ListView絕對可以稱得上是Android中最常用的控件之一。
ListView的簡單用法：
首先listview是用來展示大量數(shù)據(jù)。那我們就應該先將數(shù)據(jù)提供好。當然數(shù)組中的數(shù)據(jù)是無法直接傳給ListView的，這時候我們就需要適配器。例:ArrayAdapter。
在ArrayAdapter的構(gòu)造函數(shù)中依次傳入當前上下文、ListView子項布局的id，
以及要適配的數(shù)據(jù)。最后調(diào)用ListView的setAdapter()方法將構(gòu)建好的適配器對象傳遞進去，就這樣ListView和數(shù)據(jù)之間的關(guān)系就建立完成了。
定制ListView的界面
在大多數(shù)情況下，系統(tǒng)的ListView無法滿足業(yè)務(wù)需求，這時候我們就需要對ListView的界面進行定制。
舉個例子：
- 定義一個實體類，作為ListView適配器的適配類型
public class Fruit {
private String name;
private int imageId;
...
}
- 為ListVIew的子項指定一個我們自定義的布局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="@+id/fruit_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/fruit_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:layout_marginLeft="10dp"/>
</LinearLayout>
- 創(chuàng)建一個自定義的適配器，此適配器繼承ArrayAdapter，并將泛型指向?qū)嶓w類：
public class FruitAdapter extends ArrayAdapter<Fruit> {
private int resourceId;
LayoutInflater mInflater = null;
public FruitAdapter(Context context , int textViewResourceId , List<Fruit> objects) {
super(context,textViewResourceId,objects);
resourceId = textViewResourceId;
}
@NonNull
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position);//獲取當前項的Fruit實例
//將加載好的布局進行緩存，可重用
View view;
ViewHolder viewHolder;
if (convertView == null){
view = mInflater.inflate(resourceId,parent,false);
viewHolder = new ViewHolder();
viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
view.setTag(viewHolder);
}else {
view = convertView;
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());
return view;
}
//借助ViewHolder，將控件進行緩存，可重用
class ViewHolder{
ImageView fruitImage;
TextView fruitName;
}
}
- MainActivity繼承BaseActivity
//BaseActivity
public abstract class BaseActivity extends AppCompatActivity{
protected Context mContext;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.mContext = this;
int layoutId = getLayoutId();
View contentView = LayoutInflater.from(mContext).inflate(layoutId,null,false);
setContentView(contentView);
hideActionBar();
initData();
initView();
initList();
}
/**
*初始化數(shù)據(jù)
*/
public abstract void initData();
/**
*初始化界面
*/
public abstract void initView();
/**
*隱藏標題欄
*/
public void hideActionBar(){
ActionBar actionBar = getSupportActionBar();
if (actionBar != null){
actionBar.hide();
}
}
/**
* 獲取布局文件的id
*
* @return
*/
public abstract int getLayoutId();
}
//MainActivity
public class MainActivity extends BaseActivity implements AdapterView.OnItemClickListener{
private List<Fruit> fruitList = new ArrayList<>();
@Override
public void initData() {
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);
}
}
@Override
public void initView() {
FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
ListView listView = (ListView) findViewById(R.id.list_view);
listView.setAdapter(adapter);
listView.setOnItemClickListener(this);
}
@Override
public int getLayoutId() {
return R.layout.activity_main;
}
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//點擊listView子項，彈出提示框顯示該子項的Name
Fruit fruit = fruitList.get(position);
Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_SHORT).show();
}
}
好至此就完成這個小例子了。
更強大的滾動控件——RecyclerView：
可以說RecyclerView是優(yōu)化和強化過的ListView，Android官方也推薦使用RecyclerView。
舉個例子：
- RecyclerView也屬于新增的控件，所以要先導包。
在app/build.gradle中：
compile 'com.android.support:recyclerview-v7:24.2.1' - 仿上一個ListView例子：
同樣準備一個Fruit類和fruit_item.xml，新建一個FruitAdapter類，讓這個類繼承自RecyclerView.Adatper，并將泛型指定為FruitAdapter.ViewHolder。
public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder>{
private List<Fruit> mFruitList;
/**
*定義一個ViewHolder的類，在ViewHolder的構(gòu)造函數(shù)中傳入一個View參數(shù)，
*這個參數(shù)通常為RecyclerView子項的最外層布局。
*/
static class ViewHolder extends RecyclerView.ViewHolder{
ImageView fruitImage;
TextView fruitName;
public ViewHolder(View itemView) {
super(itemView);
fruitImage = (ImageView) itemView.findViewById(R.id.fruit_image);
fruitName = (TextView) itemView.findViewById(R.id.fruit_name);
}
}
//構(gòu)造函數(shù)，用于取數(shù)據(jù)源
public FruitAdapter(List<Fruit> mFruitList) {
this.mFruitList = mFruitList;
}
//用于創(chuàng)建ViewHolder實例。在此，我們將子項布局加載進來，然后傳入構(gòu)造函數(shù)，最后返回viewHolder。
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
ViewHolder viewHolder = new ViewHolder(view);
return viewHolder;
}
//用于對RecyclerView子項的數(shù)據(jù)進行賦值，會在每個子項被滾動到屏幕內(nèi)執(zhí)行。
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
Fruit fruit = mFruitList.get(position);
holder.fruitImage.setImageResource(fruit.getImageId());
holder.fruitName.setText(fruit.getName());
}
//子項的個數(shù)
@Override
public int getItemCount() {
return mFruitList.size();
}
}
- MainActivity
@Overridepublic void initView() {
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
FruitAdapter adapter = new FruitAdapter(fruitList);
recyclerView.setAdapter(adapter);
}
初始化界面中，我們先獲取到RecyclerView的實例，然后通過LinearLayoutManager對象以setLayoutManager()方法設(shè)置RecyclerView的布局方式（這里使用的LinearLayoutManager是線性布局的意思）
然后實例一個adapter，通過setAdapter()完成適配器設(shè)置。
實現(xiàn)橫向滾動和瀑布流布局
其實實現(xiàn)橫向滾動很簡單，就如上面的例子。我們只要設(shè)置layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL)就行了。
RecyclerView能輕松實現(xiàn)這些效果的原因是RecyclerView的布局排列是交給LayoutManager管理的，而LayoutManager中制定了一套可擴展的布局排列接口，子類只要按接口規(guī)范來實現(xiàn)，就能制定出各種不同的排列方式的布局了。
同樣RecyclerView還提供了GridLayoutManager和StaggeredGridLayoutManager這兩種內(nèi)置的布局排列方式。
GridLayoutManager：實現(xiàn)網(wǎng)格布局
StaggeredGridLayoutManager：實現(xiàn)瀑布流布局
實現(xiàn)瀑布流布局只要加這句就可以了StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);
參數(shù)一：指定布局的列數(shù)；參數(shù)二：指定布局的排列方向，這里是縱向。
實現(xiàn)網(wǎng)格布局加這句：GridLayoutManager layoutManager = new GridLayoutManager(GridLayoutManager.VERTICAL,3);
其參數(shù)與瀑布相似。
RecyclerView的點擊事件
RecyclerView的所有的點擊事件都由具體的View去注冊。
舉個例子：
...
static class ViewHolder extends RecyclerView.ViewHolder{
ImageView fruitImage;
TextView fruitName;
//定義一個View接收子項的View
View fruitView;
public ViewHolder(View itemView) {
super(itemView);
fruitView = itemView;
fruitImage = (ImageView) itemView.findViewById(R.id.fruit_image);
fruitName = (TextView) itemView.findViewById(R.id.fruit_name);
}
}
...
@Overridepublic
ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
final ViewHolder viewHolder = new ViewHolder(view);
//注冊子項點擊事件
viewHolder.fruitView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int position = viewHolder.getAdapterPosition();
Fruit fruit = mFruitList.get(position);
Toast.makeText(v.getContext(),"you clicked view "+fruit.getName(),Toast.LENGTH_SHORT).show();
}
}
);
//注冊子項中的控件的點擊事件
viewHolder.fruitImage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
int position = viewHolder.getAdapterPosition();
Fruit fruit = mFruitList.get(position);
Toast.makeText(v.getContext(),"you clicked image "+fruit.getName(),Toast.LENGTH_SHORT).show();
}
}
);
return viewHolder;
}
不得不說RecyclerView確實比ListView強大。
