Android中利用ViewHolder优化自定义Adapter的写法(必看)

最近写Adapter写得多了，慢慢就熟悉了。

用ViewHolder，主要是进行一些性能优化，减少一些不必要的重复操作。（WXD同学教我的。）

具体不分析了，直接上一份代码吧：

public class MarkerItemAdapter extends BaseAdapter
{
  private Context mContext = null;
  private List<MarkerItem> mMarkerData = null;
  public MarkerItemAdapter(Context context, List<MarkerItem> markerItems)
  {
    mContext = context;
    mMarkerData = markerItems;
  }
  public void setMarkerData(List<MarkerItem> markerItems)
  {
    mMarkerData = markerItems;
  }
  @Override
  public int getCount()
  {
    int count = 0;
    if (null != mMarkerData)
    {
      count = mMarkerData.size();
    }
    return count;
  }
  @Override
  public MarkerItem getItem(int position)
  {
    MarkerItem item = null;
    if (null != mMarkerData)
    {
      item = mMarkerData.get(position);
    }
    return item;
  }
  @Override
  public long getItemId(int position)
  {
    return position;
  }
  @Override
  public View getView(int position, View convertView, ViewGroup parent)
  {
    ViewHolder viewHolder = null;
    if (null == convertView)
    {
      viewHolder = new ViewHolder();
      LayoutInflater mInflater = LayoutInflater.from(mContext);
      convertView = mInflater.inflate(R.layout.item_marker_item, null);
      viewHolder.name = (TextView) convertView.findViewById(R.id.name);
      viewHolder.description = (TextView) convertView
          .findViewById(R.id.description);
      viewHolder.createTime = (TextView) convertView
          .findViewById(R.id.createTime);
      convertView.setTag(viewHolder);
    }
    else
    {
      viewHolder = (ViewHolder) convertView.getTag();
    }
    // set item values to the viewHolder:
    MarkerItem markerItem = getItem(position);
    if (null != markerItem)
    {
      viewHolder.name.setText(markerItem.getName());
      viewHolder.description.setText(markerItem.getDescription());
      viewHolder.createTime.setText(markerItem.getCreateDate());
    }
    return convertView;
  }
  private static class ViewHolder
  {
    TextView name;
    TextView description;
    TextView createTime;
  }
}

其中MarkerItem是自定义的类，其中包含name，description，createTime等字段，并且有相应的get和set方法。

ViewHolder是一个内部类，其中包含了单个项目布局中的各个控件。

单个项目的布局，即R.layout.item_marker_item如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:Android="Http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical" 
  android:padding="5dp">
  <TextView
    android:id="@+id/name"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Name"
    android:textSize="20sp"
    android:textStyle="bold" />
  <TextView
    android:id="@+id/description"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Description"
    android:textSize="18sp" />
  <TextView
    android:id="@+id/createTime"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="CreateTime"
    android:textSize="16sp" />
</LinearLayout>

官方的API Demos中也有这个例子：

package com.example.android.apis.view中的List14：

package com.example.android.apis.view;
import android.app.ListActivity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
import android.widget.ImageView;
import android.graphics.BitmapFactory;
import android.graphics.Bitmap;
import com.example.android.apis.R;

public class List14 extends ListActivity {
  private static class EfficientAdapter extends BaseAdapter {
    private LayoutInflater mInflater;
    private Bitmap mIcon1;
    private Bitmap mIcon2;
    public EfficientAdapter(Context context) {
      // Cache the LayoutInflate to avoid asking for a new one each time.
      mInflater = LayoutInflater.from(context);
      // Icons bound to the rows.
      mIcon1 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_1);
      mIcon2 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_2);
    }
    
    public int getCount() {
      return DATA.length;
    }
    
    public Object getItem(int position) {
      return position;
    }
    
    public long getItemId(int position) {
      return position;
    }
    
    public View getView(int position, View convertView, ViewGroup parent) {
      // A ViewHolder keeps references to children views to avoid unneccessary calls
      // to findViewById() on each row.
      ViewHolder holder;
      // When convertView is not null, we can reuse it directly, there is no need
      // to reinflate it. We only inflate a new View when the convertView supplied
      // by ListView is null.
      if (convertView == null) {
        convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
        // Creates a ViewHolder and store references to the two children views
        // we want to bind data to.
        holder = new ViewHolder();
        holder.text = (TextView) convertView.findViewById(R.id.text);
        holder.icon = (ImageView) convertView.findViewById(R.id.icon);
        convertView.setTag(holder);
      } else {
        // Get the ViewHolder back to get fast access to the TextView
        // and the ImageView.
        holder = (ViewHolder) convertView.getTag();
      }
      // Bind the data efficiently with the holder.
      holder.text.setText(DATA[position]);
      holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
      return convertView;
    }
    static class ViewHolder {
      TextView text;
      ImageView icon;
    }
  }
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setListAdapter(new EfficientAdapter(this));
  }
  private static final String[] DATA = Cheeses.sCheeseStrings;
}

其中布局：

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2007 The Android Open Source Project
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at
     http://www.apache.org/licenses/LICENSE-2.0
   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language Governing permissions and
   limitations under the License.
-->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="horizontal"
  android:layout_width="match_parent"
  android:layout_height="match_parent">
  <ImageView android:id="@+id/icon"
    android:layout_width="48dip"
    android:layout_height="48dip" />
  <TextView android:id="@+id/text"
    android:layout_gravity="center_vertical"
    android:layout_width="0dip"
    android:layout_weight="1.0"
    android:layout_height="wrap_content" />
</LinearLayout>

以上这篇Android中利用ViewHolder优化自定义Adapter的写法(必看)就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持编程网。

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