android - 如何从 Android fragment 更新 XML TextView？

Question

我正在尝试从 FragmentActivity 更新 fragment 的 TextView 的文本。在 else 语句中，我首先创建了一个 Fragment，然后我用 updateItemView() 更新了 TextView > 属于该 fragment 的方法，但我得到的只是一个空指针异常。

我可以从 if 语句更新 TextView 但为什么我不能更新 TextView来自 else 语句？

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");
    }
}

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>

最后是我用来替换 fragment 的 FrameLayout:

<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

Answer 1

当您调用 commit 时，该 Fragment 事务不会立即完成，因此当您调用 updateItemView() 时，无法立即找到 TextView。尝试使用 FragmentManager.executePendingTransaction()强制进行交易:

//...
transaction.addToBackStack(null);
transaction.commit();
getSupportFragmentManager().executePendingTransaction();
secondFragment.updateItemView();