Android 具有多个项类型的ListAdapter引发ClassCastException
我正在为一个活动构建一个应用程序,其中一个功能是留言板。为此,我构建了一个Android 具有多个项类型的ListAdapter引发ClassCastException,android,listview,classcastexception,baseadapter,Android,Listview,Classcastexception,Baseadapter,我正在为一个活动构建一个应用程序,其中一个功能是留言板。为此,我构建了一个列表视图,并用消息加载它 我有两种类型的消息:你发送的消息和另一种发送的消息。布局略有不同,您使用其他XML文件。我尝试了我的代码(如下),如果所有项目都是同一类型(您的或其他项目),那么它可以正常工作。但是当类型发生变化时,我会得到一个ClassCastException。我知道这意味着什么,以及哪里出了问题(ItemHolder属于不同的类,它试图使类的对象不是它的对象),但不知道如何解决它 这是我的代码,这是我的聊天
列表视图
,并用消息加载它
我有两种类型的消息:你发送的消息和另一种发送的消息。布局略有不同,您使用其他XML文件。我尝试了我的代码(如下),如果所有项目都是同一类型(您的或其他项目),那么它可以正常工作。但是当类型发生变化时,我会得到一个ClassCastException
。我知道这意味着什么,以及哪里出了问题(ItemHolder属于不同的类,它试图使类的对象不是它的对象),但不知道如何解决它
这是我的代码,这是我的聊天适配器的getView。
ChatAdapter
是扩展BaseAdapter
的类
public View getView(final int position, View convertView, ViewGroup parent) {
View vi=convertView;
final Message m = messagelist.get(position);
OwnMessageHolder ownMessageHolder;
OtherMessageHolder otherMessageHolder;
if(isSelf(m.getPerson().getId())) {
if (vi == null) { //convertview==null
ownMessageHolder = new OwnMessageHolder();
vi = inflater.inflate(R.layout.listitem_chat_own, null);
vi.setOnClickListener(null);
vi.setOnLongClickListener(null);
vi.setLongClickable(false);
ownMessageHolder.name = (TextView) vi.findViewById(R.id.tv_chat_own_name);
ownMessageHolder.message = (TextView) vi.findViewById(R.id.tv_chat_own_message);
vi.setTag(ownMessageHolder);
}else{//convertview is not null
ownMessageHolder = (OwnMessageHolder)vi.getTag();
}
ownMessageHolder.name.setText(m.getPerson().getName());
ownMessageHolder.message.setText(m.getMessages()[0]);
vi.setFocusable(false);
vi.setClickable(true);
return vi;
}else {//other
if (vi == null) { //convertview==null
otherMessageHolder = new OtherMessageHolder();
vi = inflater.inflate(R.layout.listitem_chat_other, null);
vi.setOnClickListener(null);
vi.setOnLongClickListener(null);
vi.setLongClickable(false);
otherMessageHolder.name = (TextView) vi.findViewById(R.id.tv_chat_other_name);
otherMessageHolder.message = (TextView) vi.findViewById(R.id.tv_chat_other_message);
vi.setTag(otherMessageHolder);
}else{//convertview is not null
otherMessageHolder = (OtherMessageHolder)vi.getTag();
}
otherMessageHolder.name.setText(m.getPerson().getName());
otherMessageHolder.message.setText(m.getMessages()[0]);
vi.setFocusable(false);
vi.setClickable(true);
return vi;
}
}
public static class OwnMessageHolder {
public TextView name;
public TextView message;
}
public static class OtherMessageHolder {
public TextView name;
public TextView message;
}
以及错误日志:
04-06 23:25:54.720: E/AndroidRuntime(18176): FATAL EXCEPTION: main
04-06 23:25:54.720: E/AndroidRuntime(18176): java.lang.ClassCastException: com.hera.lustrumvirgiel.ChatAdapter$OtherMessageHolder cannot be cast to com.hera.lustrumvirgiel.ChatAdapter$OwnMessageHolder
04-06 23:25:54.720: E/AndroidRuntime(18176): at com.hera.lustrumvirgiel.ChatAdapter.getView(ChatAdapter.java:57)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.AbsListView.obtainView(AbsListView.java:2449)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.ListView.measureHeightOfChildren(ListView.java:1244)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.ListView.onMeasure(ListView.java:1155)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.View.measure(View.java:12815)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.RelativeLayout.measureChild(RelativeLayout.java:627)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:440)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.View.measure(View.java:12815)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.View.measure(View.java:12815)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1399)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.LinearLayout.measureVertical(LinearLayout.java:690)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.LinearLayout.onMeasure(LinearLayout.java:583)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.View.measure(View.java:12815)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4698)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
04-06 23:25:54.720: E/AndroidRuntime(18176): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2106)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.View.measure(View.java:12815)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1068)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2452)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.os.Handler.dispatchMessage(Handler.java:99)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.os.Looper.loop(Looper.java:137)
04-06 23:25:54.720: E/AndroidRuntime(18176): at android.app.ActivityThread.main(ActivityThread.java:4493)
04-06 23:25:54.720: E/AndroidRuntime(18176): at java.lang.reflect.Method.invokeNative(Native Method)
04-06 23:25:54.720: E/AndroidRuntime(18176): at java.lang.reflect.Method.invoke(Method.java:511)
04-06 23:25:54.720: E/AndroidRuntime(18176): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:788)
04-06 23:25:54.720: E/AndroidRuntime(18176): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
04-06 23:25:54.720: E/AndroidRuntime(18176): at dalvik.system.NativeStart.main(Native Method)
有人知道如何解决这个问题吗?错误日志引用的行(57)如下所示:
ownMessageHolder=(ownMessageHolder)vi.getTag()
提前谢谢 Java的
instanceof
关键字似乎就是您要寻找的。它允许您确定对象是否是特定类的实例。在强制转换对象之前,在if语句中使用此选项特别方便:
Object tag = vi.getTag();
if (tag instanceof OtherMessageHolder)
otherMessageHolder = (OtherMessageHolder)tag;
else // Assume it is an OwnMessageHolder
ownMessageHolder = (OwnMessageHolder)tag;
Java的
instanceof
关键字似乎就是您要寻找的。它允许您确定对象是否是特定类的实例。在强制转换对象之前,在if语句中使用此选项特别方便:
Object tag = vi.getTag();
if (tag instanceof OtherMessageHolder)
otherMessageHolder = (OtherMessageHolder)tag;
else // Assume it is an OwnMessageHolder
ownMessageHolder = (OwnMessageHolder)tag;
您正在尝试使用多个布局:
vi = inflater.inflate(R.layout.listitem_chat_own, null);
vi = inflater.inflate(R.layout.listitem_chat_other, null);
但是您没有告诉适配器期望不止一个。。。这将导致ListView的RecycleBin出现很多问题,而且效率也不会那么高。只需覆盖并使用
getItemViewType()
内部getView()
加载适当的布局,适配器将处理其余布局。您正在尝试使用多个布局:
vi = inflater.inflate(R.layout.listitem_chat_own, null);
vi = inflater.inflate(R.layout.listitem_chat_other, null);
但是您没有告诉适配器期望不止一个。。。这将导致ListView的RecycleBin出现很多问题,而且效率也不会那么高。只需覆盖,然后使用getItemViewType()
内部getView()
加载适当的布局,适配器将处理其余部分