Android ArrayAdapter 源码查看 深入了解

问题

继承ArrayAdapter构造自己类时候，我是这样写的

public class IconAdapter extends ArrayAdapter<Icon> {
    private List<Icon> images;
    private int resourceId;
    private Context context;

    public IconAdapter(Context context, int resource, List<Icon> images) {
        super(context, resource, images);
        this.context = context;
        this.resourceId = resourceId;
        this.images = images;
    }

发现网上有些代码只是这样

public IconAdapter(Context context, int resource, List<Icon> images) {
        super(context, resource, images);   
        this.resourceId = resourceId;  
    }

我疑惑, 不需要一个 List 来保存数据吗?

查看ArrayAdapter源代码

为了突出重点, 下面只列出我们需要的源代码

public class ArrayAdapter<T> extends BaseAdapter implements Filterable, ThemedSpinnerAdapter {
   private List<T> mObjects;
   public ArrayAdapter(Context context, @LayoutRes int resource, @IdRes int textViewResourceId,
          @NonNull List<T> objects) {
      mContext = context;
      mInflater = LayoutInflater.from(context);
      mResource = mDropDownResource = resource;
      mObjects = objects;
      mFieldId = textViewResourceId;
  }

注意到ArrayAdapter其实源代码自带了 mObjects 集合变量

如何获取集合里的某个元素

本来我是这样做的

Icon icon = images.get(position); 

后来发现源代码里有 getItem 方法

public T getItem(int position) {
    return mObjects.get(position);
}

获取 context

我本来是打算定义一个变量 context, 在构造函数里面初始化

private Context context;
public IconAdapter(Context context, int resource, List<Icon> images, int resourceId) {
    super(context, resource, images);
    this.context = context;
    this.resourceId = resourceId;
    this.images = images;
}

然后其他方法使用这个变量就行,
LayoutInflater.from(context).inflate(resourceId, parent)
发现也是多虑了, 源代码已经实现了

public Context getContext() {
    return mContext;
}

附上最终的public class IconAdapter extends ArrayAdapter<Icon>源代码

package com.example.tomchen.testlistview;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.List;

/** * Created by tomchen on 9/1/15. */
public class IconAdapter extends ArrayAdapter<Icon> {
    private int resourceId;


    public IconAdapter(Context context, int resource, List<Icon> icons) {
        super(context, resource, icons);
        this.resourceId = resource;
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Icon icon = getItem(position);
        View view;
        if (convertView == null) {
            view = LayoutInflater.from(getContext()).inflate(resourceId, null);
        } else {
            view = convertView;
        }
        ImageView image = (ImageView) view.findViewById(R.id.icon);
        image.setImageResource(icon.getImageId());
        TextView text = (TextView) view.findViewById(R.id.text);
        text.setText(icon.getName());
        return view;
    }
}