我正在尝试从
FragmentActivity
中更新片段的TextView
文本。在else
语句中,我首先创建了一个Fragment
,然后使用属于该片段的updateItemView()
方法更新TextView
,但是我得到的结果是空指针异常。
我可以从if
语句中更新TextView
,但为什么无法从else
语句中更新TextView
?
这是FragmentActivity
的代码:
public void toDeatailsBtn(View view){
ItemFragment listFragment = (ItemFragment) getSupportFragmentManager()
.findFragmentById(R.id.large_layout_list_item_fragment);
if(listFragment != null){
//The "if" code is working.
listFragment.updateItemView();
}
// I'm swaping fragments here. I already added firstFragment to the
//fragment_container FrameLayout in other code.
else{
ItemFragment secondFragment = new ItemFragment();
FragmentTransaction transaction =
getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragment_container, secondFragment);
transaction.addToBackStack(null);
transaction.commit();
//This is giving me the null pointer exception, even though
//secondFragment has been created in theory.
secondFragment.updateItemView();
}
}
包含 updateItemView()
方法的 Fragment
:
public class ItemFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.item_fragment, container, false);
}
public void updateItemView(){
TextView name = (TextView) getActivity()
.findViewById(R.id.list_item_fragment);
name.setText("TEST");
}
}
The TextView
:
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:id="@+id/list_item_fragment"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:freezesText="true" />
</LinearLayout>
</ScrollView>
最后,我使用的FrameLayout
来替换片段:
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/fragment_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:context=".MainFragmentActivity" />
错误日志:
01-06 00:59:08.425: E/AndroidRuntime(1610): java.lang.IllegalStateException: Could not execute method of the activity
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.view.View$1.onClick(View.java:3591)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.view.View.performClick(View.java:4084)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.view.View$PerformClick.run(View.java:16966)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.os.Handler.handleCallback(Handler.java:615)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.os.Handler.dispatchMessage(Handler.java:92)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.os.Looper.loop(Looper.java:137)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.app.ActivityThread.main(ActivityThread.java:4745)
01-06 00:59:08.425: E/AndroidRuntime(1610): at java.lang.reflect.Method.invokeNative(Native Method)
01-06 00:59:08.425: E/AndroidRuntime(1610): at java.lang.reflect.Method.invoke(Method.java:511)
01-06 00:59:08.425: E/AndroidRuntime(1610): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-06 00:59:08.425: E/AndroidRuntime(1610): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-06 00:59:08.425: E/AndroidRuntime(1610): at dalvik.system.NativeStart.main(Native Method)
01-06 00:59:08.425: E/AndroidRuntime(1610): Caused by: java.lang.reflect.InvocationTargetException
01-06 00:59:08.425: E/AndroidRuntime(1610): at java.lang.reflect.Method.invokeNative(Native Method)
01-06 00:59:08.425: E/AndroidRuntime(1610): at java.lang.reflect.Method.invoke(Method.java:511)
01-06 00:59:08.425: E/AndroidRuntime(1610): at android.view.View$1.onClick(View.java:3586)
01-06 00:59:08.425: E/AndroidRuntime(1610): ... 11 more
01-06 00:59:08.425: E/AndroidRuntime(1610): Caused by: java.lang.NullPointerException
01-06 00:59:08.425: E/AndroidRuntime(1610): at com.site.myapp.ItemFragment.updateItemView(ItemFragment.java:27)
01-06 00:59:08.425: E/AndroidRuntime(1610): at com.site.myapp.MainFragmentActivity.toDetailsBtn(MainFragmentActivity.java:90)
01-06 00:59:08.425: E/AndroidRuntime(1610): ... 14 more
commit()
后事务没有立即完成。 - user1952398Fragment
系统的设计方式,异步执行。此外,你可能只需要从其中一个Fragment
的回调函数中调用updateItemView
,而不是从外部调用,因为调用该方法更像是一个初始化过程。我不明白为什么你的问题会被投票降低,它提问得很好,而且你还提供了相关的代码和异常堆栈跟踪信息。 - user