活动开始从片段导致NullPointerException异常 [英] Starting Activity from Fragment causes NullPointerException
问题描述
我在这里坚持了开始从片段内按钮的活动的一个问题。 这是我的code:
I'm stuck here with a problem starting an activity from a Button inside a Fragment. Here is my code:
ViewPagerAdapter.java
import java.util.List;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
public class ViewPagerAdapter extends FragmentPagerAdapter {
private List<Fragment> fragments;
public ViewPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
super(fm);
this.fragments = fragments;
}
@Override
public int getCount() {
return this.fragments.size();
}
@Override
public Fragment getItem(int position) {
return this.fragments.get(position);
}
}
ViewPagerActivity.java
import java.util.List;
import java.util.Vector;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.util.Log;
import com.package.here.Class1Overview;
import com.package.here.Class1Overview;
import com.package.here.Class1Overview;
public class ViewPagerActivity extends FragmentActivity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
super.setContentView(R.layout.viewpager);
ViewPager pager = (ViewPager)super.findViewById(R.id.my_viewpager);
pager.setAdapter(initialisePaging());
}
private ViewPagerAdapter initialisePaging() {
List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this, Class1Overview.class.getName()));
fragments.add(Fragment.instantiate(this, Class2Overview.class.getName()));
fragments.add(Fragment.instantiate(this, Class3Overview.class.getName()));
return new ViewPagerAdapter(super.getSupportFragmentManager(), fragments);
}
}
Class1Overview.java (这里是按钮)
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.LinearLayout;
import com.package.here.R;
public class FuelOverview extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (container == null) {
return null;
}
View v = (LinearLayout)inflater.inflate(R.layout.class_one_layout, container, false);
View AddBtn = v.findViewById(R.id.btn_add);
((Button) AddBtn).setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent();
intent.setClass(getActivity(), ActivityToStart.class);
startActivity(intent);
}
});
return v;
}
}
这是我的 LogCat中
01-05 19:39:00.913: E/AndroidRuntime(10557): Uncaught handler: thread main exiting due to uncaught exception
01-05 19:39:01.034: E/AndroidRuntime(10557): java.lang.RuntimeException: Unable to pause activity {com.package.here/com.package.here.ViewPagerActivity}: java.lang.NullPointerException
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3162)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3119)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:3102)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread.access$2400(ActivityThread.java:119)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1870)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.os.Handler.dispatchMessage(Handler.java:99)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.os.Looper.loop(Looper.java:123)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread.main(ActivityThread.java:4363)
01-05 19:39:01.034: E/AndroidRuntime(10557): at java.lang.reflect.Method.invokeNative(Native Method)
01-05 19:39:01.034: E/AndroidRuntime(10557): at java.lang.reflect.Method.invoke(Method.java:521)
01-05 19:39:01.034: E/AndroidRuntime(10557): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
01-05 19:39:01.034: E/AndroidRuntime(10557): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
01-05 19:39:01.034: E/AndroidRuntime(10557): at dalvik.system.NativeStart.main(Native Method)
01-05 19:39:01.034: E/AndroidRuntime(10557): Caused by: java.lang.NullPointerException
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.support.v4.app.FragmentManagerImpl.saveFragmentBasicState(FragmentManager.java:1576)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.support.v4.app.FragmentManagerImpl.saveAllState(FragmentManager.java:1617)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.support.v4.app.FragmentActivity.onSaveInstanceState(FragmentActivity.java:481)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.Activity.performSaveInstanceState(Activity.java:1022)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1180)
01-05 19:39:01.034: E/AndroidRuntime(10557): at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3144)
01-05 19:39:01.034: E/AndroidRuntime(10557): ... 12 more
01-05 19:39:01.423: I/dalvikvm(10557): threadid=7: reacting to signal 3
ViewPager本身是工作的罚款。这似乎是一个错误暂停FragmentActivity,但我不能弄明白。我发现的唯一的事情是这个职位上谷歌<一href="http://$c$c.google.com/p/android/issues/detail?id=19917">http://$c$c.google.com/p/android/issues/detail?id=19917
我也得到了通过谷歌的例子code,以确保我主要是使用相同的技术......
I also got through the google example code to make sure I mainly use the same technique...
编辑:以确保ClickListener的作品,我想敬酒在onclick方法 - 完美的作品
to make sure the ClickListener works, I tried a Toast in the onClick method - works perfectly.
推荐答案
这是一个已知的问题,我很震惊地发现,没有一个人提出一个错误的公共bug跟踪系统这一点。
This is a known problem and I'm shocked to find that no one has filed a bug on the public bug tracker for this.
从此你的问题的根源:
if (f.mSavedViewState != null) {
if (result == null) {
result = new Bundle();
}
result.putSparseParcelableArray(
FragmentManagerImpl.VIEW_STATE_TAG, f.mSavedViewState);
}
if (!f.mUserVisibleHint) {
// Only add this if it's not the default value
result.putBoolean(FragmentManagerImpl.USER_VISIBLE_HINT_TAG, f.mUserVisibleHint);
}
您应该注意到,如果结果
是空
进入该code和第一个如果
则不会触发,你会得到一个 NullPointerException异常
如果我们进入第二个如果
。
You should notice that if result
is null
coming into this code and the first if
is not triggered you'll get a NullPointerException
if we enter the second if
.
它应该阅读:
if (f.mSavedViewState != null) {
if (result == null) {
result = new Bundle();
}
result.putSparseParcelableArray(
FragmentManagerImpl.VIEW_STATE_TAG, f.mSavedViewState);
}
if (!f.mUserVisibleHint) {
if (result == null) {
result = new Bundle();
}
// Only add this if it's not the default value
result.putBoolean(FragmentManagerImpl.USER_VISIBLE_HINT_TAG, f.mUserVisibleHint);
}
我提交了一个补丁,这一个星期或两个前:<一href="https://android-review.googlesource.com/31261">https://android-review.googlesource.com/31261
这篇关于活动开始从片段导致NullPointerException异常的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!