RecyclerView是Android一个更强大的控件,其不仅可以实现和ListView同样的效果,还有优化了ListView中的各种不足。其可以实现数据纵向滚动,也可以实现横向滚动(ListView做不到横向滚动)。接下来讲解RecyclerView的用法。
RecyclerView 基本用法
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
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。
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 {
private List 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 fruitList){
mFruitList = fruitList;
}
@Override
public 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-
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。 -
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。 -
getItemCount()返回RecyclerView的子项数目。
-
修改 MainActivity.java
public class MainActivity extends AppCompatActivity {
private List fruitList = new ArrayList<>();
@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);
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：
image
修改RecyclerView 显示效果
横向滚动
修改 fruit_item.xml
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:
image
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
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:
image
StaggeredGridLayoutManager
StaggeredGridLayoutManager(瀑布流布局)
修改fruit_item.xml
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 fruitList = new ArrayList<>();
@Override
protected 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 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:
image
GridLayoutManager和StaggeredGridLayout的区别
image
image
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。
RecyclerView 的点击事件
修改 FruitAdapter.java
public class FruitAdapter extends RecyclerView.Adapter {
private List 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 fruitList){
mFruitList = fruitList;
}
@Override
public 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() {
@Override
public 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() {
@Override
public 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：
image