Java Android调用数组列表会导致程序崩溃
我写了一些代码,在一个类中我创建并填充了一个数组列表,我可以从另一个类调用并打印出来,但是当我尝试从第三个类调用它时,会导致移动应用程序关闭。以下是数组列表的代码:Java Android调用数组列表会导致程序崩溃,java,android,mobile,arraylist,Java,Android,Mobile,Arraylist,我写了一些代码,在一个类中我创建并填充了一个数组列表,我可以从另一个类调用并打印出来,但是当我尝试从第三个类调用它时,会导致移动应用程序关闭。以下是数组列表的代码: public class MyPositionOverlay extends ItemizedOverlay<OverlayItem> { public ArrayList<OverlayItem> overlayItemList = new ArrayList<OverlayItem>
public class MyPositionOverlay extends ItemizedOverlay<OverlayItem> {
public ArrayList<OverlayItem> overlayItemList = new ArrayList<OverlayItem>();
Context context;
public MyPositionOverlay(Drawable marker, Context c) {
super(boundCenterBottom(marker));
// TODO Auto-generated constructor stub
populate();
context = c;
}
private final int mRadius = 5;
Location location;
public Location getLocation() {
return location;
}
public void setLocation(Location location) {;
this.location = location;
}
//Method for user intputs - fill in
@Override
public boolean onTap(GeoPoint point, MapView mapView) {
if(super.onTap(point, mapView)){
return true;
}
String title = "Point:" + String.valueOf(overlayItemList.size()+ 1) + "\n" +
"Lat:" + "\n" + String.valueOf(point.getLatitudeE6() +
"Long:" + "\n" + String.valueOf(point.getLongitudeE6()));
String snippet = "geo:\n"
+ String.valueOf(point.getLatitudeE6()) + "\n"
+ String.valueOf(point.getLongitudeE6());
addItem(point, title, snippet);
//return true;
//if(hit test is true)
// perform task
// return true;
//if not handled
return false;
}
@Override
protected boolean onTap(int index) {
// TODO Auto-generated method stub
//return super.onTap(index);
Toast.makeText(context,
"Touch on marker: \n" + overlayItemList.get(index).getTitle(),
Toast.LENGTH_LONG).show();
return true;
}
public void addItem(GeoPoint point, String title, String snippet){
OverlayItem newItem = new OverlayItem(point, title, snippet);
overlayItemList.add(newItem);
populate();
}
@Override
protected OverlayItem createItem(int i) {
// TODO Auto-generated method stub
return overlayItemList.get(i);
}
@Override
public int size() {
// TODO Auto-generated method stub
return overlayItemList.size();
}
}
以下是我收到的错误消息:
06-06 17:14:05.210: W/dalvikvm(1301): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
06-06 17:14:05.220: E/AndroidRuntime(1301): FATAL EXCEPTION: main
06-06 17:14:05.220: E/AndroidRuntime(1301): java.lang.NullPointerException
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.Maps.GeneticAlgorithm2.start(GeneticAlgorithm2.java:97)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.Maps.HomeScreen$3.onClick(HomeScreen.java:152)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.view.View.performClick(View.java:2408)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.view.View$PerformClick.run(View.java:8816)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.os.Handler.handleCallback(Handler.java:587)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.os.Handler.dispatchMessage(Handler.java:92)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.os.Looper.loop(Looper.java:123)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.app.ActivityThread.main(ActivityThread.java:4627)
06-06 17:14:05.220: E/AndroidRuntime(1301): at java.lang.reflect.Method.invokeNative(Native Method)
06-06 17:14:05.220: E/AndroidRuntime(1301): at java.lang.reflect.Method.invoke(Method.java:521)
06-06 17:14:05.220: E/AndroidRuntime(1301): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
06-06 17:14:05.220: E/AndroidRuntime(1301): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
06-06 17:14:05.220: E/AndroidRuntime(1301): at dalvik.system.NativeStart.main(Native Method)
从我所看到的情况来看,数组列表是空的,但正如我所说的,我可以很高兴地从另一个类输出它
请帮助。在您的
开始
方法中位置覆盖
为空,您刚刚声明了它,但在访问此字段之前尚未初始化它,因此NPE。在您的开始
方法中位置覆盖
为空,您刚刚声明了它,但在访问此字段之前尚未初始化它,因此NPE。如果不理解您的用例,这是一个很难回答的问题,无论如何,请看一看这个,好的,但在我看来是应该工作。我有在顶部我的位置覆盖;它将我链接到数组列表所在的类,然后在start方法中我有int populationSize3=positionOverlay.size()。我在另一个班上使用了相同的过程,并且在你的另一个班上进行了精细检查。你在做这样的事情吗。positionOverlay=somePositionOverlay?或者positionOverlay=new MyPositionOverlay()?如果不理解您的用例,这是一个很难回答的问题,不管怎样,请看一看这个问题,好吧,但在我的头脑中是应该工作。我有在顶部我的位置覆盖;它将我链接到数组列表所在的类,然后在start方法中我有int populationSize3=positionOverlay.size()。我在另一个班上使用了相同的过程,并且在你的另一个班上进行了精细检查。你在做这样的事情吗。positionOverlay=somePositionOverlay?或者positionOverlay=new MyPositionOverlay()?
06-06 17:14:05.210: W/dalvikvm(1301): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
06-06 17:14:05.220: E/AndroidRuntime(1301): FATAL EXCEPTION: main
06-06 17:14:05.220: E/AndroidRuntime(1301): java.lang.NullPointerException
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.Maps.GeneticAlgorithm2.start(GeneticAlgorithm2.java:97)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.Maps.HomeScreen$3.onClick(HomeScreen.java:152)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.view.View.performClick(View.java:2408)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.view.View$PerformClick.run(View.java:8816)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.os.Handler.handleCallback(Handler.java:587)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.os.Handler.dispatchMessage(Handler.java:92)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.os.Looper.loop(Looper.java:123)
06-06 17:14:05.220: E/AndroidRuntime(1301): at android.app.ActivityThread.main(ActivityThread.java:4627)
06-06 17:14:05.220: E/AndroidRuntime(1301): at java.lang.reflect.Method.invokeNative(Native Method)
06-06 17:14:05.220: E/AndroidRuntime(1301): at java.lang.reflect.Method.invoke(Method.java:521)
06-06 17:14:05.220: E/AndroidRuntime(1301): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
06-06 17:14:05.220: E/AndroidRuntime(1301): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
06-06 17:14:05.220: E/AndroidRuntime(1301): at dalvik.system.NativeStart.main(Native Method)