Android 在片段中使用listview时出现NullPointer异常
我正在活动中实现自定义listview。 代码如下:Android 在片段中使用listview时出现NullPointer异常,android,listview,android-listview,android-fragments,nullpointerexception,Android,Listview,Android Listview,Android Fragments,Nullpointerexception,我正在活动中实现自定义listview。 代码如下: public class ScoreCard extends ActionBarActivity { ArrayList<Song> songs; int score; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(sav
public class ScoreCard extends ActionBarActivity {
ArrayList<Song> songs;
int score;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
songs = intent.getParcelableArrayListExtra("Songs");
score = intent.getIntExtra("Score", 0);
setContentView(R.layout.activity_score_card);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.score_card, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_score_card, container, false);
ListView listView = (ListView) findViewById(R.id.trackList);
ArrayList<String> tracks = new ArrayList<String>();
//Drawable [] art = new Drawable[tracks.size()];
Log.d("Ayush", songs.size()+"");
Log.d("Ayush", score+"");
for(Song out : songs) {
tracks.add(out.gettracktitle());
Log.d("Ayush", out.gettracktitle());
}
ScoreCardList adapter = new ScoreCardList(getActivity(), tracks);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, final View view,
int position, long id) {
view.animate().setDuration(2000).alpha(0)
.withEndAction(new Runnable() {
@Override
public void run() {
view.setAlpha(1);
}
});
}
});
return rootView;
}
}
}
公共类记分卡扩展了ActionBarActivity{
雅乐歌曲;
智力得分;
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
Intent=getIntent();
歌曲=意图。getParcelableArrayListExtra(“歌曲”);
分数=意图。getIntExtra(“分数”,0);
setContentView(R.layout.activity_score_card);
如果(savedInstanceState==null){
getSupportFragmentManager().beginTransaction()
.add(R.id.container,新的占位符片段())
.commit();
}
}
@凌驾
公共布尔onCreateOptions菜单(菜单){
//为菜单充气;这会将项目添加到操作栏(如果存在)。
getMenuInflater().充气(R.menu.score_卡,菜单);
返回true;
}
@凌驾
公共布尔值onOptionsItemSelected(菜单项项){
//处理操作栏项目单击此处。操作栏将
//自动处理Home/Up按钮上的点击,只要
//在AndroidManifest.xml中指定父活动时。
int id=item.getItemId();
if(id==R.id.action\u设置){
返回true;
}
返回super.onOptionsItemSelected(项目);
}
/**
*包含简单视图的占位符片段。
*/
公共类占位符片段扩展了片段{
公共占位符片段(){
}
@凌驾
创建视图上的公共视图(布局、充气机、视图组容器、,
Bundle savedInstanceState){
视图根视图=充气机。充气(R.layout.fragment\u score\u card,container,false);
ListView ListView=(ListView)findViewById(R.id.trackList);
ArrayList轨迹=新建ArrayList();
//Drawable[]艺术=新的Drawable[tracks.size()];
Log.d(“Ayush”,songs.size()+);
Log.d(“Ayush”,分数+”);
用于(歌曲输出:歌曲){
tracks.add(out.gettracktitle());
Log.d(“Ayush”,out.gettracktitle());
}
记分卡列表适配器=新记分卡列表(getActivity(),跟踪);
setAdapter(适配器);
setOnItemClickListener(新的AdapterView.OnItemClickListener(){
@凌驾
public void onItemClick(AdapterView父视图、最终视图、,
内部位置,长id){
view.animate().setDuration(2000).alpha(0)
.withEndAction(新的可运行(){
@凌驾
公开募捐{
视图。setAlpha(1);
}
});
}
});
返回rootView;
}
}
}
应用程序在listView.setAdapter(adapter)行崩溃,表示它导致了空指针异常。在调试模式下,我观察到,在这一行中,对象adapter不是null,但listView是null。从断点继续时,应用程序崩溃。以下是我的适配器的代码:
public class ScoreCardList extends ArrayAdapter<String>{
private final Activity context;
private final ArrayList<String> web;
//private final Drawable[] imageId;
public ScoreCardList(Activity context,
ArrayList<String> web) {
super(context, R.layout.score_card, web);
this.context = context;
this.web = web;
//this.imageId = imageId;
}
@Override
public View getView(int position, View view, ViewGroup parent) {
LayoutInflater inflater = context.getLayoutInflater();
View rowView= inflater.inflate(R.layout.score_card, null, true);
TextView txtTitle = (TextView) rowView.findViewById(R.id.trackName);
//ImageView imageView = (ImageView) rowView.findViewById(R.id.art);
txtTitle.setText(web.get(position));
//imageView.setImageDrawable(imageId[position]);
return rowView;
}
}
公共类记分卡列表扩展了ArrayAdapter{
私人最终活动背景;
私有最终ArrayList网站;
//私有最终可提取[]图像ID;
公共记分卡列表(活动上下文,
ArrayList(web){
超级(上下文、R.layout.score_card、web);
this.context=上下文;
this.web=web;
//this.imageId=imageId;
}
@凌驾
公共视图getView(内部位置、视图视图、视图组父视图){
LayoutInflater充气器=上下文。getLayoutInflater();
视图行视图=充气机。充气(R.layout.score_卡,空,真);
TextView txtTitle=(TextView)rowView.findViewById(R.id.trackName);
//ImageView ImageView=(ImageView)rowView.findViewById(R.id.art);
setText(web.get(position));
//imageView.setImageDrawable(imageId[位置]);
返回行视图;
}
}
请帮忙。谢谢
The application crashes at the line listView.setAdapter(adapter), saying it caused a null pointer exception.
改变这个
ListView listView = (ListView) findViewById(R.id.trackList);
到
改变这个
ListView listView = (ListView) findViewById(R.id.trackList);
到