Question

根据有关medthod notifyItemChanged(int position, Object payload)

的RecyclerView文档

通知任何已注册的观察员，该位置的项目已更改为可选的有效负载对象。

我不明白如何在此方法中使用第二个参数payload。我搜索过很多关于＆＃34;有效载荷＆＃34;的文件。但是一切都很暧昧。

所以，如果你知道这个方法，请给我一个明确的例子。非常感谢你。

Answer 1

如果您想更新并非所有持有人视图，只是部分，则可以使用此方法。

您在 ViewHolder

之后的图片

public class ViewHolder extends RecyclerView.ViewHolder {
        public final TextView tvPlayer;
        public final TextView tvScore;

        public ViewHolder(View view) {
            super(view);
            tvPlayer = (TextView) view.findViewById(R.id.tv_player);
            tvScore = (TextView) view.findViewById(R.id.tv_score);
        }

    }

在代码中的某处，您调用适配器来更新单 TextView - tvScore

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

[...]

onBindViewHolder（ViewHolder holder，int position，List payloads） 首先捕获回调。如果payloads与您的要求不符，则必须致电超级super.onBindViewHolder(holder,position, payloads);，其他情况会触发onBindViewHolder(ViewHolder holder, int position)。

     // 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<Object> payloads) {
            if(!payloads.isEmpty()) {
                if (payloads.get(0) instanceof Integer) {
                    holder.tvScore.setText(String.valueOf((Integer)payloads.get(0)))
                }
            }else {
                super.onBindViewHolder(holder,position, payloads);
            }
        }

    // Update ALL VIEW holder
    @Override
        public void onBindViewHolder(ViewHolder holder, int position) {
            MItem item = mList.get(position)
            // some update
        }

Answer 2

查看演示该功能的示例代码。当点击位置RecyclerView的项目时，notifyItemChanged(position, payload)会调用position。您可以通过查找logcat语句来验证是否已调用onBindViewHolder(holder, position, payload)。

确保至少使用支持库的23.1.1版本，如下所示：

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<HelloAdapter.HelloViewHolder> {

        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<Object> payload) {
            Log.d("butt", "payload " + payload.toString());
            bind(holder);
        }

        @Override
        public int getItemCount() {
            return 20;
        }

        private void bind(final HelloViewHolder holder) {
            holder.textView.setText("item " + holder.getAdapterPosition());
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    final int position = holder.getAdapterPosition();
                    Log.d("butt", "click " + position);
                    HelloAdapter.this.notifyItemChanged(position, "payload " + position);
                }
            });
        }

    }

}

activity_main.xml中

<RelativeLayout
    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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".HelloActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>

card_item.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="100dip"
    android:layout_margin="5dip"
    card_view:cardElevation="5dip">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</android.support.v7.widget.CardView>

Answer 3

基本上，将有效载荷视为常数会更方便如果数据集中的数据已经更改，则不必传递任何数据因此，创建几个常量：

public static final String PAYLOAD_NAME = "PAYLOAD_NAME";
public static final String PAYLOAD_AGE = "PAYLOAD_AGE";

然后在适配器中，除了您更新整个项目的常规onBindViewHolder(YourViweHolder holder, int position)之外，例如：

@Override
public void onBindViewHolder(final YourViewHolder holder, final int position) {
    final YourItem item = getItem(position);
    holder.tvName.setText(item.getName());
    holder.tvAge.setText(String.valueOf(item.getAge()));
}

您还实施：

@Override
public void onBindViewHolder(final YourViewHolder holder, final int position, final List<Object> payloads) {
    if (!payloads.isEmpty()) {
        final YourItem item = getItem(position);
        for (final Object payload : payloads) {
            if (payload.equals(PAYLOAD_NAME)) {
               // in this case only name will be updated
               holder.tvName.setText(item.getName());
            } else if (payload.equals(PAYLOAD_AGE)) {
               // only age will be updated
               holder.tvAge.setText(String.valueOf(item.getAge()));
            }
        }
    } else {
        // in this case regular onBindViewHolder will be called
        super.onBindViewHolder(holder, position, payloads);
    }
}

您可以根据需要处理尽可能多的案例，并仅更新实际更改的视图最后一步 - 您只需：

adapter.notifyItemChanged(somePosition, YourAdapter.PAYLOAD_NAME);

Answer 4

您可以传入＆＃34;可选的有效负载对象＆＃34;当您只想在调用ViewHolder方法时对onBindViewHolder中的数据进行部分更新时。但是，它不确定是否总是传递有效负载，例如，如果未附加视图，那么您应该执行更多检查。

无论如何，如果你通过null，它将对该项目进行全面更新，你不必担心它。

需要一个关于RecyclerView.Adapter.notifyItemChanged（int position，Object payload）的示例

4 个答案: