[分享]一种无需设置ViewHolder的ListView写法

[licheedev]

http://www.bignerdranch.com/blog/customizing-android-listview-rows-subclassing/

[licheedev]

顺便转到博客上面了
http://www.licheetec.com/2015/03/21/no-viewholder-listview/

[jinsen47]

已收藏~

[liujingyuan1]

实现下！看看！

[midiao]

我按照http://www.bignerdranch.com/blog/customizing-android-listview-rows-subclassing/
这个博客上自己实现了一遍，结果报错，错误提示出错的是以下这行
ItemView itemView = (ItemView) LayoutInflater.from(parent.getContext()).inflate(R.layout.item_view, parent, false);

Logcat：
android.view.InflateException: Binary XML file line #1: Error inflating class com.jikexueyuan.noviewholder.ItemView
at android.view.LayoutInflater.createView(LayoutInflater.java:603)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:696)
at android.view.LayoutInflater.inflate(LayoutInflater.java:469)
at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
at com.jikexueyuan.noviewholder.ItemView.inflate(ItemView.java:20)
at com.jikexueyuan.noviewholder.ItemAdapter.getView(ItemAdapter.java:22)
at android.widget.AbsListView.obtainView(AbsListView.java:2255)
at android.widget.ListView.makeAndAddView(ListView.java:1790)
at android.widget.ListView.fillDown(ListView.java:691)
at android.widget.ListView.fillFromTop(ListView.java:752)
at android.widget.ListView.layoutChildren(ListView.java:1630)
at android.widget.AbsListView.onLayout(AbsListView.java:2087)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
at android.view.View.layout(View.java:14817)
at android.view.ViewGroup.layout(ViewGroup.java:4631)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1983)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1740)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5600)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
at android.view.Choreographer.doCallbacks(Choreographer.java:574)
at android.view.Choreographer.doFrame(Choreographer.java:544)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
at android.os.Handler.handleCallback(Handler.java:733)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NoSuchMethodException: [class android.content.Context, interface android.util.AttributeSet]
at java.lang.Class.getConstructorOrMethod(Class.java:472)
at java.lang.Class.getConstructor(Class.java:446)
at android.view.LayoutInflater.createView(LayoutInflater.java:568)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:696)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:469)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
            at com.jikexueyuan.noviewholder.ItemView.inflate(ItemView.java:20)
            at com.jikexueyuan.noviewholder.ItemAdapter.getView(ItemAdapter.java:22)
            at android.widget.AbsListView.obtainView(AbsListView.java:2255)
            at android.widget.ListView.makeAndAddView(ListView.java:1790)
            at android.widget.ListView.fillDown(ListView.java:691)
            at android.widget.ListView.fillFromTop(ListView.java:752)
            at android.widget.ListView.layoutChildren(ListView.java:1630)
            at android.widget.AbsListView.onLayout(AbsListView.java:2087)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1055)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
            at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
            at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453)
            at android.widget.FrameLayout.onLayout(FrameLayout.java:388)
            at android.view.View.layout(View.java:14817)
            at android.view.ViewGroup.layout(ViewGroup.java:4631)
            at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1983)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1740)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:996)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5600)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
            at android.view.Choreographer.doCallbacks(Choreographer.java:574)
            at android.view.Choreographer.doFrame(Choreographer.java:544)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5001)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)

@licheetec 能不能抽空看一下，因为实在太疑惑了。

[licheedev]

@midiao 把你的代码发下。

[midiao]

Item.java

public class Item {
private int mImageId;
private String mTitle;
private String mDescription;
public int getmImageId() {
    return mImageId;
}
public void setmImageId(int mImageId) {
    this.mImageId = mImageId;
}
public String getmTitle() {
    return mTitle;
}
public void setmTitle(String mTitle) {
    this.mTitle = mTitle;
}
public String getmDescription() {
    return mDescription;
}
public void setmDescription(String mDescription) {
    this.mDescription = mDescription;
}
}

ItemAdapter.java

public class ItemAdapter extends ArrayAdapter<Item>{
public ItemAdapter(Context c, List<Item> items){
    super(c, 0, items);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    ItemView itemView = (ItemView)convertView;
    if (itemView == null)
        itemView = ItemView.inflate(parent);
    itemView.setItem(getItem(position));
    return itemView;
}
}

ItemView.java

public class ItemView extends RelativeLayout {
private TextView mTitleTextView;
private TextView mDescriptionTextView;
private ImageView mImageView;

public static ItemView inflate(ViewGroup parent) {
    ItemView itemView = (ItemView) LayoutInflater.from(parent.getContext()).inflate(R.layout.item_view, parent, false);
    return itemView;
}

public ItemView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    LayoutInflater.from(context).inflate(R.layout.item_view_children, this, true);
    setupChildren();
}

private void setupChildren() {
    mTitleTextView = (TextView) findViewById(R.id.item_titleTextView);
    mDescriptionTextView = (TextView) findViewById(R.id.item_descriptionTextView);
    mImageView = (ImageView) findViewById(R.id.item_imageView);
}

public void setItem(Item item) {
    mTitleTextView.setText(item.getmTitle());
    mDescriptionTextView.setText(item.getmDescription());
    mImageView.setImageResource(item.getmImageId());
}
}

MainActivity.java

public class MainActivity extends ActionBarActivity {
private ListView listView;
private List<Item> itemList;
private ItemAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    init();
}

private void init(){
    listView = (ListView) findViewById(R.id.listView);
    initData();
    adapter = new ItemAdapter(this, itemList);
    listView.setAdapter(adapter);

}
private void initData(){
    itemList = new ArrayList<>();
    for (int i = 0; i < 100; i++){
        Item item = new Item();
        item.setmImageId(i % 2 == 0 ? R.drawable.img_cat : R.drawable.img_doge);
        item.setmTitle("Title No." + i);
        item.setmDescription("The content of No." + i);
        itemList.add(item);
    }
}
}

activity_main.xml

<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=".MainActivity">

<ListView
    android:id="@+id/listView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"></ListView>
</RelativeLayout>

item.view.xml

<com.jikexueyuan.noviewholder.ItemView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="5dp">
</com.jikexueyuan.noviewholder.ItemView>

item.view.children.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content">

<ImageView
    android:id="@+id/item_imageView"
    android:layout_width="60dp"
    android:layout_height="60dp"
    android:layout_margin="5dp"
    android:background="@android:color/darker_gray"
    android:contentDescription="啦啦啦" />

<TextView
    android:id="@+id/item_titleTextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_toRightOf="@id/item_imageView"
    android:text="title text" />

<TextView
    android:id="@+id/item_descriptionTextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/item_titleTextView"
    android:layout_marginTop="5dp"
    android:layout_toRightOf="@id/item_imageView"
    android:text="description text" />
</merge>

@licheetec

[licheedev]

@midiao 看最后一个有原因的异常信息（Caused by的那个）

Caused by: java.lang.NoSuchMethodException: [class android.content.Context, interface android.util.AttributeSet]

应该是填充xml初始化ItemView的时候，调用的是参数为(Context context, AttributeSet attrs)的构造方法，而你只声明了参数为(Context context, AttributeSet attrs, int defStyle)的这个，改成

    public ItemView(Context context, AttributeSet attrs) {
        super(context, attrs);
        LayoutInflater.from(context).inflate(R.layout.item_view_children, this,
                true);
        setupChildren();
    }

应该就可以了

[midiao]

按你说的修改之后，确实可以了，不过想问问

public ItemView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);  
    LayoutInflater.from(context).inflate(R.layout.item_view_children, this, true);
    setupChildren();
}
public ItemView(Context context, AttributeSet attrs) {
    super(context, attrs);
    LayoutInflater.from(context).inflate(R.layout.item_view_children, this, true);
    setupChildren();
}

这两种构造方法有什么区别呢？（有三个参数的那个构造方法被我注释掉之后，程序依然可以运行；但是如果把两个参数的那个构造方法注释掉程序就会报错），这是为什么呢？
@licheetec

[licheedev]

@midiao 这篇文章有详细说明。

http://www.cnblogs.com/angeldevil/p/3479431.html

[midiao]

受教了，非常感谢指导。
@licheetec

[jorry]

这种实现的原理是什么？

[licheedev]

@jorry 原理其实很简单，就是通过自定义View的方式，把ViewHolder的职能转移到该自定义View上，直接可以在自定义View中缓存子View的引用，而不用经过ViewHolder做中间人。

[liuchenx]

这个写法相当与把setTag的缓存 放到itemview 内存进行全局存储, 我不觉得这个效率比settag高 不过
至于原文作者不喜欢的几个原因, 可以这么写, 也是一个老外写的, 原文找不到了, 用的稀疏数组

public class ViewHolder {
    public static  T get(View view, int id) {
        SparseArray viewHolder = (SparseArray) view.getTag();
        if (viewHolder == null) {
            viewHolder = new SparseArray();
            view.setTag(viewHolder);
        }
        View childView = viewHolder.get(id);
        if (childView == null) {
            childView = view.findViewById(id);
            viewHolder.put(id, childView);
        }
        return (T) childView;
    }
}

上面这个是工具类
下面是getView代码

public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        convertView = mInflater.inflate(R.layout.adapter_listactivity_base_test, null);
    }

    ImageView iv = ViewHolder.get(convertView, R.id.image);
    TextView tv = ViewHolder.get(convertView, R.id.text);

    // to do ...
    // iv.setImageBitmap();
        //  tv.setText();
    return convertView;
}

效率没有实测, 应该差不多, 取决与稀疏数组的查找

[GcsSloop]

看这里，万能适配器：http://www.imooc.com/learn/372