[英]ListView.setAdapter NullPointerException
當我參加NPE時,我正在做Coursera課程的作業。 幾天無法解決此問題,如果不解決就無法繼續。 Google沒有幫助。 頁面下方的更新代碼這是我的代碼:
主要活動
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();
}
}
}
}
自拍:
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;
}
}
CustomAdapter:
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;
}
}
亞行:
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)
似乎我在lv.setAdapter(ADAPTER);
處有NPE lv.setAdapter(ADAPTER);
。 在StackOverflow上發現了相同的問題,但是沒有解決方案對我有幫助。 更新:重寫了我的代碼,所以現在
List<Selfie> selfies;
ListView lv;
private CustomAdapter ADAPTER;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
selfies = new ArrayList<Selfie>();
lv = (ListView) findViewById(R.id.listView);
ADAPTER = new CustomAdapter(this, selfies);
}
@Override
protected void onResume() {
super.onResume();
...
lv.setAdapter(ADAPTER);
}
仍然有同樣的問題-NPE。 我試圖將“ lv = ..; ADAPTER = ...”移動到onResume,試圖將其放在onResume的開頭-它沒有幫助:(
加
private CustomAdapter ADAPTER = new CustomAdapter(this, selfies);
進入onCreate
方法,因為this
上下文在類method.ie中使用
private CustomAdapter ADAPTER;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ADAPTER = new CustomAdapter(this, selfies);
}
檢查是否返回null以外的任何內容:
ListView lv = (ListView) findViewById(R.id.listView);
可能是找不到列表。
由於您正在調用ListView lv = (ListView) findViewById(R.id.listView);
在onResume
,尚未調用setContentView
。 onResume
總是在onCreate
之前調用,因此您的ListView
當前不在上下文中。 因此,NullPointerException。
將您的活動代碼更改為此
@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();
}
問題在於初始化新的Custom時您已經設置了這個問題。...您必須在onCreate()
上初始化它! (我的意思是MainActivity類)
我相信NPE與您的ListView
。 嘗試構建您的應用程序,以便您聲明類變量並在onCreate()
對其進行初始化。 這樣,您稍后就可以引用它們(就像在onResume()
)。
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,為了更好地解釋我在上面所做的評論,可以通過將空數據視為0
大小列表來說明適配器getCount()
的空數據:
getCount() {
if (selfies == null || selfies.isEmpty()) {
return 0;
}
return selfies.size;
}
編輯:如果問題僅限於您的適配器,則可能是來自getView()
的NPE。 您可以嘗試以下代碼:
@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;
}
您的自拍照數組列表為空,因為我什么都沒看到? 而且您的班級自拍照只具有吸氣劑,而沒有二傳手,那么您如何將自拍照設置為自拍照的數組列表?
答案是,在我的getView()代碼中,我返回了convertView但又誇大了rowView。 因此convertView保持為空。 PPartisan向我展示了我的錯誤並提供了有效的代碼(如下)。 要提高等級,我必須有15個聲譽,而我沒有。 有人可以提高他的評分和正確答案嗎?
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;
}
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