标签：cli sdn double instance dem 实现 exti protected 固定
ListView的基本应用因为要展示大量数据，这就涉及到将数据注入到view中的过程。
不过，数组中的数据是无法直接传递到view的，这需要借助适配器来实现。
Android是完全遵循MVC模式设计的框架,Activity是Controller,layout是View，因为layout五花八门,很多数据都不能直接绑定上去,所以Android引入了Adapter这个机制作为复杂数据的展示的转换载体,所以各种Adapter只不过是转换的方式和能力不一样而已。
几种常用的Adapter:
展示简单的字符串ListView
public class ListActivity extends BaseActivity {
private String[] data = { "Apple","Banana","Orange","WaterMelon",
"Pear","Grape","Pineapple","Strawberry","Strawberry","Strawberry","Strawberry",
"Strawberry","Strawberry","Strawberry","Strawberry","Strawberry","Strawberry","Strawberry"
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
ArrayAdapter<String> adapter = new ArrayAdapter<String>(
ListActivity.this, android.R.layout.simple_list_item_1,data
);
ListView listView = (ListView) findViewById(R.id.list_view);
listView.setAdapter(adapter);
}
}
上文中的android.R.layout.simple_list_item_1用的是android自带的布局，如果要自定义一个View，需要手写一个item的布局，然后写一个适配器，需要重写构造函数和getView方法。
public class FruitAdapter extends ArrayAdapter<Fruit> {
private int resourceId;
public FruitAdapter(Context context, int textViewResourceId,
List<Fruit> objects) {
super(context, textViewResourceId, objects);
resourceId = textViewResourceId;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position); // 获取当前项的Fruit实例
View view;
ViewHolder viewHolder;
if (convertView == null) {
// 加载布局，listitem不需要添加父布局
view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
// new一个viewHolder，拥有对view中各个控件的引用
viewHolder = new ViewHolder();
viewHolder.fruitImage = (ImageView) view.findViewById (R.id.fruit_image);
viewHolder.fruitName = (TextView) view.findViewById (R.id.fruit_name);
view.setTag(viewHolder); // 将ViewHolder存储在View中
} else {
view = convertView;
viewHolder = (ViewHolder) view.getTag(); // 重新获取ViewHolder
}
viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());
return view;
}
class ViewHolder {
ImageView fruitImage;
TextView fruitName;
}
}
这里优化，当convertView为空的时候才去加载布局，创建view。如果不为空则直接用缓存中的view实例convertView，就省去了findbyview这种创建view实例的过程。通过获取viewHolder得到view实例中各个控件的引用，因为数据是不能复用的，所以需要重新set相关控件的数据。
关于缓存：https://blog.csdn.net/Double2hao/article/details/49077739
调用比较简单
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
initFruits();
FruitAdapter adapter = new FruitAdapter(ListActivity.this,R.layout.fruit_item,fruitList);
ListView listView = (ListView) findViewById(R.id.list_view);
listView.setAdapter(adapter);
}
private void initFruits() {
for (int i = 0; i < 10; ++i) {
Fruit apple = new Fruit("Apple",R.drawable.img_1);
fruitList.add(apple);
Fruit banana = new Fruit("banana",R.drawable.img_2);
fruitList.add(banana);
}
}
RecyclerView的基本应用ListView是有很多缺点的，因为效率不高所以需要加很多优化。
将上文的demo改成使用RecyclerView实现：
RecyclerView.Adapter，并将泛型指定为新适配器的ViewHolder。RecyclerView.ViewHolderRecyclerView子项最外层布局，于是就可以通过findViewById的方法来获取布局中的ImageView和TextView的实例。RecyclerView.Adapter，所以必须重写onCreateViewHolder，onBindViewHolder和getItemCountpublic class RecyclerFruitAdapter extends RecyclerView.Adapter<RecyclerFruitAdapter.ViewHolder> {
private List<Fruit> mFruitList; // 数据源，存实例对象
public RecyclerFruitAdapter(List<Fruit> fruitList) {
this.mFruitList = fruitList;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
final ViewHolder viewHolder = new ViewHolder(view);
viewHolder.fruitView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Fruit fruit = mFruitList.get(viewHolder.getAdapterPosition());
Toast.makeText(v.getContext(), "you clicked view " + fruit.getName(), Toast.LENGTH_SHORT).show();
}
});
viewHolder.fruitImage.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Fruit fruit = mFruitList.get(viewHolder.getAdapterPosition());
Toast.makeText(v.getContext(), "you clicked image " + fruit.getName(), Toast.LENGTH_SHORT).show();
}
});
return viewHolder;
}
@Override
public void onBindViewHolder(@NonNull 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();
}
static class ViewHolder extends RecyclerView.ViewHolder {
View fruitView;
ImageView fruitImage;
TextView fruitName;
public ViewHolder(@NonNull View itemView) {
super(itemView);
fruitView = itemView;
fruitImage = (ImageView) itemView.findViewById(R.id.fruit_image);
fruitName = (TextView) itemView.findViewById(R.id.fruit_name);
}
}
}
onCreateViewHolder：是用来创建ViewHolder实例的，在这里将item布局加载，然后将加载好的view传入holder的构造函数中创建ViewHolder实例。onBindViewHolder：是对item的数据进行赋值，会在每个子项被滚动到屏幕内的时候执行。通过position参数可以得到当前项的数据，即fruit实例。然后再对保存的ViewHolder中的fruitImage和fruitName对象赋值。(省去获得实例的过程)getItemCount：返回RecycleView的长度 @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recycle);
initFruits();
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
RecyclerFruitAdapter fruitAdapter = new RecyclerFruitAdapter(fruitList);
recyclerView.setAdapter(fruitAdapter);
}
这里多了一个LayoutManager，用于指定RecyclerView的布局方式，这里使用LinearLayoutManager就是线性布局的意思。
简单实现的xml如下：
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
tools:context=".Recycler.RecycleActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</androidx.constraintlayout.widget.ConstraintLayout>
<?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"> #一个item宽度刚好是父布局的宽度，高度则用当前刚刚好包住里面的内容
<ImageView
android:id="@+id/fruit_image"
android:layout_height="80dp"
android:layout_width="100dp"
/>
<TextView
android:id="@+id/fruit_name"
android:layout_marginLeft="8dp"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp" />
</LinearLayout>
首先要修改fruit_item，将每个item的宽度设成一个固定的值，并将item里水平布局改成垂直的。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="100dp"
android:layout_height="wrap_content">
<ImageView
android:id="@+id/fruit_image"
android:layout_height="50dp"
android:layout_width="80dp"
/>
<TextView
android:id="@+id/fruit_name"
android:layout_marginTop="10dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal" />
</LinearLayout>
在之前的调用基础上，加上LinearLayoutManager的setOrientatian方法来设置布局的排列方向。默认是纵向排列，传入LinearLayoutManager.HORIZONTAL表示让布局横向排列。
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
RecyclerView提供了GridLayoutManager和StaggeredGridLayoutManager两种内置的布局排列方式，前者可以实现网格布局，后者可以用于实现瀑布流布局。
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_margin="10dp"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<ImageView
android:id="@+id/fruit_image"
android:layout_height="100dp"
android:layout_width="match_parent"
/>
<TextView
android:id="@+id/fruit_name"
android:layout_marginTop="10dp"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="left" />
</LinearLayout>
这里因为每个item的宽度可以通过列数来自动适配，不是一个固定值，所以match_parent就行
在调用时也比较简单，这里为了凸出效果，文字设定为随机长度
public class RecycleActivity extends AppCompatActivity {
private List<Fruit> fruitList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recycle);
initFruits();
RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(2,StaggeredGridLayoutManager.VERTICAL);
recyclerView.setLayoutManager(layoutManager);
RecyclerFruitAdapter fruitAdapter = new RecyclerFruitAdapter(fruitList);
recyclerView.setAdapter(fruitAdapter);
}
private void initFruits() {
for (int i = 0; i < 10; ++i) {
Fruit apple = new Fruit(getRandomLengthName("Apple"),R.drawable.img_1);
fruitList.add(apple);
Fruit banana = new Fruit(getRandomLengthName("banana"),R.drawable.img_2);
fruitList.add(banana);
}
}
private String getRandomLengthName(String name) {
Random random = new Random();
int length = random.nextInt(20) + 1;
StringBuilder builder = new StringBuilder();
for (int i = 0; i < length; i++) {
builder.append(name);
}
return builder.toString();
}
}
标签：cli sdn double instance dem 实现 exti protected 固定
原文地址：https://www.cnblogs.com/smallocean/p/14448826.html
