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我想顯示從應用程序類中定義的ArrayList ListView。然而，每當我在Logcat中給出沒有原因的滾動時，我最終會遇到NullPointerException異常。Android：列表視圖空指針異常無原因
logcat的輸出：
05-17 11:05:35.365: W/System.err(2173): java.lang.NullPointerException
05-17 11:05:35.375: W/System.err(2173): at in.net.maloo.HomeScreenListView$myAdapter.getView(HomeScreenListView.java:66)
05-17 11:05:35.385: W/System.err(2173): at android.widget.AbsListView.obtainView(AbsListView.java:1294)
05-17 11:05:35.385: W/System.err(2173): at android.widget.ListView.makeAndAddView(ListView.java:1727)
05-17 11:05:35.395: W/System.err(2173): at android.widget.ListView.fillDown(ListView.java:652)
05-17 11:05:35.395: W/System.err(2173): at android.widget.ListView.fillGap(ListView.java:623)
05-17 11:05:35.395: W/System.err(2173): at android.widget.AbsListView.trackMotionScroll(AbsListView.java:2944)
05-17 11:05:35.405: W/System.err(2173): at android.widget.AbsListView$FlingRunnable.run(AbsListView.java:2485)
05-17 11:05:35.405: W/System.err(2173): at android.os.Handler.handleCallback(Handler.java:587)
05-17 11:05:35.405: W/System.err(2173): at android.os.Handler.dispatchMessage(Handler.java:92)
05-17 11:05:35.415: W/System.err(2173): at android.os.Looper.loop(Looper.java:123)
05-17 11:05:35.415: W/System.err(2173): at android.app.ActivityThread.main(ActivityThread.java:4627)
05-17 11:05:35.415: W/System.err(2173): at java.lang.reflect.Method.invokeNative(Native Method)
05-17 11:05:35.425: W/System.err(2173): at java.lang.reflect.Method.invoke(Method.java:521)
05-17 11:05:35.425: W/System.err(2173): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-17 11:05:35.425: W/System.err(2173): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-17 11:05:35.425: W/System.err(2173): at dalvik.system.NativeStart.main(Native Method)
代碼：
package in.net.maloo;
import android.app.ListActivity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
public class HomeScreenListView extends ListActivity {
private static class myAdapter extends BaseAdapter{
private LayoutInflater mInflater;
public myAdapter(Context context){
mInflater = LayoutInflater.from(context);
}
public int getCount() {
// TODO Auto-generated method stub
return myApp.feedLength(0);
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View conertView, ViewGroup parent) {
ViewHolder holder;
if (conertView == null) {
conertView = mInflater.inflate(R.layout.listview_homescreen, null);
holder = new ViewHolder();
holder.text1 = (TextView) conertView.findViewById(R.id.hs_listview_symbol);
holder.text2 = (TextView) conertView.findViewById(R.id.hs_listview_price);
holder.text3 = (TextView) conertView.findViewById(R.id.hs_listview_unit);
holder.text4 = (TextView) conertView.findViewById(R.id.hs_listview_change);
holder.text5 = (TextView) conertView.findViewById(R.id.hs_listview_pcp);
} else {
holder = (ViewHolder) conertView.getTag();
}
String com, ltp, volume, ltq, pcp;
com = myApp.getFuturesData(position, "Commodity", 0) + " - " + myApp.getFuturesData(position, "Expiry", 0);
ltp = myApp.getFuturesData(position, "LTP") + "";
ltq = "LTQ: " + myApp.getFuturesData(position, "LTQ");
volume = "Volume: " + myApp.getFuturesData(position, "Volume");
pcp = "PCP: " + myApp.getFuturesData(position, "PCP");
try {
holder.text1.setText(com);
Log.e("Position", com);
holder.text2.setText(ltp);
holder.text3.setText(volume);
holder.text4.setText(ltq);
holder.text5.setText(pcp);
return conertView;
}
catch (NullPointerException e){
e.printStackTrace();
}
finally {
return conertView;
}
}
static class ViewHolder {
TextView text1;
TextView text2;
TextView text3;
TextView text4;
TextView text5;
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setListAdapter(new myAdapter(this));
}
}
listview_homescreen佈局：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="75dip" >
<TextView
android:id="@+id/hs_listview_symbol"
android:layout_width="200dip"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_alignRight="@+id/hs_listview_change"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textColor="@android:color/tertiary_text_light"
android:textSize="17dip" />
<TextView
android:id="@+id/hs_listview_price"
android:layout_width="75dip"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:text="28,788"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textSize="15dip" />
<TextView
android:id="@+id/hs_listview_unit"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:text="Vol"
android:textAppearance="?android:attr/textAppearanceSmall" />
<TextView
android:id="@+id/hs_listview_pcp"
android:layout_width="75dip"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:text="PCP"
android:textAppearance="?android:attr/textAppearanceSmall" />
<TextView
android:id="@+id/hs_listview_change"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:text="Small Text"
android:textAppearance="?android:attr/textAppearanceSmall" />
</RelativeLayout>
</LinearLayout>
鴨父母，convertView.getTag（）方法返回null由於某種原因，因此所有的問題。當我之前使用對myApp中定義的數組的直接引用時，相同的代碼正常工作，但後來我切換到使用持有不同數據類型的自定義類的ArrayList。
如果重要，ListView活動包含在包含3個選項卡的Tabhost中。
任何與此有關的幫助將不勝感激。謝謝！
歡迎來到SO。如果下面的答案之一解決了您的問題，您應該接受它（點擊相應答案旁邊的複選標記）。這有兩件事。它可以讓每個人都知道你的問題已經得到解決，並且可以幫助你獲得幫助。如果你認爲某些東西真的有用，那麼你也可以加快它的速度（點擊答案旁邊的向上箭頭）。祝你好運！ – Barak
這是一個6歲的問題。如果你是從中世紀的時代投票的話，至少請發表一個理由。 – Puneet