1

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ListView并加载了消息。

我有两种类型的消息：您发送的消息和对方发送的消息。布局略有不同，U 使用其他 XML 文件。我尝试了我的代码（如下），如果所有项目都属于同一类型（您的或其他项目），它工作正常。但是当类型发生变化时，我得到一个ClassCastException. 我知道这意味着什么，以及哪里出了问题（物品持有者属于不同的类，它试图使该类的对象不是），但不知道如何解决它。

这是我的代码，这是我的ChatAdapter. ChatAdapter是一个扩展的类BaseAdapter。

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;
}

和错误日志：

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)

任何人都知道如何解决这个问题？错误日志所指的行 (57) 是这一行：

ownMessageHolder = (OwnMessageHolder)vi.getTag();

提前致谢！

4

2 回答 2

4

您正在尝试使用多种布局：

vi = inflater.inflate(R.layout.listitem_chat_own, null);
vi = inflater.inflate(R.layout.listitem_chat_other, null);

但是您并没有告诉适配器期望超过一个......这将导致 ListView 的 RecycleBin 出现很多问题，并且效率不会那么高。只需覆盖getViewTypeCount()然后getItemViewType()使用getItemViewType()insidegetView()来加载适当的布局，然后适配器将处理其余部分。

于 2013-04-06T22:07:02.040 回答
3

Java 的instanceof关键字似乎正是您要寻找的。它允许您确定对象是否是特定类的实例。这在转换对象之前在 if 语句中使用特别方便：

Object tag = vi.getTag();
if (tag instanceof OtherMessageHolder)
    otherMessageHolder = (OtherMessageHolder)tag;
else // Assume it is an OwnMessageHolder
    ownMessageHolder = (OwnMessageHolder)tag;
于 2013-04-06T21:53:42.673 回答