这是使用兼容包的小型Android 2.2测试应用程序。我正在尝试更新列表项选择上另一个活动的另一个片段上的textview。但问题是，每次第一次单击都会返回nullpointer异常，并且只在第二次单击时才会返回其文本。我想知道为什么会发生这种情况，什么是一个好的解决方案。
ListActivity： -
public class ListActivity extends FragmentActivity implements
ListFragment.OnItemSelectedListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
}
@Override
public void onItemSelected(int index) {
// TODO Auto-generated method stub
// Check to see if there is a frame in which to embed the
// detail fragment directly in the containing UI.
View detailsFrame = findViewById(R.id.detailcontainer);
if (detailsFrame != null
&& detailsFrame.getVisibility() == View.VISIBLE) {
DetailFragment detailFragment = (DetailFragment) getSupportFragmentManager()
.findFragmentById(R.id.detailcontainer);
if (detailFragment == null) {
detailFragment = new DetailFragment();
}
// Execute a transaction, replacing any existing fragment
// with this one inside the frame.
getSupportFragmentManager().beginTransaction()
.replace(R.id.detailcontainer, detailFragment).commit();
detailFragment.setTextView(index);
} else {
// Otherwise we need to launch a new activity to display
Intent intent = new Intent(this, DetailActivity.class);
intent.putExtra("index", index);
startActivity(intent);
}
}
}
ListFragment： -
public class ListFragment extends Fragment {
private OnItemSelectedListener listener;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
String[] countries = new String[] { "India", "Pakistan", "Sri Lanka",
"China", "Bangladesh", "Nepal", "Afghanistan", "North Korea",
"South Korea", "Japan" };
View view = inflater.inflate(R.layout.list_fragment, container, false);
ListView listView = (ListView) view.findViewById(R.id.listView);
// Populate list
ArrayAdapter<String> adapter = new ArrayAdapter<String>(
this.getActivity(), android.R.layout.simple_list_item_1,
countries);
listView.setAdapter(adapter);
// operation to do when an item is clicked
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Toast.makeText(getActivity(), "ListItem Number " + position,
Toast.LENGTH_SHORT).show();
listener.onItemSelected(position);
}
});
return view;
}
// Container Activity must implement this interface
public interface OnItemSelectedListener {
public void onItemSelected(int index);
}
// To ensure that the host activity implements this interface
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
if (activity instanceof OnItemSelectedListener) {
listener = (OnItemSelectedListener) activity;
} else {
throw new ClassCastException(activity.toString()
+ " must implemenet ListFragment.OnItemSelectedListener");
}
}
public void operation(int index) {
listener.onItemSelected(index);
}
}
详情活动： -
public class DetailActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
DetailFragment details;
if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE) {
finish();
return;
}
if (savedInstanceState == null) {
// During initial setup, plug in the details fragment.
details = new DetailFragment();
details.setArguments(getIntent().getExtras());
getSupportFragmentManager().beginTransaction()
.add(android.R.id.content, details).commit();
}
Bundle extras = getIntent().getExtras();
int index = extras.getInt("index");
try {
details = (DetailFragment) getSupportFragmentManager()
.findFragmentById(R.id.detailfragment);
details.setTextView(index);
} catch (NullPointerException ex) {
ex.getStackTrace();
}
}
}
DetailFragment： -
public class DetailFragment extends Fragment {
String[] capitals;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (container == null)
return null;
capitals = new String[] { "delhi", "karachi", "colombo", "beijing",
"dhaka", "katmandu", "Afghanistan", "pyongyang", "seoul",
"tokyo" };
View v = inflater.inflate(R.layout.detail_fragment, container, false);
return v;
}
public void setTextView(int index) {
try {
TextView view = (TextView) getView().findViewById(R.id.detailView);
view.setText(capitals[index]);
} catch (NullPointerException ex) {
ex.getStackTrace();
}
}
public int getShownIndex() {
return getArguments().getInt("index", 0);
}
}
更新： - 我正在添加detailFragment xml： -
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:background="@color/lightblue"
android:orientation="vertical" >
<TextView
android:id="@+id/detailView"
android:layout_width="100dp"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:text="@string/detail_frag" />
</RelativeLayout>
答案 0 :(得分：1)
不是在DetailActivity中执行details.setTextView（index），而是在DetailFragment的onActivityCreated中设置TextView的值，同时传递要在Detailactivity中的片段setArgument方法中设置的值......
DetailsFragment details = new DetailsFragment();
details.setArguments(getIntent().getExtras()); // pass the value of text view here
在片段onActivityCreated中通过getArguments（）获取该值并在textview中设置它。
编辑发送值选择加载片段
列表活动
detailFragment = getFragmentbyTag
if(detailFragment == null)
Create Fragment and Add it and Set Arguments here as well
else
detailFragment.setTextView(value); // fragment already loaded no need to set arguments
如果你想每次更换而不是添加一次并使用添加/加载的片段，每次都使用setarguments ....并删除以前的片段并添加新片段（带参数）但添加一次并重新使用是首选每次点击删除和添加/替换
答案 1 :(得分：0)
TextView view = (TextView) findViewById(R.id.detailView);
而不是
TextView view = (TextView) getView().findViewById(R.id.detailView);
答案 2 :(得分：0)
<强> Updated2
只需初始化TextView中的onCreateView()，无需使用参数化创建DetailFragment即可发表评论
检查详细信息对象是否为null，如果为null，则初始化为null，然后调用setTextView()
if(details==null)
details = new DetailFragment(index);
else
setTextView(index);
Text onCreateView()内的TextView并使用了他们的
public class DetailFragment extends Fragment {
String[] capitals;
int index;
private TextView textView;
public DetailFragment(int index){
this.index = index;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (container == null)
return null;
capitals = new String[] { "delhi", "karachi", "colombo", "beijing",
"dhaka", "katmandu", "Afghanistan", "pyongyang", "seoul",
"tokyo" };
View v = inflater.inflate(R.layout.detail_fragment, container, false);
// Initialize textView
textView = (TextView) v.findViewById(R.id.detailView);
setTextView(index); // set value value here for first time
return v;
}
public void setTextView(int index) {
if(textView!=null)
textView.setText(capitals[index]);
}
public int getShownIndex() {
return getArguments().getInt("index", 0);
}
}