Unit3：控件\布局

控件

TextView

<TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/text_view"
        android:text="textView,test 成功"       // 文本
        android:gravity="center"                // 文字居左、右、上、下 
        android:textSize="24sp"                 // 文字大小
        android:textColor="#000"                // 文字颜色
        tools:ignore="MissingConstraints" />

Button

Activity中：

 Button button = findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(ControlActivity.this,"按钮启动",Toast.LENGTH_SHORT).show();;
            }
        });

res中：

<Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="76dp"
        android:text="按钮Button"
        android:textAllCaps="false"      // 大小写分辨
        " />

EditText

Activity中：

 Button button = findViewById(R.id.button);
        final EditText editText = findViewById(R.id.edit_text);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 获取editText的信息 
Toast.makeText(ControlActivity.this,editText.getText().toString(),Toast.LENGTH_SHORT).show();;


            }
        });

res中：

<EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"     
        android:hint="默认提示"           // 默认提示符
        android:maxLines="2"             // 最多占2行
        />

ImageView

Activity中：

更换图像

imageView.setImageResource(R.drawable.banana_pic);

res中：

<ImageView
        android:id="@+id/image_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/apple_pic"   // 添加图片地址
/>

PragressBar

Activity中：

使用setVisibility可以传入
View.VISIBLE(默认，可见）
View.INVISIBLE（不可见，占据位置和大小）
View.GONE（不可见，不占据空间）

                if (progressBar.getVisibility() == View.GONE) {
                    progressBar.setVisibility(View.VISIBLE);
                } else {
                    progressBar.setVisibility(View.GONE);
                }

// 设置进度条
int pro = progressBar.getProgress();
pro = pro + 10;
progressBar.setProgress(pro);

res中：

<ProgressBar
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/progress_bar"
        style="?android:attr/progressBarStyleHorizontal"  // 以进度条方式开启
        android:max="100"            // 进度条最大值100
 />

AlertDialog

Activity中：

                AlertDialog.Builder dialog = new AlertDialog.Builder(ControlActivity.this);
                dialog.setTitle("This is Dialog");
                dialog.setMessage("something Important");
                dialog.setCancelable(false);         // 可否取消
                dialog.setPositiveButton("ok", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        
                    }
                });
                dialog.setNegativeButton("cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {

                    }
                });
                dialog.show();

res中：

ProgressDialog

Activity中：

                ProgressDialog progressDialog = new ProgressDialog(ControlActivity.this);
                progressDialog.setTitle("this is proDialog");
                progressDialog.setMessage("loading ...");
                progressDialog.setCancelable(true);  // 是否可以back消除。如果否，调用ProgressDialog的dismiss()关闭对话框，否则一直存在
                progressDialog.show();

res中：

ListView

1. 基本ListView

Activity中：

  // 首先将需要载入的数据放入data中
      private String[] data = {"Apple","Banana","orange","Watermelon",
        "Pear","Grape","Pineapple","Strawberry","Cherry","Mango","Apple",
        "Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry",
        "Cherry","Mango"};

      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          //        配置适配器：（context，子项布局id(listView的布局，类似容器），数据）；这里将data放入了item_1中
          ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                  MainActivity.this, android.R.layout.simple_expandable_list_item_1,
                  data);
          //        listView装载
          ListView listView = findViewById(R.id.list_view);
          listView.setAdapter(adapter);


      }

res.main_layout中：

添加ListView控件

 <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/list_view"/>

2. 自定义ListView

Activity中：

主Activity中使用自定义的Fruit适配器

public class Main2Activity extends AppCompatActivity {

    private List<Fruit> fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        initFruits();
        FruitAdapter adapter = new FruitAdapter(Main2Activity.this, R.layout.fruit_item, fruitList);
        ListView listView = findViewById(R.id.list_view2);
        listView.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 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.grapes_pic);
            fruitList.add(grape);
            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);
        }
    }
}

自定义Fruit适配器

/**
 * 自定义适配器
 */
public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;

    public FruitAdapter(@NonNull Context context, int resource, @NonNull List<Fruit> objects) {
        super(context, resource, objects);
        resourceId = resource;
    }

    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

        //  为子项加载传入的布局
        //  layoutInflater的from可以构建layoutInflater对象
        //  inflate可以动态加载布局（要加载布局的id，给加载好的布局再添加一个父布局）
        //  第三个参数（只让在父布局中声明layout属性生效，但不为View添加父布局，因为一旦View有了父布局，不能再添加到ListView中）
        View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
        TextView fruitName = view.findViewById(R.id.fruit_name);
        ImageView fruitImage = view.findViewById(R.id.fruit_image);


        Fruit fruit = getItem(position);   // 获取当前项的Fruit实例
        fruitName.setText(fruit.getName());
        fruitImage.setImageResource(fruit.getImageId());

        return view;
    }

自定义Fruit类

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;
    }

}

res.layout中：
/

<ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/list_view2"/>

fruit_layout中：

新建一个fruit_layout，对应fruit中的布局

<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/fruit_name"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="10dp"/>

3. 优化ListView

每次加载getView（）都重新加载一次布局，可以使用convertView参数，将之前加载的布局进行缓存。

  @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {

        View view;
        ViewHolder viewHolder;
        if (convertView == null) {
             view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);

            viewHolder = new ViewHolder();
            viewHolder.fruitName = view.findViewById(R.id.fruit_name);
            viewHolder.fruitImage = view.findViewById(R.id.fruit_image);
            view.setTag(viewHolder);   // 将ViewHolder存储在View中
        } else {
            view = convertView;
            
            viewHolder = (ViewHolder) view.getTag();  // 重新获取ViewHolder
        }
        Fruit fruit = getItem(position);
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());

        return view;
    }

    class ViewHolder {
        ImageView fruitImage;
        TextView fruitName;
    }

解决了重复加载布局的问题，但每次getView（）方法中还是会调用View的findViewById（）获取一次控件实例。

新增一个内部类ViewHolder，用于对控件实例进行缓存。当convertView为空时，创建一个ViewHolder对象，并将控件的实例都存放在ViewHolder里，然后调用View的setTag（）方法，将ViewHolder对象存在View中。
如果不为空，调用View.getTag(),把ViewHolder取出来。控件实例都在缓存中存取。

4. ListView点击事件

Actibity中：

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Fruit fruit = fruitList.get(position);  // 通过position判断用户点击的哪个子项
                Toast.makeText( Main2Activity.this,fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });

RecyclerView

基本启动:

//      1.从数据库中读取数据
        init();
        
//      2.加载适配器
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        FruitAdapter adapter = new FruitAdapter(fruitList);

//      3.布局引入适配器
        RecyclerView recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setLayoutManager(linearLayoutManager);
        recyclerView.setAdapter(adapter);

写新的适配器:

  private List<Fruit> fruitLists;

    public FruitAdapter(List<Fruit> fruitList) {
        fruitLists = fruitList;  // 外部引入数据源
    }



    /**
     * 布局嵌套
     * @param parent
     * @param viewType
     * @return
     */
    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_layout, parent, false);
        ViewHolder viewHolder = new ViewHolder(view);
        return viewHolder;
    }

    /**
     * 缓存器：缓存数据
     */
    static class ViewHolder extends  RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            fruitImage = itemView.findViewById(R.id.fruit_image);
            fruitName = itemView.findViewById(R.id.fruit_name);
        }
    }

    /**
     * 数据写入：将数据库中数据写到缓存
     * @param holder
     * @param position
     */
    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        holder.fruitName.setText(fruitLists.get(position).getFruitName());
        holder.fruitImage.setImageResource(fruitLists.get(position).getFruitImage());

    }

    @Override
    public int getItemCount() {
        return fruitLists.size();
    }

布局

1.LinearLayout

2.FrameLayout

3.RelativeLayout

4.PercentLayout

自定义

1.引入布局

Activity中:

隐藏默认标题栏

     ActionBar actionBar = getSupportActionBar();   // 隐藏标题栏
          if (actionBar != null) {
              actionBar.hide();
          }

res.layout中:

新建自定义title布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#000">

<!--    自定义新的标题框-->
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/button1"
        android:text="返回"
        android:background="#C21B1B"
        android:layout_margin="5dp"
        />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/text"
        android:text="Hello Text"
        android:background="#0C0C0C"
        android:textColor="#fff"
        android:layout_weight="1"
        android:gravity="center"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/button2"
        android:text="进入"
        android:background="#4CAF50"
        android:layout_margin="5dp"
        />

</LinearLayout>

res.main_layout中：

  <include layout="@layout/title"/>

2.自定义控件

Activity中：

新建TitleLayout类继承LearnLayout

/**
 * Title布局，继承自LinearLayout
 */
public class TitleLayout extends LinearLayout {

    public TitleLayout(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

//        将此布局添加到title_layout中
//        from（）方法，创建LayoutInflater对象
//        inflate（int，Root）要加载布局的id，加载好的布局添加父布局
        LayoutInflater.from(context).inflate(R.layout.title,this);

 Button button1 = findViewById(R.id.button1);
        button1.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                Activity context1 = (Activity) getContext();  // getContext（）获取当前运行的上下文，强转成Activity
                context1.finish();
            }
        });

        Button button2 = findViewById(R.id.button2);
        button2.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(getContext(),"进入界面成功",Toast.LENGTH_SHORT).show();
            }
        });
    }
}

res.main_layout中：

使用TitleLayout。此时功能和相同，但是是以控件方式添加，还为控件添加了点击事件

<com.example.unit3_3_self.TitleLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:ignore="MissingConstraints" 
/>