对base-adapter-helper的简单分析

在微博上看到了这篇Android ListView适配器应该这样写，受益匪浅。
于是依据文章结尾的介绍来到了base-adapter-helper的github，地址：https://github.com/JoanZapata/base-adapter-helper
然后下载看看，我等小菜也来分析分析。
源代码包括4个文件：
BaseAdapterHelper.java
BaseQuickAdapter.java
EnhancedQuickAdapter.java
QuickAdapter.java
其中最基本的是前两个。

先看BaseAdapterHelper。第一个文章也写了，这个类是替代viewHolder的。进一步封装优化的产物，包括一些封装好的经常使用功能，比方imageView图片的载入，文本框改动文本，给控件加入各种事件等等。
先上代码，凝视我自己加的：

package com.joanzapata.android;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.graphics.drawable.Drawable;
import android.os.Build;
import android.text.util.Linkify;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.AlphaAnimation;
import android.widget.*;
import com.squareup.picasso.Picasso;
import com.squareup.picasso.RequestCreator;

public class BaseAdapterHelper {

    private final SparseArray<View> views;//相似hashMap ,可是更高效强大

    private final Context context;

    private int position;

    private View convertView;

    Object associatedObject;//item的数据 item

    protected BaseAdapterHelper(Context context, ViewGroup parent, int layoutId, int position) {
        this.context = context;
        this.position = position;
        this.views = new SparseArray<View>();
        convertView = LayoutInflater.from(context) 
                .inflate(layoutId, parent, false);
        convertView.setTag(this);
    }
    //  静态方法。依据listview里getView的參数生成BaseAdapterHelper
    public static BaseAdapterHelper get(Context context, View convertView, ViewGroup parent, int layoutId) {
        return get(context, convertView, parent, layoutId, -1);
    }

    static BaseAdapterHelper get(Context context, View convertView, ViewGroup parent, int layoutId, int position) {
        if (convertView == null) {
            return new BaseAdapterHelper(context, parent, layoutId, position);
        }
        BaseAdapterHelper existingHelper = (BaseAdapterHelper) convertView.getTag();
        existingHelper.position = position;
        return existingHelper;
    }

    //  依据id得到控件
    public <T extends View> T getView(int viewId) {
        return retrieveView(viewId);
    }

    @SuppressWarnings("unchecked")
    protected <T extends View> T retrieveView(int viewId) {
        View view = views.get(viewId);
        if (view == null) {
            view = convertView.findViewById(viewId);
            views.put(viewId, view);
        }
        return (T) view;
    }

    //  textview 设置文字
    public BaseAdapterHelper setText(int viewId, String value) {
        TextView view = retrieveView(viewId);
        view.setText(value);
        return this;
    }

    //  设置图片
    public BaseAdapterHelper setImageResource(int viewId, int imageResId) {
        ImageView view = retrieveView(viewId);
        view.setImageResource(imageResId);
        return this;
    }

    //  设置颜色
    public BaseAdapterHelper setBackgroundColor(int viewId, int color) {
        View view = retrieveView(viewId);
        view.setBackgroundColor(color);
        return this;
    }

    //  设置背景图片
    public BaseAdapterHelper setBackgroundRes(int viewId, int backgroundRes) {
        View view = retrieveView(viewId);
        view.setBackgroundResource(backgroundRes);
        return this;
    }

    public BaseAdapterHelper setTextColor(int viewId, int textColor) {
        TextView view = retrieveView(viewId);
        view.setTextColor(textColor);
        return this;
    }

    public BaseAdapterHelper setTextColorRes(int viewId, int textColorRes) {
        TextView view = retrieveView(viewId);
        view.setTextColor(context.getResources().getColor(textColorRes));
        return this;
    }

    public BaseAdapterHelper setImageDrawable(int viewId, Drawable drawable) {
        ImageView view = retrieveView(viewId);
        view.setImageDrawable(drawable);
        return this;
    }

    //  设置图片url 。异步下载图片
    public BaseAdapterHelper setImageUrl(int viewId, String imageUrl) {
        ImageView view = retrieveView(viewId);
        Picasso.with(context).load(imageUrl).into(view);
        return this;
    }

    //  requestBuilder是Picasso request builder ，异步载入图片
    public BaseAdapterHelper setImageBuilder(int viewId, RequestCreator requestBuilder) {
        ImageView view = retrieveView(viewId);
        requestBuilder.into(view);
        return this;
    }

    public BaseAdapterHelper setImageBitmap(int viewId, Bitmap bitmap) {
        ImageView view = retrieveView(viewId);
        view.setImageBitmap(bitmap);
        return this;
    }

    //  设置图片的透明度
    public BaseAdapterHelper setAlpha(int viewId, float value) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
            retrieveView(viewId).setAlpha(value);
        } else {
            // Pre-honeycomb hack to set Alpha value
            AlphaAnimation alpha = new AlphaAnimation(value, value);
            alpha.setDuration(0);
            alpha.setFillAfter(true);
            retrieveView(viewId).startAnimation(alpha);
        }
        return this;
    }

    public BaseAdapterHelper setVisible(int viewId, boolean visible) {
        View view = retrieveView(viewId);
        view.setVisibility(visible ?
 View.VISIBLE : View.GONE);
        return this;
    }

    //加入 addLinks
    public BaseAdapterHelper linkify(int viewId) {
        TextView view = retrieveView(viewId);
        Linkify.addLinks(view, Linkify.ALL);
        return this;
    }

    //  文本框字体
    public BaseAdapterHelper setTypeface(int viewId, Typeface typeface) {
        TextView view = retrieveView(viewId);
        view.setTypeface(typeface);
        view.setPaintFlags(view.getPaintFlags() | Paint.SUBPIXEL_TEXT_FLAG);
        return this;
    }

    public BaseAdapterHelper setTypeface(Typeface typeface, int... viewIds) {
        for (int viewId : viewIds) {
            TextView view = retrieveView(viewId);
            view.setTypeface(typeface);
            view.setPaintFlags(view.getPaintFlags() | Paint.SUBPIXEL_TEXT_FLAG);
        }
        return this;
    }

    //  设置进度条
    public BaseAdapterHelper setProgress(int viewId, int progress) {
        ProgressBar view = retrieveView(viewId);
        view.setProgress(progress);
        return this;
    }

    public BaseAdapterHelper setProgress(int viewId, int progress, int max) {
        ProgressBar view = retrieveView(viewId);
        view.setMax(max);
        view.setProgress(progress);
        return this;
    }

    public BaseAdapterHelper setMax(int viewId, int max) {
        ProgressBar view = retrieveView(viewId);
        view.setMax(max);
        return this;
    }

    public BaseAdapterHelper setRating(int viewId, float rating) {
        RatingBar view = retrieveView(viewId);
        view.setRating(rating);
        return this;
    }

    public BaseAdapterHelper setRating(int viewId, float rating, int max) {
        RatingBar view = retrieveView(viewId);
        view.setMax(max);
        view.setRating(rating);
        return this;
    }

    //  设置控件的点击事件
    public BaseAdapterHelper setOnClickListener(int viewId, View.OnClickListener listener) {
        View view = retrieveView(viewId);
        view.setOnClickListener(listener);
        return this;
    }

    //  设置控件的onTouch事件
    public BaseAdapterHelper setOnTouchListener(int viewId, View.OnTouchListener listener) {
        View view = retrieveView(viewId);
        view.setOnTouchListener(listener);
        return this;
    }


    public BaseAdapterHelper setOnLongClickListener(int viewId, View.OnLongClickListener listener) {
        View view = retrieveView(viewId);
        view.setOnLongClickListener(listener);
        return this;
    }

    //  设置控件的tag
    public BaseAdapterHelper setTag(int viewId, Object tag) {
        View view = retrieveView(viewId);
        view.setTag(tag);
        return this;
    }

    public BaseAdapterHelper setTag(int viewId, int key, Object tag) {
        View view = retrieveView(viewId);
        view.setTag(key, tag);
        return this;
    }

    //  设置选中状态
    public BaseAdapterHelper setChecked(int viewId, boolean checked) {
        Checkable view = (Checkable) retrieveView(viewId);
        view.setChecked(checked);
        return this;
    }

    //  设置adapter
    public BaseAdapterHelper setAdapter(int viewId, Adapter adapter) {
        AdapterView view = retrieveView(viewId);
        view.setAdapter(adapter);
        return this;
    }

    public View getView() {
        return convertView;
    }

    //  得到item的position，假设是-1，则异常
    public int getPosition() {
        if (position == -1)
            throw new IllegalStateException("Use BaseAdapterHelper constructor " +
                    "with position if you need to retrieve the position.");
        return position;
    }

    public Object getAssociatedObject() {
        return associatedObject;
    }

    /** Should be called during convert */
    public void setAssociatedObject(Object associatedObject) {
        this.associatedObject = associatedObject;
    }
}

构造函数是一些初始化，convertView的载入。views的初始化。

看这个静态方法，static BaseAdapterHelper get(Context context, View convertView, ViewGroup parent, int layoutId, int position)，能够通过类名.的方式生成这个类的实例。传入的convertView是listview的getView方法里的。layoutId即为item的布局文件id。
protected <T extends View> T retrieveView(int viewId)这种方法替代了holderview的作用。
后面的方法都是设置控件的属性或者事件等等，注意associatedObject这个属性是item的data，所以是Object类型。

再看看核心的BaseQuickAdapter。
代码：

package com.joanzapata.android;

import android.content.Context;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.FrameLayout;
import android.widget.ProgressBar;

import java.util.ArrayList;
import java.util.List;


public abstract class BaseQuickAdapter<T, H extends BaseAdapterHelper> extends BaseAdapter {

    protected static final String TAG = BaseQuickAdapter.class.getSimpleName();

    protected final Context context;

    protected final int layoutResId;

    protected final List<T> data;

    protected boolean displayIndeterminateProgress = false;


    public BaseQuickAdapter(Context context, int layoutResId) {
        this(context, layoutResId, null);
    }

    //依据layoutId和data初始化
    public BaseQuickAdapter(Context context, int layoutResId, List<T> data) {
        this.data = data == null ? new ArrayList<T>() : new ArrayList<T>(data);
        this.context = context;
        this.layoutResId = layoutResId;
    }

    //假设Progress显示则加1
    @Override
    public int getCount() {
        int extra = displayIndeterminateProgress ?
 1 : 0;
        return data.size() + extra;
    }

    @Override
    public T getItem(int position) {
        if (position >= data.size()) return null;
        return data.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    //  item type的数量，两种，一种是item，都是同样的，还有一种是Progress
    @Override
    public int getViewTypeCount() {
        return 2;
    }

    //  当position超过data数量时，载入progress，是还有一种布局
    @Override
    public int getItemViewType(int position) {
        return position >= data.size() ?
 1 : 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (getItemViewType(position) == 0) {//普通布局
            final H helper = getAdapterHelper(position, convertView, parent);//getAdapterHelper()是一个抽象方法，子类实现，须要提供的參数是layoutID，也就是item的布局
            T item = getItem(position);
            helper.setAssociatedObject(item);
            convert(helper, item);//convert须要之类实现。功能逻辑
            return helper.getView();
        }
        return createIndeterminateProgressView(convertView, parent);//载入progress布局
    }

    private View createIndeterminateProgressView(View convertView, ViewGroup parent) {
        if (convertView == null) {
            FrameLayout container = new FrameLayout(context);
            container.setForegroundGravity(Gravity.CENTER);
            ProgressBar progress = new ProgressBar(context);
            container.addView(progress);
            convertView = container;
        }
        return convertView;
    }

    @Override
    public boolean isEnabled(int position) {
        return position < data.size();
    }

    public void add(T elem) {
        data.add(elem);
        notifyDataSetChanged();
    }

    public void addAll(List<T> elem) {
        data.addAll(elem);
        notifyDataSetChanged();
    }

    public void set(T oldElem, T newElem) {
        set(data.indexOf(oldElem), newElem);
    }

    public void set(int index, T elem) {
        data.set(index, elem);
        notifyDataSetChanged();
    }

    public void remove(T elem) {
        data.remove(elem);
        notifyDataSetChanged();
    }

    public void remove(int index) {
        data.remove(index);
        notifyDataSetChanged();
    }

    public void replaceAll(List<T> elem) {
        data.clear();
        data.addAll(elem);
        notifyDataSetChanged();
    }

    public boolean contains(T elem) {
        return data.contains(elem);
    }

    /** Clear data list */
    public void clear() {
        data.clear();
        notifyDataSetChanged();
    }

    public void showIndeterminateProgress(boolean display) {
        if (display == displayIndeterminateProgress) return;
        displayIndeterminateProgress = display;
        notifyDataSetChanged();
    }

    /**
     * Implement this method and use the helper to adapt the view to the given item.
     * @param helper A fully initialized helper.
     * @param item   The item that needs to be displayed.
     */
    protected abstract void convert(H helper, T item);

    /**
     * You can override this method to use a custom BaseAdapterHelper in order to fit your needs
     * @param position    The position of the item within the adapter's data set of the item whose view we want.
     * @param convertView The old view to reuse, if possible. Note: You should check that this view
     *                    is non-null and of an appropriate type before using. If it is not possible to convert
     *                    this view to display the correct data, this method can create a new view.
     *                    Heterogeneous lists can specify their number of view types, so that this View is
     *                    always of the right type (see {@link #getViewTypeCount()} and
     *                    {@link #getItemViewType(int)}).
     * @param parent      The parent that this view will eventually be attached to
     * @return An instance of BaseAdapterHelper
     */
    protected abstract H getAdapterHelper(int position, View convertView, ViewGroup parent);

}

这个类继承了BaseAdapter，是抽象类，抽象方法为protected abstract void convert(H helper, T item);和protected abstract H getAdapterHelper(int position, View convertView, ViewGroup parent);供子类实现，convert是用户须要实现的功能逻辑，getAdapterHelper须要用户提供item的layoutId。

这个类设计的是包括两种布局，一种是用户自己定义的item布局，还有一种是Progress的布局，所以在getCount()返回的是data.size()+1,getViewTypeCount()返回2，区分这两种用getItemViewType()。
看最重要的getView()方法，首先依据getItemViewType()推断类型，为0 就是item布局，通过调用子类的getAdapterHelper()方法得到对应的AdapterHelper进行设置。为1就是Progress。通过new了一个FrameLayout布局实现。在item生成过程中，convert()是最重要的。对于实际的开发，一般用于设置item图片载入、文本框设置文本等等相似逻辑。

大概重要的都说了，代码凝视也有。在上面第一个提到的文章里也说了，这个项目不支持item有多个布局，事实上我们能够改动，那篇文章里也有，详细的就是添加一个布局数组，在getView()方法中加以推断，比方聊天界面，有发送方和接收方。布局是左右相反的，一个是靠左。还有一个靠右，在消息类里肯定有这个属性，是否是自己发送。用这个项目其中来。就是重写getItemViewType()，在getView()中推断和载入。

努力学习和运用开源项目，了解后面的原理和流程，对自己思路和能力都有非常大提高，还要继续学习。

。