapter

PageAdapter 用于向ViewPager中提供视图.

getCount

获得ViewPager中有多少个view.

instantiateItem

1.将给定位置的view添加到ViewGroup容器中,创建并显示出来

2.返回一个代表新增页面的Object(key),直接返回view本身就行,也可以自动以,但是key和每个view要一一对应.

isViewFromObject

判断instantiateItem(ViewGroup,int)函数所返回来的key与一个页面视图是否是代表的同一个视图,通常直接写 view==object

destoryItem

移除一个给定位置的页面.适配器有责任从容器中删除这个视图.这是为了确保在finishUpdate(viewGroup)返回时视图能够被移除.

代码示例

布局XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/pink"
    android:orientation="horizontal">

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

另外两个布局XML,随便定义

PageViewerAdapter.java



package com.example.myapplication.adapter;

import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.viewpager.widget.PagerAdapter;

import java.util.ArrayList;

public class PageViewerAdapter extends PagerAdapter {

    private final ArrayList<View> list;

    public PageViewerAdapter(ArrayList<View> data) {
        list = data;
    }
    @Override
    public int getCount() {
        return list.size();
    }
    
 
    // object 是instantiateItem返回的key.
    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return view == object;
    }


    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        View v = list.get(position);
        container.addView(v);
        // 返回的是一个key用于在isViewFromObject中比较元素是否相同
        return v;
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        super.destroyItem(container, position, object);
        View v = list.get(position);
        container.removeView(v);
    }
}

MainActivity.java.

package com.example.myapplication;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager.widget.ViewPager;
import com.example.myapplication.adapter.PageViewerAdapter;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
    private final String TAG = "ysd";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ArrayList<View> list = new ArrayList<View>();
        ViewPager pager = findViewById(R.id.vp);
        LayoutInflater inflate = LayoutInflater.from(this);
        list.add(inflate.inflate(R.layout.notify, null));
        list.add(inflate.inflate(R.layout.popup_window, null));
        pager.setAdapter(new PageViewerAdapter(list));
    }
    @Override
    protected void onRestart() {
        super.onRestart();
    }
    @Override
    protected void onPostResume() {
        super.onPostResume();
    }
}

上面代码执行完毕之后,会得到诸如下面的动态图:

VeryCapture_20230901064853.gif