我最近发现了类似于button.setText（“Hello World”）的代码行;如果您将按钮指定为onCreate（）方法将抛出nullPointerException：
Button button=(Button)findViewById(R.id.myLayout);
这是因为按钮来自的片段在分配按钮之前没有膨胀，从而使按钮为空。所以我了解到我需要将代码放在片段扩展类的onCreateView（）方法中。但是，在我正在制作的应用程序中，我正在onCreate（）中实现此代码：
SharedPreferences activitiesFile = getApplicationContext().getSharedPreferences("Activities", 0);
Set<String> keylist = activitiesFile.getAll().keySet();
for (String s : keylist) {
String active = activitiesFile.getString(s, "");
Button activeName=new Button(this);
activeName.setText(active);
activeName.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,
LayoutParams.WRAP_CONTENT));
LinearLayout layout=(LinearLayout) findViewById(R.id.ActivityList);
activeName.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
FillInInfo(v);
}
});
layout.addView(activeName);
}
除了layout.addView（activeName）之外，一切都是这个代码块完全正常工作;因为我之前提到的nullPointerException。因此，我决定将此代码块放入onCreateView（）来解决问题，但是将此代码放在fragment类中会产生一些语法错误，说“无法对非staic方法进行静态引用”。我尝试从片段类中取走静态，最后，它从一个问题转到另一个问题。所以，我的问题是当它既不在onCreate（）也不在onCreateView（）上时，我应该如何实现这个代码块。 （请记住，整个代码块需要保持在一起）
片段类：
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_manage_day,
container, false);
TextView textView = (TextView) rootView
.findViewById(R.id.section_label);
textView.setText(Integer.toString(getArguments().getInt(
ARG_SECTION_NUMBER)));
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((ManageDay) activity).onSectionAttached(getArguments().getInt(
ARG_SECTION_NUMBER));
}
}
全班代码：
public class ManageDay extends ActionBarActivity implements
NavigationDrawerFragment.NavigationDrawerCallbacks {
/**
* Fragment managing the behaviors, interactions and presentation of the
* navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
/**
* Used to store the last screen title. For use in
* {@link #restoreActionBar()}.
*/
private CharSequence mTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_manage_day);
Intent intent=getIntent();
SharedPreferences activitiesFile = getApplicationContext().getSharedPreferences("Activities", 0);
Set<String> keylist = activitiesFile.getAll().keySet();
for (String s : keylist) {
String active = activitiesFile.getString(s, "");
Button activeName=new Button(this);
activeName.setText(active);
activeName.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,
LayoutParams.WRAP_CONTENT));
LinearLayout layout=(LinearLayout) findViewById(R.id.ActivityList);
activeName.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
FillInInfo(v);
}
});
layout.addView(activeName);
}
mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager()
.findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
}
@Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager
.beginTransaction()
.replace(R.id.container,
PlaceholderFragment.newInstance(position + 1)).commit();
}
public void onSectionAttached(int number) {
switch (number) {
case 1:
mTitle = getString(R.string.title_section1);
break;
case 2:
mTitle = getString(R.string.title_section2);
break;
case 3:
mTitle = getString(R.string.title_section3);
break;
}
}
public void restoreActionBar() {
ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setTitle(mTitle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.manage_day, menu);
restoreActionBar();
return true;
}
return super.onCreateOptionsMenu(menu);
}
@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 static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_manage_day,
container, false);
TextView textView = (TextView) rootView
.findViewById(R.id.section_label);
textView.setText(Integer.toString(getArguments().getInt(
ARG_SECTION_NUMBER)));
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((ManageDay) activity).onSectionAttached(getArguments().getInt(
ARG_SECTION_NUMBER));
}
}
public void CreateActivity(View view){
EditText editText = (EditText) findViewById(R.id.edit_message);
String activity = editText.getText().toString();
Button button=new Button(this);
button.setText(activity);
LinearLayout layout=(LinearLayout) findViewById(R.id.ActivityList);
button.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
FillInInfo(v);
}
});
layout.addView(button);
editText.setText("");
SharedPreferences activitiesFile = getApplicationContext().getSharedPreferences("Activities", 0);
SharedPreferences.Editor editor = activitiesFile.edit();
editor.putString(activity, activity);
editor.apply();
}
public void FillInInfo(View view){
Intent intent=new Intent(this,ActivityInfo.class);
Button button=(Button)view;
String buttonName=button.getText().toString();
intent.putExtra("Name",buttonName);
startActivity(intent);
}
答案 0 :(得分：1)
在调用onCreateView（）之后，视图（在您的情况下＆＃34; ActivityList＆＃34;）不会被充气。
所以在onCreate（）中，它是null。
您必须将此代码块放在onCreateView（）或onViewCreated（）中（在视图正确膨胀后立即调用onViewCreated）。
要解决您遇到的静态问题，您必须告诉我们您的代码中出现此问题的确切位置。