所以,现在我有一个用虚拟条目填充ListView的活动。然后我将OnScrollListener设置为列表。这很好。
代码:
public class MainActivity extends ActionBarActivity {
ListView listView;
ArrayList<Location> arrayOfLocations;
LocationAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
listView = (ListView) findViewById(R.id.listView1);
// progress = (ProgressBar) findViewById(R.id.progressbar_loading);
progress = new ProgressDialog(this);
// Construct the data source
arrayOfLocations = new ArrayList<Location>();
// Create the adapter to convert the array to views
adapter = new LocationAdapter(this, arrayOfLocations);
adapter.add(new Location(null, "Title", null, null, null));
adapter.add(new Location(null, "Title", null, null, null));
adapter.add(new Location(null, "Title", null, null, null));
adapter.add(new Location(null, "Title", null, null, null));
adapter.add(new Location(null, "Title", null, null, null));
adapter.add(new Location(null, "Title", null, null, null));
adapter.add(new Location(null, "Title", null, null, null));
listView.setAdapter(adapter);
listView.setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
}
});
}
}
然后,在onScroll里面,我把
if (listView.getLastVisiblePosition() == listView.getAdapter().getCount() - 1
&& listView.getChildAt(listView.getChildCount() - 1).getBottom() <= listView.getHeight()) {
Toast.makeText(getApplicationContext(), "Bottom!",
Toast.LENGTH_LONG).show();
}
在这里,我正在检测当前显示条目的结束,然后显示“Bottom!”但我收到错误,我的应用程序崩溃了
任何想法为什么?谢谢你们
**编辑:** 这是logcat
06-04 14:47:00.670: W/dalvikvm(12719): threadid=1: thread exiting with uncaught exception (group=0x419397c0)
06-04 14:47:00.670: E/AndroidRuntime(12719): FATAL EXCEPTION: main
06-04 14:47:00.670: E/AndroidRuntime(12719): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test6/com.example.test6.MainActivity}: java.lang.NullPointerException
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2389)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.ActivityThread.access$600(ActivityThread.java:153)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1269)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.os.Handler.dispatchMessage(Handler.java:99)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.os.Looper.loop(Looper.java:137)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.ActivityThread.main(ActivityThread.java:5289)
06-04 14:47:00.670: E/AndroidRuntime(12719): at java.lang.reflect.Method.invokeNative(Native Method)
06-04 14:47:00.670: E/AndroidRuntime(12719): at java.lang.reflect.Method.invoke(Method.java:525)
06-04 14:47:00.670: E/AndroidRuntime(12719): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
06-04 14:47:00.670: E/AndroidRuntime(12719): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
06-04 14:47:00.670: E/AndroidRuntime(12719): at dalvik.system.NativeStart.main(Native Method)
06-04 14:47:00.670: E/AndroidRuntime(12719): Caused by: java.lang.NullPointerException
06-04 14:47:00.670: E/AndroidRuntime(12719): at com.example.test6.MainActivity.onCreate(MainActivity.java:62)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.Activity.performCreate(Activity.java:5133)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-04 14:47:00.670: E/AndroidRuntime(12719): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2293)
答案 0 :(得分:1)
我不确定它发生的位置......但只有在我添加时才会发生 我在原帖中列出的第二段代码
我会添加一些空指针检查以确保安全。我怀疑这部分是空的:
listView.getChildAt(listView.getChildCount() - 1)
试试这个:
if (listView.getLastVisiblePosition() == listView.getAdapter().getCount() - 1
&& listView.getChildAt(listView.getChildCount() - 1) != null
&& listView.getChildAt(listView.getChildCount() - 1).getBottom() <= listView.getHeight()) {
Toast.makeText(getApplicationContext(), "Bottom!", Toast.LENGTH_LONG).show();
}
以防你想要进行空指针检查的额外跳跃:
if (listView != null && listView.getAdapter() != null
&& listView.getChildAt(listView.getChildCount() - 1) != null
&& listView.getLastVisiblePosition() == listView.getAdapter().getCount() - 1
&& listView.getChildAt(listView.getChildCount() - 1).getBottom() <= listView.getHeight()) {
Toast.makeText(getApplicationContext(), "Bottom!", Toast.LENGTH_LONG).show();
}