当我抓住NPE时,我正在为课程做作业。无法解决此问题几天,无法修复。谷歌没有帮助。 更新代码 这是我的代码:
MainActivity
// try to use mysqli_* instead of mysql_* functions, mysqli_query() expects parameter 1 to be a database connection resource
$res = mysqli_query($connection, "SELECT name, nickname FROM Horseinfo WHERE name = '$somevariable'");
if ($res && mysqli_num_rows($res)>0) {
$row = mysqli_fetch_row($res);
$horseName= empty($row['nickname']) ? $row['name'] : $row['nickname'];
?>
<div style='font-size:18px; padding-bottom:3px; margin-top:0px;'>records for <? echo horseName;?></div>
<?php } ?>
自拍:
List<Selfie> selfies = new ArrayList<Selfie>();
private CustomAdapter ADAPTER = new CustomAdapter(this, selfies);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
protected void onResume() {
super.onResume();
File youDir = new File("/sdcard/DailySelfie/");
outer : for (File f : youDir.listFiles()) {
//try to find selfie in files
if (f.isFile()) {
for (Selfie selfie : selfies) {
if (selfie.getSelfieName() == f.getName()) {
continue outer;
}
else { continue;}
}
//code below works only if file doesn't exist in selfies.
Bitmap myBitmap = BitmapFactory.decodeFile(f.getAbsolutePath());
try {
selfies.add(new Selfie(f.getName(), myBitmap));
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
CustomAdapter:
public class Selfie {
private Bitmap selfieBitmap;
private String selfieName;
public Selfie(String selfieName, Bitmap selfieBitmap) {
this.selfieName = selfieName;
this.selfieBitmap = selfieBitmap;
}
public String getSelfieName() {
return selfieName;
}
public Bitmap getSelfieBitmap() {
return selfieBitmap;
}
}
ADB:
private Context context;
private List<Selfie> selfies = new ArrayList<Selfie>();
public CustomAdapter(Context context, List<Selfie> selfies) {
this.context = context;
this.selfies = selfies;
}
@Override
public int getCount() {
return selfies.size();
}
@Override
public Object getItem(int position) {
return selfies.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup viewGroup) {
Selfie selfie = selfies.get(position);
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View rowView = new View(context);
//get layout from row.xml
rowView = inflater.inflate(R.layout.row, null);
ImageView imageView = (ImageView) rowView.findViewById(R.id.imageView);
imageView.setImageBitmap(selfie.getSelfieBitmap());
TextView textView = (TextView) rowView.findViewById(R.id.text);
textView.setText(selfie.getSelfieName());
}
return convertView;
}
}
似乎我 04-27 13:17:58.792: E/AndroidRuntime(1979): FATAL EXCEPTION: main
04-27 13:17:58.792: E/AndroidRuntime(1979): java.lang.NullPointerException
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.AbsListView.obtainView(AbsListView.java:2179)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.ListView.makeAndAddView(ListView.java:1840)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.ListView.fillDown(ListView.java:675)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.ListView.fillFromTop(ListView.java:736)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.ListView.layoutChildren(ListView.java:1655)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.AbsListView.onLayout(AbsListView.java:2012)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1660)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.LinearLayout.onLayout(LinearLayout.java:1436)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:502)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.View.layout(View.java:14289)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewGroup.layout(ViewGroup.java:4562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1976)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1730)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1004)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5481)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.Choreographer.doCallbacks(Choreographer.java:562)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.Choreographer.doFrame(Choreographer.java:532)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.os.Handler.handleCallback(Handler.java:730)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.os.Handler.dispatchMessage(Handler.java:92)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.os.Looper.loop(Looper.java:137)
04-27 13:17:58.792: E/AndroidRuntime(1979): at android.app.ActivityThread.main(ActivityThread.java:5103)
04-27 13:17:58.792: E/AndroidRuntime(1979): at java.lang.reflect.Method.invokeNative(Native Method)
04-27 13:17:58.792: E/AndroidRuntime(1979): at java.lang.reflect.Method.invoke(Method.java:525)
04-27 13:17:58.792: E/AndroidRuntime(1979): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
04-27 13:17:58.792: E/AndroidRuntime(1979): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-27 13:17:58.792: E/AndroidRuntime(1979): at dalvik.system.NativeStart.main(Native Method)
有一个NPE。在StackOverflow上发现了同样的问题,但没有任何解决方案对我有帮助。
更新:重写了我的代码,现在它已经
lv.setAdapter(ADAPTER);
还有同样的问题 - NPE。我试图移动&#34; lv = ..; ADAPTER = ...&#34;到onResume,试图把它开始onResume - 它没有帮助:(
答案 0 :(得分:1)
添加
private CustomAdapter ADAPTER = new CustomAdapter(this, selfies);
进入onCreate
方法,因为this
上下文用于类方法.i.e。重写为
private CustomAdapter ADAPTER;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ADAPTER = new CustomAdapter(this, selfies);
}
答案 1 :(得分:0)
检查是否返回null以外的任何内容:
ListView lv = (ListView) findViewById(R.id.listView);
可能无法找到列表。
答案 2 :(得分:0)
由于您在ListView lv = (ListView) findViewById(R.id.listView);
中呼叫onResume
,因此尚未调用setContentView
。始终在onResume
之前调用onCreate
,因此您的ListView
目前不在上下文中。因此NullPointerException。
将您的活动代码更改为此
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lv = (ListView) findViewById(R.id.listView);
}
@Override
protected void onResume() {
super.onResume();
}
答案 3 :(得分:0)
当你初步设定新的自定义时,问题在于你已经设定了这个问题....你必须初始化它onCreate()
! (我的意思是MainActivity类)
答案 4 :(得分:0)
我相信NPE与你的ListView
有关。尝试构建您的应用程序,以便声明类变量并在onCreate()
中初始化它们。这样,您稍后会引用它们(就像在onResume()
中那样)。
List<Selfie> selfies;
private CustomAdapter ADAPTER;
ListView lv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
lv = (ListView) findViewById(R.id.listView);
selfies = new ArrayList<Selfie>();
ADAPTER = new CustomAdapter(this, selfies);
lv.setAdapter(ADAPTER);
}
@Override
protected void onResume() {
super.onResume();
/*
*I don't quite see the purpose in this below section,
*as you can account for a null ArrayList in your adapter class
*/
if (ADAPTER.getCount() >= 0) {
lv.setAdapter(ADAPTER);
}
}
另外,为了更好地解释我上面提到的评论,您可以通过将空数据视为getCount()
大小列表来解释适配器0
中的空数据:
getCount() {
if (selfies == null || selfies.isEmpty()) {
return 0;
}
return selfies.size;
}
编辑:如果问题仅限于您的适配器,那么它可能是来自getView()
的NPE。您可以尝试以下代码:
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View rowView;
Selfie selfie = selfies.get(position);
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) parent.getContext().
getSystemService(Context.LAYOUT_INFLATER_SERVICE);
rowView = inflater.inflate(R.layout.row, parent, false);
} else {
rowView = convertView;
}
ImageView imageView = (ImageView) rowView.findViewById(R.id.imageView);
imageView.setImageBitmap(selfie.getSelfieBitmap());
TextView textView = (TextView) rowView.findViewById(R.id.text);
textView.setText(selfie.getSelfieName());
return rowView;
}
答案 5 :(得分:0)
答案 6 :(得分:0)
答案是,在我的getView()代码中,我返回了convertView但却膨胀了rowView。所以convertView保持为null。 PPartisan向我展示了我的错误并给出了工作代码(如下)。为了提高评级我必须有15个声誉,而我没有。请问某人,他的评价和正确答案?
public View getView(int position, View convertView, ViewGroup parent) {
View rowView;
Selfie selfie = selfies.get(position);
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) parent.getContext().
getSystemService(Context.LAYOUT_INFLATER_SERVICE);
rowView = inflater.inflate(R.layout.row, parent, false);
} else {
rowView = convertView;
}
ImageView imageView = (ImageView) rowView.findViewById(R.id.imageView);
imageView.setImageBitmap(selfie.getSelfieBitmap());
TextView textView = (TextView) rowView.findViewById(R.id.text);
textView.setText(selfie.getSelfieName());
return rowView;
}