Android常用控件之GridView的蒙板用途和写法

内容

GridView常用语显示照片墙，例如上传图片时当选中一个图片时，会出现一些特殊效果，此时要用到checkBox和蒙板。
布局文件，必须将GridView放在RelativeLayout或FrameLayout，此处用的是最常用的RelativeLayout

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:tools="http://schemas.android.com/tools"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical">

    <GridView
        android:id="@+id/grid_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:numColumns="3">

    </GridView>

</LinearLayout>

GridView的单元项布局grid_item,其中我的蒙板的写法是用一个ImageView设置背景覆盖其他控件，背景默认不显示

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_margin="5dp">

    <CheckBox
        android:id="@+id/item_checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"/>

    <ImageView
        android:id="@+id/item_imageview"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_below="@+id/item_checkbox"
        android:layout_centerHorizontal="true"
        android:src="@mipmap/pk"/>

    <TextView
        android:id="@+id/item_textview"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/item_imageview"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:text="pingguo"/>

    <ImageView
        android:id="@+id/item_image_tint"
        android:layout_width="165dp"
        android:layout_height="150dp"
        android:layout_alignLeft="@+id/item_imageview"
        android:layout_alignTop="@+id/item_checkbox"
        android:background="#55ff0000"
        android:visibility="invisible"/>
</RelativeLayout>

接着建立一个存放单元信息的类Fruit()，其实并不是水果，此处请无视

public class Fruit {
    private String name;
    private int img;

    public Fruit(String name, int img) {
        this.name = name;
        this.img = img;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImg() {
        return img;
    }

    public void setImg(int img) {
        this.img = img;
    }
}

接着建立一个自定义适配器

public class FruitGridAdapter extends BaseAdapter {
    private List<Fruit> mFruits;
    private LayoutInflater mInflater;
    //mCheckBoxManager用于存储所有checkBox是否被选中的状态
    private boolean[] mCheckBoxManager;

    public FruitGridAdapter(List<Fruit> mFruits, LayoutInflater mInflater) {
        this.mFruits = mFruits;
        this.mInflater = mInflater;
        mCheckBoxManager = new boolean[mFruits.size()];
    }

    @Override
    public int getCount() {
        return mFruits.size();
    }

    @Override
    public Object getItem(int position) {
        return position;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        final ViewHolder viewHolder;
        if(convertView==null){
            viewHolder = new ViewHolder();
            convertView = mInflater.inflate(R.layout.grid_item,null);
            viewHolder.imageView = (ImageView) convertView.findViewById(R.id.item_imageview);
            viewHolder.textView = (TextView) convertView.findViewById(R.id.item_textview);
            viewHolder.checkBox = (CheckBox)convertView.findViewById(R.id.item_checkbox);
            viewHolder.tintImageView = (ImageView)convertView.findViewById(R.id.item_image_tint);
            convertView.setTag(viewHolder);
        }else{
            viewHolder = (ViewHolder) convertView.getTag();
        }
        Fruit fruit = mFruits.get(position);
        viewHolder.imageView.setImageResource(fruit.getImg());
        viewHolder.textView.setText(fruit.getName());
        viewHolder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                mCheckBoxManager[position] = isChecked;
                notifyDataSetChanged();//刷新界面信息
            }
        });
        viewHolder.checkBox.setChecked(mCheckBoxManager[position]);
        //如果一个图片对应的checkBox被选中，则让该图的蒙板可见，否则设置为不可见。
        if(mCheckBoxManager[position]){
            viewHolder.tintImageView.setVisibility(View.VISIBLE);
        }else{
            viewHolder.tintImageView.setVisibility(View.INVISIBLE);
        }
        return convertView;
    }

    class ViewHolder{
        ImageView imageView;
        TextView textView;
        CheckBox checkBox;
        ImageView tintImageView;
    }
}

主活动

public class MainActivity extends Activity {
    private List<Fruit> mFruits;
    private LayoutInflater mInflater;
    private GridView gridView;
    private FruitGridAdapter mAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        gridView = (GridView) findViewById(R.id.grid_view);
        mInflater = this.getLayoutInflater();

        mFruits = new ArrayList<>();
        Fruit apple = new Fruit("apple", R.mipmap.a_logo1);
        Fruit pear = new Fruit("pear", R.mipmap.image);
        Fruit pineapple = new Fruit("pineapple", R.mipmap.pk);
        Fruit grape = new Fruit("grape", R.mipmap.ic_launcher);
        for (int i = 0; i < 20; i++) {
            mFruits.add(apple);
            mFruits.add(pear);
            mFruits.add(pineapple);
            mFruits.add(grape);
        }
        mAdapter = new FruitGridAdapter(mFruits,mInflater);
        gridView.setAdapter(mAdapter);
    }
}

结果演示：