Need an example about RecyclerView.Adapter.notifyItemChanged(int position, Object payload)

问题:

First, sorry about my English. According to RecyclerView documentation about medthod notifyItemChanged(int position, Object payload)

Notify any registered observers that the item at position has changed with an optional payload object.

I don't understand how to use second paramenter payload in this method. I have searched many document about "payload" but everything was ambiguous.

So, If you know about this method, please show me a clear example about it. Thank you very much.

回答1:

Check out this sample code that demonstrates the feature. It's a RecyclerView that calls notifyItemChanged(position, payload) when the item at position position is clicked. You can verify that onBindViewHolder(holder, position, payload) was called by looking for the logcat statement.

Make sure you are using at least version 23.1.1 of the support libraries, like so:

dependencies {     compile fileTree(dir: 'libs', include: ['*.jar'])     compile 'com.android.support:appcompat-v7:23.1.1'     compile 'com.android.support:recyclerview-v7:23.1.1'     compile 'com.android.support:cardview-v7:23.1.1' } 

HelloActivity.java

package com.formagrid.hellotest;  import android.app.Activity; import android.os.Bundle; import android.support.v7.widget.CardView; import android.support.v7.widget.DefaultItemAnimator; import android.support.v7.widget.LinearLayoutManager; import android.support.v7.widget.RecyclerView; import android.util.Log; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView;  import java.util.List;  public class HelloActivity extends Activity {      private RecyclerView mRecyclerView;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);         mRecyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));         mRecyclerView.setAdapter(new HelloAdapter());         DefaultItemAnimator animator = new DefaultItemAnimator() {             @Override             public boolean canReuseUpdatedViewHolder(RecyclerView.ViewHolder viewHolder) {                 return true;             }         };         mRecyclerView.setItemAnimator(animator);     }      private static class HelloAdapter extends RecyclerView.Adapter {          public class HelloViewHolder extends RecyclerView.ViewHolder {              public TextView textView;              public HelloViewHolder(CardView cardView) {                 super(cardView);                 textView = (TextView) cardView.findViewById(R.id.text_view);             }          }          @Override         public HelloViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {             CardView cardView = (CardView) LayoutInflater.from(parent.getContext()).inflate(                     R.layout.card_item, parent, false);             return new HelloViewHolder(cardView);         }          @Override         public void onBindViewHolder(HelloViewHolder holder, int position) {             bind(holder);         }          @Override         public void onBindViewHolder(HelloViewHolder holder, int position, List

activity_main.xml

card_item.xml

回答2:

If you want to update not all holder View but just part of it, this method is what you need.

Image that you have following ViewHolder

public class ViewHolder extends RecyclerView.ViewHolder {         public final TextView tvName;         public final TextView tvScore;          public ViewHolder(View view) {             super(view);             tvName = (TextView) view.findViewById(R.id.tv_name);             tvScore = (TextView) view.findViewById(R.id.tv_score);         }      } 

And somewhere in your code you call adapter to update single TextView - tvScore

mRecyclerViewAdapter.notifyItemChanged(position, new Integer(4533)); 

[...]

onBindViewHolder(ViewHolder holder, int position, List payloads) catches callback at first. If payloads doesn't match your requirements you have to obligatory call super class super.onBindViewHolder(holder,position, payloads); which trigger onBindViewHolder(ViewHolder holder, int position) for other cases.

     // Update only part of ViewHolder that you are interested in      // Invoked before onBindViewHolder(ViewHolder holder, int position)         @Override         public void onBindViewHolder(ViewHolder holder, int position, List

回答3:

You can pass in an "optional payload object" when you just want to perform a partial update to the data in the ViewHolder when the onBindViewHolder method is called. However, it is not sure that the payload will always be passed, for example if the view is not attached so you should perform some more checks.

Anyway, if you pass null it will be performed a full update to the item and you won't have to worry about it.

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