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: