8002117067 徐梓涵 软件工程1702

  • Android中使用非常广泛的控件就是ListView与RecyclerView,这也是学习安卓必知必会的知识点，之前学习的Android第一行代码书时候刚好敲过这个案例，所以本文就使用这两个案例进行实验来说明使用方式。

  • 当时书上是说ListView由于强大的功能，在过去的Android开发中贡献卓越，现在还有很多人使用，不过缺点就是如果不使用一些技巧来对其效率进行提升，那么他的性能就会比较差，而且ListView的扩展性也不够好，只能实现数据的纵向滚动，如果想要使用横向滚动就只能依靠与RecycleView来进行实现了。

  • 本次实验我将会使用ListVIew来显示一个正常的列表，然后使用RecyclerView来显示一个横向布局以及一个瀑布布局。

1. ListView的使用：

ListView的默认界面是显示文本，这是十分单调的，所以我们首先需要对ListVIew的界面进行定制：

  • 我们知道我们显示出来东西到xml对应的界面是需要java中给值映射的，所以我们首先定义一个实体类FruitVIew,这里面的id是用来显示图片的(使用将图片直接放到drawable中),name是用来显示水果名称的：

Fruit.java：

  1. package com.ncu.side_menu;
  3. //水果类
  4. public class Fruit {
  6.     private String name;
  8.     private int imageId;
  10.     public Fruit(String name, int imageId) {
  11.         this.name = name;
  12.         this.imageId = imageId;
  13.     }
  15.     public String getName() {
  16.         return name;
  17.     }
  18.     public int getImageId() {
  19.         return imageId;
  20.     }
  22. }
  • 接下来我们需要为ListView子项定义一个布局,在layout目录下新建一个fruit_item.xml:

fruit_item.xml:

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3.     android:orientation="horizontal"
  4.     android:layout_width="match_parent"
  5.     android:layout_height="match_parent">
  6.     <!--其实这里不是纯正的ListView，而是自己的动态效果来替换ListView-->
  7.     <ImageView
  8.         android:id="@+id/fruit_image"
  9.         android:layout_width="wrap_content"
  10.         android:layout_height="wrap_content" />
  12.     <TextView
  13.         android:id="@+id/fruit_name"
  14.         android:layout_width="wrap_content"
  15.         android:layout_height="wrap_content"
  16.         android:layout_gravity="center_vertical"
  17.         android:layout_marginLeft="10dp" />
  18. </LinearLayout>
  • 在activity_main.xml中我们需要调用一下我们自定义的样式:

activity_main.xml:

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3.     android:layout_width="match_parent"
  4.     android:layout_height="match_parent" >
  6.     <ListView
  7.         android:id="@+id/list_view"
  8.         android:layout_width="match_parent"
  9.         android:layout_height="match_parent" >
  10.     </ListView>
  12. </LinearLayout>
  • 我们知道如果要显示出来必须要一个适配器,如果不是自定义而是原始的listview样式就可以直接使用ArrayAdapter来进行适配,但是由于我们是自定义的一个样式,所以必须要写一个自己的适配器,这个适配器继承于ArrayAdapter,并且将泛型指定为Fruit类,新建FruitAdapter.java:
  • 我们同时在这里对ListView控件进行优化,我们知道如果每次都将布局重新加载一遍,当listview快速滑动时就会成为性能瓶颈,所以我们利用listview中的convertView参数,这是一个将之前的加载好的布局进行缓存的参数.
  • 但是这还是可以继续优化的,我们可以增加一个内部类ViewHolder,对于空间的实例都进行缓存,当convertView为空是我们创建一个ViewHolder将控件实例纯放在其中,这样就不用每次都使用findViewById来获取控件实例了.
  • 如此以来我们就已经将ListVIew的性能优化的不错了.

优化后的FruitAdapter.java:

  1. package com.ncu.side_menu;
  3. import android.content.Context;
  4. import android.view.LayoutInflater;
  5. import android.view.View;
  6. import android.view.ViewGroup;
  7. import android.widget.ArrayAdapter;
  8. import android.widget.ImageView;
  9. import android.widget.TextView;
  11. import java.util.List;
  13. public class FruitAdapter extends ArrayAdapter<Fruit> {
  15.     private int resourceId;
  17.     public FruitAdapter(Context context, int textViewResourceId,
  18.                         List<Fruit> objects) {
  19.         super(context, textViewResourceId, objects);
  20.         resourceId = textViewResourceId;
  21.     }
  23.     @Override
  24.     public View getView(int position, View convertView, ViewGroup parent) {
  25.         Fruit fruit = getItem(position); // 获取当前项的Fruit实例
  26.         View view;
  27.         ViewHolder viewHolder;
  28.         if (convertView == null) {
  29.             view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
  30.             viewHolder = new ViewHolder();
  31.             viewHolder.fruitImage = (ImageView) view.findViewById (R.id.fruit_image);
  32.             viewHolder.fruitName = (TextView) view.findViewById (R.id.fruit_name);
  33.             view.setTag(viewHolder); // 将ViewHolder存储在View中
  34.         } else {
  35.             view = convertView;
  36.             viewHolder = (ViewHolder) view.getTag(); // 重新获取ViewHolder
  37.         }
  38.         viewHolder.fruitImage.setImageResource(fruit.getImageId());
  39.         viewHolder.fruitName.setText(fruit.getName());
  40.         return view;
  41.     }
  43.     class ViewHolder {
  45.         ImageView fruitImage;
  47.         TextView fruitName;
  49.     }
  51. }
  • 最后我们写MainActivity.java,其中的initFruit()方法是加载水果数据,然后创建了一个FruitAdapter适配器传递给ListVIew.
  • 我们可以设置一下列表项的点击事件,使用ListVIew提供的setOnItemClickListener()监听器来监听:

MainActivity.java:

  1. import android.os.Bundle;
  2. import android.view.View;
  3. import android.widget.AdapterView;
  4. import android.widget.ArrayAdapter;
  5. import android.widget.ListView;
  6. import android.widget.Toast;
  8. import java.util.ArrayList;
  9. import java.util.List;
  11. public class MainActivity extends AppCompatActivity {
  13.     private List<Fruit> fruitList = new ArrayList<Fruit>();
  15.     @Override
  16.     protected void onCreate(Bundle savedInstanceState) {
  17.         super.onCreate(savedInstanceState);
  18.         setContentView(R.layout.activity_main);
  19.         initFruits(); // 初始化水果数据
  20.         FruitAdapter adapter = new FruitAdapter(MainActivity.this, R.layout.fruit_item, fruitList);
  22.         ListView listView = (ListView) findViewById(R.id.list_view);
  23.         listView.setAdapter(adapter);//设置显示
  25.         listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
  26.             @Override
  27.             public void onItemClick(AdapterView<?> parent, View view,
  28.                                     int position, long id) {
  29.                 Fruit fruit = fruitList.get(position);
  30.                 Toast.makeText(MainActivity.this, fruit.getName(), Toast.LENGTH_SHORT).show();
  31.             }
  32.         });
  33.     }
  35.     private void initFruits() {
  36.         for (int i = 0; i < 2; i++) {
  37.             Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
  38.             fruitList.add(apple);
  39.             Fruit banana = new Fruit("Banana", R.drawable.banana_pic);
  40.             fruitList.add(banana);
  41.             Fruit orange = new Fruit("Orange", R.drawable.orange_pic);
  42.             fruitList.add(orange);
  43.             Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);
  44.             fruitList.add(watermelon);
  45.             Fruit pear = new Fruit("Pear", R.drawable.pear_pic);
  46.             fruitList.add(pear);
  47.             Fruit grape = new Fruit("Grape", R.drawable.grape_pic);
  48.             fruitList.add(grape);
  49.             Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);
  50.             fruitList.add(pineapple);
  51.             Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);
  52.             fruitList.add(strawberry);
  53.             Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);
  54.             fruitList.add(cherry);
  55.             Fruit mango = new Fruit("Mango", R.drawable.mango_pic);
  56.             fruitList.add(mango);
  57.         }
  58.     }
  60. }

这样我们的第一个项目ListView就大功告成了我们可以显示看一下效果:

  1.                             ![image.png](https://cdn.nlark.com/yuque/0/2020/png/489622/1585840993081-411859fd-3e60-49e0-b612-ae2dbdfb319c.png#align=left&display=inline&height=518&name=image.png&originHeight=1008&originWidth=603&size=131597&status=done&style=none&width=310)

2. RecyclerView的使用:

2.1 RecycleView横向布局显示方式:

我们在ListView的代码上进行一些改动.

  • 首先我们保留ListView中定义的Fruit水果实体类.
  • 然后我们需要导入recycleview需要导入的依赖:

app文件中的build.gradl:

  1. //noinspection GradleCompatible
  2.     implementation 'com.android.support:recyclerview-v7:28.0.0'
  • 由于我们希望横向布局显示,所以采用上面图片下面文字的自定义格式来进行显示:

修改fruit_item.xml:

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3.     android:layout_width="wrap_content"
  4.     android:layout_height="wrap_content"
  5.     android:orientation="vertical">
  6.     <!--其实这里不是纯正的ListView，而是自己的动态效果来替换ListView-->
  8.     <ImageView
  9.         android:id="@+id/fruit_image"
  10.         android:layout_width="155dp"
  11.         android:layout_height="151dp" />
  13.     <TextView
  14.         android:id="@+id/fruit_name"
  15.         android:layout_width="155dp"
  16.         android:layout_height="115dp" />
  18. </LinearLayout>
  • 然后要在调用的xml类中将原来的ListView标签进行修改:

activity_main.xml:

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3.     android:layout_width="match_parent"
  4.     android:layout_height="match_parent">
  6.     <androidx.recyclerview.widget.RecyclerView
  7.         android:id="@+id/recycler_view"
  8.         android:layout_width="match_parent"
  9.         android:layout_height="match_parent" />
  11. </LinearLayout>
  • 首先我们对ViewHolder进行修改,使他继承于RecyclerVIew.ViewHolder,然后在这个类的构造函数中传入一个View参数,这个是RecycleView子项的最外层布局,这样就可以通过findViewById()方法来访问到布局中的图像以及文本实例.
  • FruitAdapter类中的构造函数将需要显示的数据传递进来,并且不止给mFruitList,然后操作就在这个上面进行.
  • FruitAdapter继承于RecyclerView.Adapter,所以必须要重写三个方法:

    onCreateViewHolder()函数用来创建ViewHolder实例的. onCreateViewHolder()函数用来给RecycleView子项进行数据赋值的 getItem返回有多少项的.

FruitAdapter.java:

  1. package com.ncu.recyclerview;
  2. import android.view.LayoutInflater;
  3. import android.view.View;
  4. import android.view.ViewGroup;
  5. import android.widget.ImageView;
  6. import android.widget.TextView;
  7. import android.widget.Toast;
  9. import androidx.recyclerview.widget.RecyclerView;
  11. import java.util.List;
  13. public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder>{
  15.     private List<Fruit> mFruitList;
  17.     static class ViewHolder extends RecyclerView.ViewHolder {
  18.         View fruitView;
  19.         ImageView fruitImage;
  20.         TextView fruitName;
  22.         public ViewHolder(View view) {
  23.             super(view);
  24.             fruitView = view;
  25.             fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
  26.             fruitName = (TextView) view.findViewById(R.id.fruit_name);
  27.         }
  28.     }
  30.     public FruitAdapter(List<Fruit> fruitList) {
  31.         mFruitList = fruitList;
  32.     }
  34.     @Override
  35.     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
  36.         View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);
  37.         final ViewHolder holder = new ViewHolder(view);
  38.         holder.fruitView.setOnClickListener(new View.OnClickListener() {
  39.             @Override
  40.             public void onClick(View v) {
  41.                 int position = holder.getAdapterPosition();
  42.                 Fruit fruit = mFruitList.get(position);
  43.                 Toast.makeText(v.getContext(), "you clicked view " + fruit.getName(), Toast.LENGTH_SHORT).show();
  44.             }
  45.         });
  46.         holder.fruitImage.setOnClickListener(new View.OnClickListener() {
  47.             @Override
  48.             public void onClick(View v) {
  49.                 int position = holder.getAdapterPosition();
  50.                 Fruit fruit = mFruitList.get(position);
  51.                 Toast.makeText(v.getContext(), "you clicked image " + fruit.getName(), Toast.LENGTH_SHORT).show();
  52.             }
  53.         });
  54.         holder.fruitName.setOnClickListener(new View.OnClickListener() {
  55.             @Override
  56.             public void onClick(View v) {
  57.                 int position = holder.getAdapterPosition();
  58.                 Fruit fruit = mFruitList.get(position);
  59.                 Toast.makeText(v.getContext(), "you clicked name " + fruit.getName(), Toast.LENGTH_SHORT).show();
  60.             }
  61.         });
  62.         return holder;
  63.     }
  65.     @Override
  66.     public void onBindViewHolder(ViewHolder holder, int position) {
  67.         Fruit fruit = mFruitList.get(position);
  68.         holder.fruitImage.setImageResource(fruit.getImageId());
  69.         holder.fruitName.setText(fruit.getName());
  70.     }
  72.     @Override
  73.     public int getItemCount() {
  74.         return mFruitList.size();
  75.     }
  77. }
  • 还剩最后一步就是完成MainActivity,与ListView不同的是RecycleView可以通过布局管理器LinearLayoutManager来控制我们的滑动方向,首先创建一个LinearLayoutManager对象,然后设置我们需要布局的方向,最后让我们的列表调用setLayoutMany传入参数:recyclerView.setLayoutManager(linearLayoutManager);

MainActivity.java:

  1. package com.ncu.recyclerview;
  3. import androidx.appcompat.app.AppCompatActivity;
  4. import androidx.recyclerview.widget.LinearLayoutManager;
  5. import androidx.recyclerview.widget.RecyclerView;
  6. import androidx.recyclerview.widget.StaggeredGridLayoutManager;
  8. import android.os.Bundle;
  9. import android.widget.LinearLayout;
  11. import java.util.ArrayList;
  12. import java.util.List;
  13. import java.util.Random;
  15. public class MainActivity extends AppCompatActivity {
  17.     private List<Fruit> fruitList = new ArrayList<Fruit>();
  19.     @Override
  20.     protected void onCreate(Bundle savedInstanceState) {
  21.         super.onCreate(savedInstanceState);
  22.         setContentView(R.layout.activity_main);
  23.         initFruits();
  24.         RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
  25.         LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
  26.         linearLayoutManager.setOrientation(RecyclerView.HORIZONTAL);
  27.         recyclerView.setLayoutManager(linearLayoutManager);
  28.         FruitAdapter adapter = new FruitAdapter(fruitList);
  29.         recyclerView.setAdapter(adapter);
  30.     }
  32.     private void initFruits() {
  33.         for (int i = 0; i < 2; i++) {
  34.             Fruit apple = new Fruit(getRandomLengthName("Apple"), R.drawable.apple_pic);
  35.             fruitList.add(apple);
  36.             Fruit banana = new Fruit(getRandomLengthName("Banana"), R.drawable.banana_pic);
  37.             fruitList.add(banana);
  38.             Fruit orange = new Fruit(getRandomLengthName("Orange"), R.drawable.orange_pic);
  39.             fruitList.add(orange);
  40.             Fruit watermelon = new Fruit(getRandomLengthName("Watermelon"), R.drawable.watermelon_pic);
  41.             fruitList.add(watermelon);
  42.             Fruit pear = new Fruit(getRandomLengthName("Pear"), R.drawable.pear_pic);
  43.             fruitList.add(pear);
  44.             Fruit grape = new Fruit(getRandomLengthName("Grape"), R.drawable.grape_pic);
  45.             fruitList.add(grape);
  46.             Fruit pineapple = new Fruit(getRandomLengthName("Pineapple"), R.drawable.pineapple_pic);
  47.             fruitList.add(pineapple);
  48.             Fruit strawberry = new Fruit(getRandomLengthName("Strawberry"), R.drawable.strawberry_pic);
  49.             fruitList.add(strawberry);
  50.             Fruit cherry = new Fruit(getRandomLengthName("Cherry"), R.drawable.cherry_pic);
  51.             fruitList.add(cherry);
  52.             Fruit mango = new Fruit(getRandomLengthName("Mango"), R.drawable.mango_pic);
  53.             fruitList.add(mango);
  54.         }
  55.     }
  57.     private String getRandomLengthName(String name) {
  58.         Random random = new Random();
  59.         int length = random.nextInt(20) + 1;
  60.         StringBuilder builder = new StringBuilder();
  61.         for (int i = 0; i < length; i++) {
  62.             builder.append(name);
  63.         }
  64.         return builder.toString();
  65.     }
  67. }

这样就大功告成了,我们看一下显示的效果:

  1.                                                 ![image.png](https://cdn.nlark.com/yuque/0/2020/png/489622/1585891783728-e03bc660-6618-477d-8468-398bd1fe61d6.png#align=left&display=inline&height=472&name=image.png&originHeight=673&originWidth=379&size=69298&status=done&style=none&width=266)

2.2 RecycleView瀑布布局显示方式:

说是瀑布布局,其实是通过布局管理器_StaggeredGridLayoutManag_er进行管理,本质类似于GridVIew的布局风格,加上文字内容多少不一使得显示的有层次感觉.

  • 首先我们需要设定列表中文字的高度随着大小:

fruite_item.xml:

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  3.     android:layout_width="wrap_content"
  4.     android:layout_height="wrap_content"
  5.     android:orientation="vertical">
  6.     <!--其实这里不是纯正的ListView，而是自己的动态效果来替换ListView-->
  8.     <ImageView
  9.         android:id="@+id/fruit_image"
  10.         android:layout_width="154dp"
  11.         android:layout_height="150dp" />
  13.     <TextView
  14.         android:id="@+id/fruit_name"
  15.         android:layout_width="154dp"
  16.         android:layout_height="wrap_content" />
  18. </LinearLayout>
  • 然后我们在MainActivity中换一种布局管理器StaggeredGridLayoutManager来管理.
  • 设置滑动方向向下,并且一行只能有三个:

MainActivity.java:

  1. package com.ncu.recyclerview;
  3. import androidx.appcompat.app.AppCompatActivity;
  4. import androidx.recyclerview.widget.LinearLayoutManager;
  5. import androidx.recyclerview.widget.RecyclerView;
  6. import androidx.recyclerview.widget.StaggeredGridLayoutManager;
  8. import android.os.Bundle;
  9. import android.widget.LinearLayout;
  11. import java.util.ArrayList;
  12. import java.util.List;
  13. import java.util.Random;
  15. public class MainActivity extends AppCompatActivity {
  17.     private List<Fruit> fruitList = new ArrayList<Fruit>();
  19.     @Override
  20.     protected void onCreate(Bundle savedInstanceState) {
  21.         super.onCreate(savedInstanceState);
  22.         setContentView(R.layout.activity_main);
  23.         initFruits();
  24.         RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
  25.             StaggeredGridLayoutManager layoutManager = new
  26.                 StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
  27.         /*
  28.         LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
  29.         linearLayoutManager.setOrientation(RecyclerView.HORIZONTAL);
  30.         */
  31.         recyclerView.setLayoutManager(layoutManager);
  32.         FruitAdapter adapter = new FruitAdapter(fruitList);
  33.         recyclerView.setAdapter(adapter);
  34.     }
  36.     private void initFruits() {
  37.         for (int i = 0; i < 2; i++) {
  38.             Fruit apple = new Fruit(getRandomLengthName("Apple"), R.drawable.apple_pic);
  39.             fruitList.add(apple);
  40.             Fruit banana = new Fruit(getRandomLengthName("Banana"), R.drawable.banana_pic);
  41.             fruitList.add(banana);
  42.             Fruit orange = new Fruit(getRandomLengthName("Orange"), R.drawable.orange_pic);
  43.             fruitList.add(orange);
  44.             Fruit watermelon = new Fruit(getRandomLengthName("Watermelon"), R.drawable.watermelon_pic);
  45.             fruitList.add(watermelon);
  46.             Fruit pear = new Fruit(getRandomLengthName("Pear"), R.drawable.pear_pic);
  47.             fruitList.add(pear);
  48.             Fruit grape = new Fruit(getRandomLengthName("Grape"), R.drawable.grape_pic);
  49.             fruitList.add(grape);
  50.             Fruit pineapple = new Fruit(getRandomLengthName("Pineapple"), R.drawable.pineapple_pic);
  51.             fruitList.add(pineapple);
  52.             Fruit strawberry = new Fruit(getRandomLengthName("Strawberry"), R.drawable.strawberry_pic);
  53.             fruitList.add(strawberry);
  54.             Fruit cherry = new Fruit(getRandomLengthName("Cherry"), R.drawable.cherry_pic);
  55.             fruitList.add(cherry);
  56.             Fruit mango = new Fruit(getRandomLengthName("Mango"), R.drawable.mango_pic);
  57.             fruitList.add(mango);
  58.         }
  59.     }
  61.     private String getRandomLengthName(String name) {
  62.         Random random = new Random();
  63.         int length = random.nextInt(20) + 1;
  64.         StringBuilder builder = new StringBuilder();
  65.         for (int i = 0; i < length; i++) {
  66.             builder.append(name);
  67.         }
  68.         return builder.toString();
  69.     }
  71. }

我们看一下显示出来的效果:

  1.                                                         ![image.png](https://cdn.nlark.com/yuque/0/2020/png/489622/1585894871064-9aefc5f7-96c2-49a4-8296-10b9e231516d.png#align=left&display=inline&height=410&name=image.png&originHeight=675&originWidth=379&size=192040&status=done&style=none&width=230)

以上就是本周的学习报告.