Android 2-10 RecyclerView
RecyclerView
本文章转载自https://www.jianshu.com/p/b4bb52cdbeb7
文章目录
- RecyclerView
- 添加RecyclerView 依赖库
- 修改 activity_main.xml
- 新建 Fruit.java
- 新建 fruit_item.xml
- 新增适配器 FruitAdapter
- 修改MainActivity.java
- 修改RecyclerView 显示效果
- 修改 fruit_item.xml
- 修改MainActivity.java
- GridLayoutManager
- 修改MainActivity.java
- StaggeredGridLayoutManager
- 修改fruit_item.xml
- 修改MainActivity.java
- GridLayoutManager和StaggeredGridLayout的区别
- Recycler的点击事件
因为RecyclerView属于新增的控件,Android将RecyclerView定义在support库里。若要使用RecyclerView,第一步是要在build.gradle中添加对应的依赖库。
添加RecyclerView 依赖库
在app/build.gradle中的dependencies闭包添加以下内容:
implementation 'com.android.support:recyclerview-v7:27.1.1'
然后点击顶部的Sync Now进行同步
修改 activity_main.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
><android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
</LinearLayout>
由于RecyclerView不是内置在系统SDK中,需要把其完整的包名路径写出来
新建 Fruit.java
public class Fruit {private String name;private int imageId;public Fruit(String name, int imageId) {this.name = name;this.imageId = imageId;}public String getName() {return name;}public int getImageId() {return imageId;}
}
新建 fruit_item.xml
创建ImageView来显示水果图片,TextView来显示水果名字。
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/fruit_image"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/fruitname"
android:layout_gravity="center_vertical"
android:layout_marginLeft="10dp"/>
</LinearLayout>
新增适配器 FruitAdapter
为RecyclerView新增适配器FruitAdapter,并让其继承于RecyclerView.Adapter,把泛型指定为FruitAdapter.ViewHolder。
public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {private List<Fruit> mFruitList;
static class ViewHolder extends RecyclerView.ViewHolder{ImageView fruitImage;
TextView fruitName;public ViewHolder (View view)
{super(view);
fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
fruitName = (TextView) view.findViewById(R.id.fruitname);
}}public FruitAdapter (List <Fruit> fruitList){mFruitList = fruitList;
}@Overridepublic ViewHolder onCreateViewHolder(ViewGroup parent, int viewType){View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
ViewHolder holder = new ViewHolder(view);
return holder;
}@Override
public void onBindViewHolder(ViewHolder holder, int position){Fruit fruit = mFruitList.get(position);
holder.fruitImage.setImageResource(fruit.getImageId());
holder.fruitName.setText(fruit.getName());
}@Override
public int getItemCount(){return mFruitList.size();
}
定义内部类ViewHolder,并继承RecyclerView.ViewHolder。传入的View参数通常是RecyclerView子项的最外层布局。
FruitAdapter构造函数,用于把要展示的数据源传入,并赋予值给全局变量mFruitList。
FruitAdapter继承RecyclerView.Adapter。因为必须重写onCreateViewHolder(),onBindViewHolder() 和getItemCount()三个方法
(1)onCreateViewHolder()用于创建ViewHolder实例,并把加载的布局传入到构造函数去,再把ViewHolder实例返回。
(2)onBindViewHolder()则是用于对子项的数据进行赋值,会在每个子项被滚动到屏幕内时执行。position得到当前项的Fruit实例。
(3)getItemCount()返回RecyclerView的子项数目。
修改MainActivity.java
public class MainActivity extends AppCompatActivity {private List<Fruit> fruitList = new ArrayList<>();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initFruits();RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);LinearLayoutManager layoutManager = new LinearLayoutManager(this);recyclerView.setLayoutManager(layoutManager);FruitAdapter adapter = new FruitAdapter(fruitList);recyclerView.setAdapter(adapter);}private void initFruits() {for (int i = 0; i < 2; i++) {Fruit apple = new Fruit("Apple", R.drawable.apple_pic);fruitList.add(apple);Fruit banana = new Fruit("Banana", R.drawable.banana_pic);fruitList.add(banana);Fruit orange = new Fruit("Orange", R.drawable.orange_pic);fruitList.add(orange);Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);fruitList.add(watermelon);Fruit pear = new Fruit("Pear", R.drawable.pear_pic);fruitList.add(pear);Fruit grape = new Fruit("Grape", R.drawable.grape_pic);fruitList.add(grape);Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);fruitList.add(pineapple);Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);fruitList.add(strawberry);Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);fruitList.add(cherry);Fruit mango = new Fruit("Mango", R.drawable.mango_pic);fruitList.add(mango);}}
}
LayoutManager用于指定RecyclerView的布局方式。LinearLayoutManager指的是线性布局。
运行效果:
修改RecyclerView 显示效果
修改 fruit_item.xml
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:orientation="vertical">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/fruit_image"
android:layout_gravity="center_horizontal"/><TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/fruitname"
android:layout_gravity="center_horizontal"
android:layout_marginTop="10dp"/>
</LinearLayout>
把LinearLayout改成垂直排列,因为水果名字长度不一样,把宽度改为100dp。
ImageView和TextView都改为水平居中
修改MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initFruits();RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);LinearLayoutManager layoutManager = new LinearLayoutManager(this);layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);recyclerView.setLayoutManager(layoutManager);FruitAdapter adapter = new FruitAdapter(fruitList);recyclerView.setAdapter(adapter);
}
通过调用setOrientation()把布局的排列方向改为水平排列。
得益于RecyclerView的设计,我们可以通过LayoutManager实现各种不同的排列方式的布局。
运行结果:
除了LinearLayoutManager,RecyclerView还提供了GridLayoutManager(网格布局)和StaggeredGridLayoutManager(瀑布流布局)
GridLayoutManager
GridLayoutManager(网格布局)
修改MainActivity.java
把
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
换成
GridLayoutManager layoutManager = new GridLayoutManager(this,5);
GridLayoutManager (Context context, int spanCount)
- Context: Current context, will be used to access resources.
- spanCount int: The number of columns in the grid(网格的列数)
运行结果:
StaggeredGridLayoutManager
StaggeredGridLayoutManager(瀑布流布局)
修改fruit_item.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="wrap_content"
android:layout_margin="5dp"
>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/fruit_image"
android:layout_gravity="center_horizontal"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/fruitname"
android:layout_gravity="left"
android:layout_marginTop="10dp"/>
</LinearLayout>
把LinearLayout的宽度设为match_parent是因为瀑布流的宽度是 根据布局的列数来自动适配的,而不是固定值 。(GridLayoutManager也是 根据布局的列数来自动适配的)。
修改MainActivity.java
public class MainActivity extends AppCompatActivity {private List<Fruit> fruitList = new ArrayList<>();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);initFruits();RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);recyclerView.setLayoutManager(layoutManager);FruitAdapter adapter = new FruitAdapter(fruitList);recyclerView.setAdapter(adapter);}private void initFruits() {for (int i = 0; i < 2; i++) {Fruit apple = new Fruit(getRandomLengthName("Apple"), R.drawable.apple_pic);fruitList.add(apple);Fruit banana = new Fruit(getRandomLengthName("Banana"), R.drawable.banana_pic);fruitList.add(banana);Fruit orange = new Fruit(getRandomLengthName("Orange"), R.drawable.orange_pic);fruitList.add(orange);Fruit watermelon = new Fruit(getRandomLengthName("Watermelon"), R.drawable.watermelon_pic);fruitList.add(watermelon);Fruit pear = new Fruit(getRandomLengthName("Pear"), R.drawable.pear_pic);fruitList.add(pear);Fruit grape = new Fruit(getRandomLengthName("Grape"), R.drawable.grape_pic);fruitList.add(grape);Fruit pineapple = new Fruit(getRandomLengthName("Pineapple"), R.drawable.pineapple_pic);fruitList.add(pineapple);Fruit strawberry = new Fruit(getRandomLengthName("Strawberry"), R.drawable.strawberry_pic);fruitList.add(strawberry);Fruit cherry = new Fruit(getRandomLengthName("Cherry"), R.drawable.cherry_pic);fruitList.add(cherry);Fruit mango = new Fruit(getRandomLengthName("Mango"), R.drawable.mango_pic);fruitList.add(mango);}}private String getRandomLengthName(String name) {Random random = new Random();int length= random.nextInt(20)+1; // 产生1-20的随机数StringBuilder builder = new StringBuilder();for (int i =0; i<length; i++) {builder.append(name);}return builder.function function toString() {[native code]}() {[native code]}();}
}
StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);StaggeredGridLayoutManager传入2个参数,第一个是布局的列数,第二个是布局的排列方向。
random.nextInt(20)+1 产生1-20的随机数
运行效果:
GridLayoutManager和StaggeredGridLayout的区别
GridLayoutManager
StaggerGridLayoutManager
上图是GridLayoutManager,下图是StaggeredGridLayout。
当从显示效果来看,已经一目了然。
GridLayoutManager是会固定高度的,所以会留下很多空白区域。
相反,StaggeredGridLayout并不会固定高度,以至于就算子项的高度不一致,下一行的会自动靠拢上一行。
Recycler的点击事件
修改FruitAdapter.java
public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {private List<Fruit> mFruitList;static class ViewHolder extends RecyclerView.ViewHolder {View fruitView;ImageView fruitImage;TextView fruitName;public ViewHolder (View view) {super(view);fruitView = view;fruitImage = (ImageView) view.findViewById(R.id.fruit_image);fruitName = (TextView) view.findViewById(R.id.fruitname);}}public FruitAdapter (List <Fruit> fruitList) {mFruitList = fruitList;}@Overridepublic ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);final ViewHolder holder = new ViewHolder(view);holder.fruitView.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View view) {int position = holder.getAdapterPosition();Fruit fruit = mFruitList.get(position);Toast.makeText(view.getContext(), "you clicked view" + fruit.getName(), Toast.LENGTH_SHORT).show();}});holder.fruitImage.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View view) {int position = holder.getAdapterPosition();Fruit fruit = mFruitList.get(position);Toast.makeText(view.getContext(), "you clicked image" + fruit.getName(), Toast.LENGTH_SHORT).show();}});return holder;}...
}
修改ViewHolder,添加fruitView变量来保存子项最外层布局的实例。
运行效果:
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