为什么我会收到第 92 行是无法访问的语句的错误？
错误在这一行：
final RadioButton r1 = (RadioButton) getView().findViewById(R.id.radio1);
Code:
public class TabFragmentA extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (container == null) {
return null;
}
return (RelativeLayout) inflater.inflate(R.layout.tab_layout_a, container, false);
final RadioButton r1 = (RadioButton) getView().findViewById(R.id.radio1); //the error is here
final RadioButton r2 = (RadioButton) getView().findViewById(R.id.radio2);
final ImageView iv1 = (ImageView) getView().findViewById(R.id.iv1);
final ImageView iv2 = (ImageView) getView().findViewById(R.id.iv2);
iv1.setVisibility(View.INVISIBLE);
iv2.setVisibility(View.INVISIBLE);
r1.setOnCheckedChangeListener(new OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// TODO Auto-generated method stub
if(r1.isChecked())
{
r2.setChecked(false);
iv2.setVisibility(View.INVISIBLE);
iv1.setVisibility(View.VISIBLE);
}
}
});
r2.setOnCheckedChangeListener(new OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// TODO Auto-generated method stub
if(r2.isChecked())
{
r1.setChecked(false);
iv1.setVisibility(View.INVISIBLE);
iv2.setVisibility(View.VISIBLE);
}
}
});
}
}
日志猫错误：
01-23 02:43:31.082 1903-1903/br.com.eddboytools.PreDim E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: br.com.eddboytools.PreDim, PID: 1903
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at br.com.eddboytools.PreDim.TabFragmentA.onCreateView(TabFragmentA.java:29)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1478)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
at android.view.View.measure(View.java:17430)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:875)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at com.android.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:447)
at android.view.View.measure(View.java:17430)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
at android.view.View.measure(View.java:17430)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
at android.view.Choreographer.doCallbacks(Choreographer.java:580)
at android.view.Choreographer.doFrame(Choreographer.java:550)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
01-23 02:43:31.094 1903-1915/br.com.eddboytools.PreDim I/art﹕ Background partial concurrent mark sweep GC freed 261(11KB) AllocSpace objects, 0(0B) LOS objects, 27% free, 1328KB/1840KB, paused 20.856ms total 51.174ms
我们不放return声明高于任何其他声明，除非return处于任何条件语句下。如果我们这样做，那么下面的所有语句将永远不会被执行（意味着它在所有情况下都将变得无法访问），这会导致您收到错误。
像这样做
public class TabFragmentA extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
RelativeLayout rootView = (RelativeLayout) inflater.inflate(R.layout.tab_layout_a, container, false);
final RadioButton r1 = (RadioButton) rootView.findViewById(R.id.radio1);
final RadioButton r2 = (RadioButton) rootView.findViewById(R.id.radio2);
final ImageView iv1 = (ImageView) rootView.findViewById(R.id.iv1);
final ImageView iv2 = (ImageView) rootView.findViewById(R.id.iv2);
iv1.setVisibility(View.INVISIBLE);
iv2.setVisibility(View.INVISIBLE);
r1.setOnCheckedChangeListener(new OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// TODO Auto-generated method stub
if(r1.isChecked())
{
r2.setChecked(false);
iv2.setVisibility(View.INVISIBLE);
iv1.setVisibility(View.VISIBLE);
}
}
});
r2.setOnCheckedChangeListener(new OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// TODO Auto-generated method stub
if(r2.isChecked())
{
r1.setChecked(false);
iv1.setVisibility(View.INVISIBLE);
iv2.setVisibility(View.VISIBLE);
}
}
});
return rootView;
}
}
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