我是 android 新手，我试图让 editText 在选择项目时变得可见，代码似乎很好，但是只要我运行应用程序并单击访问该活动的按钮，模拟器就会停止工作。这是我的代码：
import java.util.Locale;
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public class ManageActivity extends FragmentActivity implements
ActionBar.TabListener {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
* will keep every loaded fragment in memory. If this becomes too memory
* intensive, it may be best to switch to a
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*/
SectionsPagerAdapter mSectionsPagerAdapter;
/**
* The {@link ViewPager} that will host the section contents.
*/
ViewPager mViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_manage);
// Set up the action bar.
final ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Create the adapter that will return a fragment for each of the three
// primary sections of the app.
mSectionsPagerAdapter = new SectionsPagerAdapter(
getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
// When swiping between different sections, select the corresponding
// tab. We can also use ActionBar.Tab#select() to do this if we have
// a reference to the Tab.
mViewPager
.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by
// the adapter. Also specify this Activity object, which implements
// the TabListener interface, as the callback (listener) for when
// this tab is selected.
actionBar.addTab(actionBar.newTab()
.setText(mSectionsPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.manage, menu);
return true;
}
@Override
public void onTabSelected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
// When the given tab is selected, switch to the corresponding page in
// the ViewPager.
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabReselected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a NewCaseFragment (defined as a static inner class
// below) with the page number as its lone argument.
if(position == 0){
Fragment fragment = new NewCaseFragment();
//Bundle args = new Bundle();
//args.putInt(NewCaseFragment.ARG_SECTION_NUMBER, position + 1);
//fragment.setArguments(args);
return fragment;
}
else{
Fragment fragment = new UpdateFragment();
return fragment;
}
}
@Override
public int getCount() {
// Show 3 total pages.
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.title_section1).toUpperCase(l);
case 1:
return getString(R.string.title_section2).toUpperCase(l);
case 2:
return getString(R.string.title_section3).toUpperCase(l);
}
return null;
}
}
/**
* A fragment representing a section of the app
*/
public static class NewCaseFragment extends Fragment implements OnItemSelectedListener{
public NewCaseFragment() {
}
Button members ;
EditText orgname , orgaddress;
//Spinner spinner1;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.newcase,
container, false);
Button members = (Button)getActivity(). findViewById(R.id.members);
EditText orgname = (EditText)getActivity(). findViewById(R.id.orgname);
EditText orgaddress = (EditText)getActivity(). findViewById(R.id.orgaddress);
Spinner spinner1 = (Spinner)getActivity(). findViewById(R.id.spinner1);
spinner1.setOnItemSelectedListener(this);
//members.setOnClickListener(membersListener);
return rootView;
}
public void onItemSelected(AdapterView<?> spinner1, View view,int pos, long id)
{
orgname.setVisibility(View.VISIBLE);
orgaddress.setVisibility(View.VISIBLE);
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
}
/*******
*
*/
public static class UpdateFragment extends Fragment {
public UpdateFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.updatecase,
container, false);
return rootView;
}
}
}
布局 ：
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/scroller"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fillViewport="true" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.01"
android:orientation="horizontal"
android:padding="10dp" >
<EditText
android:id="@+id/casename"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:ems="10"
android:hint="@string/casename"
android:inputType="text"
android:textSize="12sp" >
<requestFocus />
</EditText>
</LinearLayout>
<Spinner
android:id="@+id/spinner1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:entries="@array/organisation"
android:prompt="@string/infoorg" />
<!-- layout for organisation information -->
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.01"
android:orientation="horizontal"
android:padding="10dp" >
<EditText
android:id="@+id/orgname"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:hint="@string/orgname"
android:inputType="text"
android:textSize="12sp"
android:visibility="gone"
/>
</LinearLayout>
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.01"
android:orientation="horizontal"
android:padding="10dp" >
<EditText
android:id="@+id/orgaddress"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:hint="@string/orgaddress"
android:inputType="text"
android:textSize="12sp"
android:visibility="gone"
/>
</LinearLayout>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.01"
android:orientation="horizontal"
android:padding="10dp" >
<TextView
android:id="@+id/staff"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_weight="1.0"
android:clickable="true"
android:hint="@string/staff"
android:textSize="14sp"
android:layout_margin="10dp"
android:textStyle="bold" />
<Button
android:id="@+id/members"
style="@style/btnStyleGrey"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableLeft="@drawable/users2"
android:text="@string/plus"
android:layout_toRightOf="@+id/staff"
/>
</RelativeLayout>
<Button
android:id="@+id/submit"
style="@style/btnStyleBlue"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:text="@string/submit" />
</LinearLayout>
</ScrollView>
这是日志：
05-09 18:01:44.684: E/AndroidRuntime(1480): FATAL EXCEPTION: main
05-09 18:01:44.684: E/AndroidRuntime(1480): java.lang.NullPointerException
05-09 18:01:44.684: E/AndroidRuntime(1480): at com.pfe.risu.ManageActivity$NewCaseFragment.onCreateView(ManageActivity.java:195)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.Fragment.performCreateView(Fragment.java:1460)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:911)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:461)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.view.ViewPager.populate(ViewPager.java:1011)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.view.ViewPager.populate(ViewPager.java:880)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1374)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.View.measure(View.java:12603)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4677)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.View.measure(View.java:12603)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.widget.LinearLayout.measureVertical(LinearLayout.java:812)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.widget.LinearLayout.onMeasure(LinearLayout.java:553)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.View.measure(View.java:12603)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4677)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
05-09 18:01:44.684: E/AndroidRuntime(1480): at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2072)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.View.measure(View.java:12603)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1044)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2418)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.os.Handler.dispatchMessage(Handler.java:99)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.os.Looper.loop(Looper.java:137)
05-09 18:01:44.684: E/AndroidRuntime(1480): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-09 18:01:44.684: E/AndroidRuntime(1480): at java.lang.reflect.Method.invokeNative(Native Method)
05-09 18:01:44.684: E/AndroidRuntime(1480): at java.lang.reflect.Method.invoke(Method.java:511)
05-09 18:01:44.684: E/AndroidRuntime(1480): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-09 18:01:44.684: E/AndroidRuntime(1480): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-09 18:01:44.684: E/AndroidRuntime(1480): at dalvik.system.NativeStart.main(Native Method)
解决第二个问题：
现在我在这些行上得到空指针异常：
orgname.setVisibility(View.VISIBLE);
orgaddress.setVisibility(View.VISIBLE);
II 在 onItemSelected 方法中初始化变量：
public void onItemSelected(AdapterView<?> spinner1, View view,int pos, long id)
{
EditText orgname = (EditText)getActivity().findViewById(R.id.orgname);
EditText orgaddress = (EditText)getActivity().findViewById(R.id.orgaddress);
orgname.setVisibility(View.VISIBLE);
orgaddress.setVisibility(View.VISIBLE);
}
我没有例外，但 ItemSelectedListner 上的似乎没有工作，并且 EditTexts 是可见的:(
更换后
EditText orgname = (EditText)getActivity(). findViewById(R.id.orgname); EditText orgaddress = (EditText)getActivity(). findViewById(R.id.orgaddress);
和
EditText orgname = (EditText)view.findViewById(R.id.orgname);
EditText orgaddress = (EditText)view.findViewById(R.id.orgaddress);
ManageActivity 显示 EditTexts 是不可见的，但随后应用程序再次停止。这是日志：
05-09 20:58:24.401: E/AndroidRuntime(581): FATAL EXCEPTION: main
05-09 20:58:24.401: E/AndroidRuntime(581): java.lang.NullPointerException
05-09 20:58:24.401: E/AndroidRuntime(581): at com.pfe.risu.ManageActivity$NewCaseFragment.onItemSelected(ManageActivity.java:208)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.widget.AdapterView.fireOnSelected(AdapterView.java:882)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.widget.AdapterView.access$200(AdapterView.java:48)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.widget.AdapterView$SelectionNotifier.run(AdapterView.java:848)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.os.Handler.handleCallback(Handler.java:605)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.os.Handler.dispatchMessage(Handler.java:92)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.os.Looper.loop(Looper.java:137)
05-09 20:58:24.401: E/AndroidRuntime(581): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-09 20:58:24.401: E/AndroidRuntime(581): at java.lang.reflect.Method.invokeNative(Native Method)
05-09 20:58:24.401: E/AndroidRuntime(581): at java.lang.reflect.Method.invoke(Method.java:511)
05-09 20:58:24.401: E/AndroidRuntime(581): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-09 20:58:24.401: E/AndroidRuntime(581): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-09 20:58:24.401: E/AndroidRuntime(581): at dalvik.system.NativeStart.main(Native Method)
这是第 208 行：
orgname.setVisibility(View.VISIBLE);