Java 如何在回收器视图适配器中获取上下文

How to get a context in a recycler view adapter

提问by Stranger B.

I'm trying to use picasso library to be able to load url to imageView, but I'm not able to get the contextto use the picasso library correctly.

我正在尝试使用 picasso 库来将 url 加载到 imageView，但我无法context正确使用 picasso 库。

public class FeedAdapter extends RecyclerView.Adapter<FeedAdapter.ViewHolder> {
    private List<Post> mDataset;



    // Provide a reference to the views for each data item
    // Complex data items may need more than one view per item, and
    // you provide access to all the views for a data item in a view holder
    public class ViewHolder extends RecyclerView.ViewHolder {
        // each data item is just a string in this case
        public TextView txtHeader;
        public ImageView pub_image;
        public ViewHolder(View v) {
            super(v);
            txtHeader = (TextView) v.findViewById(R.id.firstline);
            pub_image = (ImageView) v.findViewById(R.id.imageView);


        }
    }




    // Provide a suitable constructor (depends on the kind of dataset)
    public FeedAdapter(List<Post> myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public FeedAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.feedholder, parent, false);
        // set the view's size, margins, paddings and layout parameters
        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element

        holder.txtHeader.setText(mDataset.get(position).getPost_text());

        Picasso.with(this.context).load("http://i.imgur.com/DvpvklR.png").into(holder.pub_image);


    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.size();
    }

}

采纳答案by pelotasplus

You have a few options here:

您在这里有几个选择：

1. Pass Contextas an argument to FeedAdapter and keep it as class field
2. Use dependency injection to inject Contextwhen you need it. I strongly suggest reading about it. There is a great tool for that -- Daggerby Square

3. Get it from any Viewobject. In your case this might work for you:

   holder.pub_image.getContext()

   As pub_imageis a ImageView.

1. Context作为参数传递给 FeedAdapter 并将其保留为类字段
2. Context需要时使用依赖注入进行注入。我强烈建议阅读它。有一个很好的工具——Daggerby Square

3. 从任何View对象获取它。在您的情况下，这可能对您有用：

   holder.pub_image.getContext()

   就像pub_image一个ImageView.

回答by blockwala

Create a constructor of FeedAdapter :

创建 FeedAdapter 的构造函数：

Context context; //global
public FeedAdapter(Context context)
{
   this.context = context;  
}

and in Activity

并在活动中

FeedAdapter obj = new FeedAdapter(this);

回答by Blue_Alien

First globally declare

首先全局声明

Context mContext;

Context mContext;

pass context with the constructor, by modifying it.

通过修改构造函数传递上下文。

public FeedAdapter(List<Post> myDataset, Context context) {
    mDataset = myDataset;
    this.mContext = context;
}

then use the mContextwhereever you need it

然后在mContext任何需要的地方使用

回答by AKT

First add a global variable

首先添加一个全局变量

Context mContext;

Then change your constructor to this

然后将您的构造函数更改为此

public FeedAdapter(Context context, List<Post> myDataset) {
    mContext = context;
    mDataset = myDataset;
}

The pass your context when creating the adapter.

创建适配器时传递您的上下文。

FeedAdapter myAdapter = new FeedAdapter(this,myDataset);

回答by Farhad Navayazdan

You can add global variable:

您可以添加全局变量：

private Context context;

then assign the context from here:

然后从这里分配上下文：

@Override
public FeedAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,int viewType) {
    // create a new view
    View v=LayoutInflater.from(parent.getContext()).inflate(R.layout.feedholder, parent, false);
    // set the view's size, margins, paddings and layout parameters
    ViewHolder vh = new ViewHolder(v);
    // set the Context here 
    context = parent.getContext();
    return vh;
}

Happy Codding :)

快乐编码:)

回答by Ahmad Aghazadeh

You can use pub_image context (holder.pub_image.getContext()) :

您可以使用 pub_image 上下文 ( holder.pub_image.getContext()) ：

@Override
public void onBindViewHolder(ViewHolder ViewHolder, int position) {

    holder.txtHeader.setText(mDataset.get(position).getPost_text());

    Picasso.with(holder.pub_image.getContext()).load("http://i.imgur.com/DvpvklR.png").into(holder.pub_image);


}

回答by Arpit Patel

You can use like this view.getContext()

您可以像这样使用view.getContext()

Example

例子

holder.tv_room_name.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            Toast.makeText(v.getContext(), "", Toast.LENGTH_SHORT).show();


        }
    });

回答by u7962780

you can use this:

你可以使用这个：

itemView.getContext()

回答by Maciej Beimcik

Short answer:

简短的回答：

Context context;

@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
    super.onAttachedToRecyclerView(recyclerView);
    context = recyclerView.getContext();
}

Explanation why other answers are not great:

解释为什么其他答案不是很好：

1. Passing Contextto the adapter is completely unnecessary, since RecyclerViewyou can access it from inside the class
2. Obtaining Contextat ViewHolderlevel means that you do it every time you bind or create a ViewHolder. You duplicate operations.
3. I don't think you need to worry about any memory leak. If your adapter lingers outside your Activitylifespan (which would be weird) then you already have a leak.

1. 传递Context给适配器是完全没有必要的，因为RecyclerView您可以从类内部访问它
2. Context在ViewHolder级别获取意味着您每次绑定或创建ViewHolder. 您重复操作。
3. 我认为您无需担心任何内存泄漏。如果您的适配器在您的Activity使用寿命之外徘徊（这很奇怪），那么您已经泄漏了。

回答by Marcos vitouley

You can define:

您可以定义：

Context ctx; 

And on onCreateinitialise ctxto:

并onCreate初始化ctx为：

ctx=parent.getContext(); 

Note: Parent is a ViewGroup.

注意：Parent 是一个 ViewGroup。