如果您对ViewHolder模式在自定义CursorAdapter中正确实现了吗？和viewholder感兴趣，那么这篇文章一定是您不可错过的。我们将详细讲解ViewHolder模式在自定义Curso
如果您对ViewHolder模式在自定义CursorAdapter中正确实现了吗？和view holder感兴趣，那么这篇文章一定是您不可错过的。我们将详细讲解ViewHolder模式在自定义CursorAdapter中正确实现了吗？的各种细节，并对view holder进行深入的分析，此外还有关于Android RecyclerView.Adapter onCreateViewHolder()工作、android – ListView with ArrayAdapter和ViewHolder将图标添加到错误的项目、android – Listview和CustomAdapter扩展SimpleCursorAdapter、android – ORMLite性能：ArrayAdapter vs CursorAdapter vs自定义适配器的实用技巧。
本文目录一览：- ViewHolder模式在自定义CursorAdapter中正确实现了吗？（view holder）
- Android RecyclerView.Adapter onCreateViewHolder()工作
- android – ListView with ArrayAdapter和ViewHolder将图标添加到错误的项目
- android – Listview和CustomAdapter扩展SimpleCursorAdapter
- android – ORMLite性能：ArrayAdapter vs CursorAdapter vs自定义适配器
ViewHolder模式在自定义CursorAdapter中正确实现了吗？（view holder）
这是我的自定义CursorAdapter：
public class TasksAdapter extends CursorAdapter implements Filterable { private final Context context; public TasksAdapter(Context context, Cursor c) { super(context, c); this.context = context; } /** * @see android.widget.CursorAdapter#newView(android.content.Context, android.database.Cursor, android.view.ViewGroup) */ @Override public View newView(Context context, Cursor cursor, ViewGroup parent) { LayoutInflater inflater = LayoutInflater.from(context); View v = inflater.inflate(android.R.layout.simple_list_item_checked, parent, false); ViewHolder holder = new ViewHolder(); holder.textview = (CheckedTextView)v.findViewById(android.R.id.text1); v.setTag(holder); return v; } /** * @see android.widget.CursorAdapter#bindView(android.view.View, android.content.Context, android.database.Cursor) */ @Override public void bindView(View view, Context context, Cursor cursor) { ViewHolder holder = (ViewHolder)view.getTag(); int titleCol = cursor.getColumnIndexOrThrow(Tasks.TITLE); int completedCol = cursor.getColumnIndexOrThrow(Tasks.COMPLETED); String title = cursor.getString(titleCol); boolean completed = Util.intToBool(cursor.getInt(completedCol)); holder.textview.setText(title); holder.textview.setChecked(completed); } /** * @see android.widget.CursorAdapter#runQueryOnBackgroundThread(java.lang.CharSequence) */ @Override public Cursor runQueryOnBackgroundThread(CharSequence constraint) { StringBuffer buffer = null; String[] args = null; if (constraint != null) { buffer = new StringBuffer(); buffer.append("UPPER ("); buffer.append(Tasks.TITLE); buffer.append(") GLOB ?"); args = new String[] { "*" + constraint.toString().toUpperCase() + "*" }; } Cursor c = context.getContentResolver().query(Tasks.CONTENT_URI, null, (buffer == null ? null : buffer.toString()), args, Tasks.DEFAULT_SORT_ORDER); c.moveToFirst(); return c; } /** * @see android.widget.CursorAdapter#convertToString(android.database.Cursor) */ @Override public CharSequence convertToString(Cursor cursor) { final int titleCol = cursor.getColumnIndexOrThrow(Tasks.TITLE); String title = cursor.getString(titleCol); return title; } static class ViewHolder { CheckedTextView textview; }}这是否属于ViewHolder模式的约束？我不确定，因为这是CursorAdapter，那里没有getView。如果有任何问题或建议，请指出。
答案1
小编典典CursorAdapter``newView每次需要新行时都不会调用；如果它已经有一个View，它将调用bindView，因此创建的视图实际上已被重用。
就是说，正如 约瑟夫 在评论中指出的那样，您仍然可以使用ViewHolder以避免findViewById重复调用。
如果您仍然担心效率，那么请看一下SimpleCursorAdapter使用的实现WeakHashMap（的映射WeakReferences）：
WeakHashMap<View, View[]> mHolders = new WeakHashMap<View, View[]>();
Android RecyclerView.Adapter onCreateViewHolder()工作
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup,int viewType) {
if(viewType==TYPE_ITEM) {
View mView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.inflate_common_item,viewGroup,false);
ViewHolder vh = new ViewHolder(mView);
return vh;
} else {
View mView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.inflate_uncommon_item,false);
ViewHolderFooter vh = new ViewHolderFooter(mView);
return vh;
}
}
所以我在我的列表中有10个项目,所以每个项目这个方法将被调用,并且每当一个新的ViewHolder将被创建当然,它将有一次为每个视图,但现在我的问题是当我们使用ListView和BaseAdapter与我们将ViewHolder存储在标签中并使用它.我们不会为每个项目创建ViewHolder.
@Override
public View getView(int position,View convertView,ViewGroup parent) {
MyViewHolder mViewHolder;
if(convertView == null) {
convertView = inflater.inflate(R.layout.layout_list_item,null);
mViewHolder = new MyViewHolder();
convertView.setTag(mViewHolder);
} else {
mViewHolder = (MyViewHolder) convertView.getTag();
}
mViewHolder.tvTitle = detail(convertView,R.id.tvTitle,myList.get(position).getTitle());
mViewHolder.tvDesc = detail(convertView,R.id.tvDesc,myList.get(position).getDescription());
mViewHolder.ivIcon = detail(convertView,R.id.ivIcon,myList.get(position).getImgResId());
return convertView;
}
所以我们不会创建额外的观看者对象.请帮我理解利弊.
谢谢
解决方法
它类似于ListView中的代码(检查convertView是否为null,如果没有,请从标签中抓取现有的ViewHolder),但使用RecyclerView,这一切都将自动完成.
我想这是使用RecyclerView的专业人士之一 – 您不必担心像ViewView那样重用ViewHolders. con Rec RecyclerView是非常可定制的,但内置功能很少 – 与ListView不同,它不是很可定制的,但内置了很多功能.
android – ListView with ArrayAdapter和ViewHolder将图标添加到错误的项目
通常一切都很好(名称正确地添加到列表中,与图标一起).但是显示性别的图标会被添加到ListView中的错误项目中.名称将添加到列表的底部,但图标将放置在列表顶部的名称处.我不知道这是否是我使用ViewHolder的方式,但在Android website中没有文档.
// Listview inflater
inflater = (LayoutInflater) (this).getSystemService(LAYOUT_INFLATER_SERVICE);
// List Array.
mAdapter = new ArrayAdapter<String>(this,R.layout.player_simple_list,R.id.label,mStrings) {
@Override
public View getView(int position,View convertView,ViewGroup parent) {
Log.i("ANDY","View getView Called");
// A ViewHolder keeps references to children views to
// avoid unneccessary calls to findViewById() on each row.
ViewHolder holder;
if (null == convertView) {
Log.i("ANDY","Position not prevIoUsly used,so inflating");
convertView = inflater.inflate(R.layout.player_simple_list,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.label);
holder.icon = (ImageView) convertView.findViewById(R.id.icon);
if (sexmale == true) {
holder.icon.setimageBitmap(maleicon);
}
else {
holder.icon.setimageBitmap(femaleicon);
}
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(getItem(position));
// Change icon depending is the sexmale variable is true or false.
Log.i("ANDY","getCount = "+mAdapter.getCount());
return convertView;
}
};
setlistadapter(mAdapter);
解决方法
public View getView(int position,ViewGroup parent) {
Log.i("ANDY","View getView Called");
// A ViewHolder keeps references to children views
// to avoid unneccessary calls to findViewById() on each row.
ViewHolder holder;
if (null == convertView) {
Log.i("ANDY",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.label);
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(getItem(position));
// Change icon depending is the sexmale variable is true or false.
if (sexmale == true) {
holder.icon.setimageBitmap(maleicon);
}
else {
holder.icon.setimageBitmap(femaleicon);
}
Log.i("ANDY","getCount = "+mAdapter.getCount());
return convertView;
}
android – Listview和CustomAdapter扩展SimpleCursorAdapter
我希望操纵ListView中所选行的背景颜色,从阅读中我需要使用CustomAdapter进行扩展.我的主适配器是SimpleCursorAdapter类型,所以我修改了一个将ArrayAdapter扩展为SimpleCursorAdapter的CustomAdapter.
我的问题是使用CustomAdapter时listview是空白但如果不扩展并使用SimpleCursorAdapter,listview有行/项.
Logcat在我的CustomAdapter中显示一个问题,见下文.
这是我的主要活动代码：
phrasesdb helper = new phrasesdb(this);
database = helper.getWritableDatabase();
data = database.query("phrases",fields,null,fields[0] + " COLLATE NOCASE ASC");
//WORKING SimpleCursorAdapter
//dataSource = new SimpleCursorAdapter(this,R.layout.phrases,data,new int[] { R.id.phrase });
//NOT WORKING
dataSource = new CustomAdapter(this,new int[] { R.id.phrase });
view = getListView();
setlistadapter(dataSource);
这是Custom Adapter类,我已经标记了logcat错误的位置：
import android.content.Context;
import android.database.Cursor;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.SimpleCursorAdapter;
import android.widget.TextView;
public class CustomAdapter extends SimpleCursorAdapter {
protected static final int NO_SELECTED_COLOR = 0xFF191919;
protected static final int SELECTED_COLOR = 0xFF3366CC;
Cursor items;
private LayoutInflater mInflater;
private int viewResourceId;
private int selectedPosition;
public CustomAdapter(Context context,int resourceId,Cursor data,String[] fields,int[] is) {
super(context,resourceId,is);
mInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
viewResourceId = resourceId;
items = data;
}
@Override
public View getView(int position,View convertView,ViewGroup parent) {
TextView tv = (TextView)convertView;
if (tv == null) {
//WHEN DEBUGGING THIS IS WHERE LOGCAT ERROR MESSAGES STARTS
tv = (TextView)mInflater.inflate(viewResourceId,null);
}
tv.setText(items.getString(position));
// Change the background color
if (position==selectedPosition) tv.setBackgroundColor(SELECTED_COLOR);
else tv.setBackgroundColor(NO_SELECTED_COLOR);
return tv;
}
public void setSelected(int position) {
selectedPosition = position;
}
}
这是LogCat：
10-18 13:33:17.869: E/ListView(28378): android.widget.LinearLayout
10-18 13:33:17.869: E/ListView(28378): java.lang.classCastException: android.widget.LinearLayout
10-18 13:33:17.869: E/ListView(28378): at com.xxx.xxx.CustomAdapter.getView(CustomAdapter.java:49)
10-18 13:33:17.869: E/ListView(28378): at android.widget.AbsListView.obtainView(AbsListView.java:1449)
10-18 13:33:17.869: E/ListView(28378): at android.widget.ListView.makeAndAddView(ListView.java:1801)
10-18 13:33:17.869: E/ListView(28378): at android.widget.ListView.fillSpecific(ListView.java:1339)
10-18 13:33:17.869: E/ListView(28378): at android.widget.ListView.layoutChildren(ListView.java:1637)
10-18 13:33:17.869: E/ListView(28378): at android.widget.AbsListView.onLayout(AbsListView.java:1279)
10-18 13:33:17.869: E/ListView(28378): at android.view.View.layout(View.java:7321)
10-18 13:33:17.869: E/ListView(28378): at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
10-18 13:33:17.869: E/ListView(28378): at android.view.View.layout(View.java:7321)
10-18 13:33:17.869: E/ListView(28378): at android.widget.FrameLayout.onLayout(FrameLayout.java:338)
10-18 13:33:17.869: E/ListView(28378): at android.view.View.layout(View.java:7321)
10-18 13:33:17.869: E/ListView(28378): at android.view.ViewRoot.performTraversals(ViewRoot.java:1217)
10-18 13:33:17.869: E/ListView(28378): at android.view.ViewRoot.handleMessage(ViewRoot.java:1991)
10-18 13:33:17.869: E/ListView(28378): at android.os.Handler.dispatchMessage(Handler.java:99)
10-18 13:33:17.869: E/ListView(28378): at android.os.Looper.loop(Looper.java:150)
10-18 13:33:17.869: E/ListView(28378): at android.app.ActivityThread.main(ActivityThread.java:4385)
10-18 13:33:17.869: E/ListView(28378): at java.lang.reflect.Method.invokeNative(Native Method)
10-18 13:33:17.869: E/ListView(28378): at java.lang.reflect.Method.invoke(Method.java:507)
10-18 13:33:17.869: E/ListView(28378): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
10-18 13:33:17.869: E/ListView(28378): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
10-18 13:33:17.869: E/ListView(28378): at dalvik.system.NativeStart.main(Native Method)
这是布局
android – ORMLite性能：ArrayAdapter vs CursorAdapter vs自定义适配器
我有相对较小的H2数据库.我期待不超过100个参赛作品,甚至感觉高居榜首.我有一个列表视图与一些控件,并使用ArrayAdapter调用QueryAll()来填充数据.它完美地工作,因为我可以在按下按钮时修改内存中数组中的数据,然后将结果写入DB而无需重新加载它.但最初的负荷却出乎意料地缓慢
我想知道是否应该使用CursorAdapter,因为它似乎更适合问题或编写自定义适配器来使用DAO Iterator.
使用Cursor或自定义适配器会有性能提升吗？在我看来,感觉就像定制适配器应该提供最佳性能.
解决方法
最好使用自定义适配器
Content provider.今天关于ViewHolder模式在自定义CursorAdapter中正确实现了吗？和view holder的分享就到这里，希望大家有所收获，若想了解更多关于Android RecyclerView.Adapter onCreateViewHolder()工作、android – ListView with ArrayAdapter和ViewHolder将图标添加到错误的项目、android – Listview和CustomAdapter扩展SimpleCursorAdapter、android – ORMLite性能：ArrayAdapter vs CursorAdapter vs自定义适配器等相关知识，可以在本站进行查询。
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