58

在我在 Internet 上找到的许多代码示例中，context都是在适配器的构造函数中获得的。

此上下文用于获取方法inflater中的视图膨胀getView。

我的问题是，当它可以像这样轻松获得时，为什么还要麻烦在构造函数中获取上下文

        LayoutInflater inflater;
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if(inflater == null){
            Context context = parent.getContext();
            inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            }
            ...
            ...

            return convertView;
        }

还有什么理由不使用上述方法，因为到目前为止我在使用它时没有遇到任何问题。

4

5 回答 5

41

Obtaining the Context in the constructor has (at least) three advantages:

  1. You only do it once, not every time, getView() is called.
  2. You can use it for other purposes too, when needed.
  3. It also works, when parent is null.

However, if you don't have any problems with your solution, you might as well stick to it.

于 2012-08-27T09:08:06.153 回答
4

Here is an example:

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View view = convertView;
    Holder holder;
    if (view == null) {
        view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_job, parent, false);
        holder = new Holder(view, this);
        view.setTag(holder);
    } else {
        holder = (Holder) view.getTag();
    }

    holder.parse(getItem(position), position);
    return view;
}

public class Holder {

    @Bind(R.id.type)
    TextView type;
    @Bind(R.id.date_time)
    TextView dateTime;
    @Bind(R.id.grade)
    TextView grade;

    public Holder(View view) {
        ButterKnife.bind(this, view);
    }

    public void parse(final GetGradeHistoryResponse.GradeHistory item) {
        if (item.grade < 0) {
            grade.setTextColor(App.getInstance()
                    .getResources().getColor(R.color.withdraw_status));
            grade.setText(String.valueOf(item.grade));
        } else {
            grade.setTextColor(App.getInstance()
                    .getResources().getColor(R.color.primary));
            grade.setText("+" + String.valueOf(item.grade));
        }

        type.setText(item.type);
        dateTime.setText(item.datetime);
    }
}

You can get context by view.getContext() in the Holder

于 2015-12-18T08:28:30.520 回答
3

Just simple like this!!

class RecentlyAdapter(var data: List<String>) : Adapter<RecentlyAdapter.HomeViewHolder>() {

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): HomeViewHolder {
    val inflater = LayoutInflater.from(parent.context)
    val view = inflater.inflate(R.layout.card_recently_played, parent, false)
    return HomeViewHolder(view)
}

override fun getItemCount(): Int {
    return data.size
}

override fun onBindViewHolder(holder: HomeViewHolder, position: Int) {

}

class HomeViewHolder(itemView: View): ViewHolder(itemView) {
    init {
        itemView.setOnClickListener {
            val intent = Intent(itemView.context, MusicPlayerActivity::class.java)
            var context = itemView.context
            context.startActivity(intent)
        }
    }
}

}

To get context use itemView.context

于 2019-06-21T08:20:30.077 回答
2

如果有人将创建一个用于BaseAdapter在某处存储视图的类（并且，也许稍后会将它们附加到父级）怎么办？在这种情况下parent可能是null。

这不是什么大问题，自己决定什么更好。

例如：

public class MockWithAdapter{

    private BaseAdapter mAdapter;

    public MockWithAdapter(BaseAdapter adapter){
        mAdapter = adapter;
    }

    public List<View> mock(){
        int size = mAdapter.getCount();
        List<View> views = new ArrayList(size);
        for(int i=0; i<size; i++)
            views.add(mAdapter.getView(i, null, null));

        return views;
    }
}

然后你可以随心所欲地使用这个视图：

MockWithAdapter m = new MockWithAdapter(adapter);
ListView lv = new ListView(context);
for(View v : m.mock)
    lv.addView(v);
于 2012-08-27T07:30:54.747 回答
0

Yes but if you need any activity reference like for example dialog alert you cannot use context reference , therefore constructor should receive activity reference from calling Activity/Fragment

于 2020-02-18T11:19:53.193 回答