我有一个活动,上面有一个片段,里面有一个TextView。在CourseFragment.java中,我做了一个简单的方法来更改TextView的文本。但是,当我尝试从Activity调用片段的方法时,它说TextView对象为null。这是我的一些代码:
CourseFragment.java
public class CourseFragment extends Fragment {
private Subject subject;
View rootView;
private TextView title;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
rootView = inflater.inflate(R.layout.fragment_course, container,
false);
title = (TextView) rootView.findViewById(R.id.course_title);
return rootView;
}
public void setTitle() {
title.setText("My Title");
}
}
这是我活动中的代码,该代码将创建新片段并将其放置在正确的位置:
CourseFragment fragment = new CourseFragment();
FragmentManager fm = getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.course1, fragment);
fragment.setTitle();
ft.addToBackStack(null);
ft.commit();
来自片段内部的setTitle()方法的错误
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
这似乎很简单,但我不明白为什么我会继续获得NPE。我查看了与此类似的问题,并尝试了所有公认的解决方案,但无济于事。有什么想法吗?
预先感谢
编辑:这是根据要求提供的更多代码:
fragment_course.xml]的开头]
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/course_fragment" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.stagenda.stagenda.CourseFragment" android:padding="16dp" android:orientation="vertical" android:background="@android:color/background_light"> <RelativeLayout android:layout_width="match_parent" tools:ignore="UselessParent" android:background="@color/colorAccent" android:padding="16dp" android:layout_height="wrap_content" android:id="@+id/course_container"> <TextView android:text="Course Given Title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/course_given_title" android:textColor="@android:color/background_light" android:textSize="18sp" /> <TextView android:text="Course Title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/course_title" android:layout_below="@+id/course_given_title" android:textColor="@android:color/background_light" /> <TextView android:text="Course Code" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/course_code" android:textColor="@android:color/background_light" android:layout_toRightOf="@+id/course_title" android:layout_below="@+id/course_given_title" android:layout_alignParentEnd="false" android:layout_marginStart="10dp" />
完整错误:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.stagenda.stagenda, PID: 1654
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5639)
at android.view.View$PerformClick.run(View.java:22387)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6088)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5639)
at android.view.View$PerformClick.run(View.java:22387)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6088)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.stagenda.stagenda.CourseFragment.setTitle(CourseFragment.java:34)
at com.stagenda.stagenda.MainPage.confirmAddCourse(MainPage.java:435)
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5639)
at android.view.View$PerformClick.run(View.java:22387)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6088)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
I/Process: Sending signal. PID: 1654 SIG: 9
Disconnected from the target VM, address: 'localhost:8612', transport: 'socket'
我有一个活动,上面有一个片段,里面有一个TextView。在CourseFragment.java中,我做了一个简单的方法来更改TextView的文本。但是,当我尝试调用片段的...
采用此方法。
我自己弄清楚了。问题出在这里:
片段事务不同步。当您添加事务时,可以在主循环程序有机会运行该事务时执行它(该事务将排队等待稍后)。
选项卡的布局:
您可以做的一件事就是将数据作为参数传递:
如此处http://developer.android.com/training/basics/fragments/communicating.html中所述,通过使用Framgnet回调]解决了这个问题,我认为最好的方法是在创建片段TextView之后将其传递到我的活动中。
onCreateView()
方法在fragmentTransaction.commit()
之后被调用。因为您要在setTitle()
之前调用fragmentTransaction.commit()
,所以不会实例化TextView实例title
,因此为null。在fragment.setTitle()
之后添加fragmentTransaction.commit()
行。