findFragmentByTag()使用替代返回null后执行FragmentTransaction()方法 [英] findFragmentByTag() returns null after perform a FragmentTransaction using replace() method
问题描述
我的Android应用程序包含三个片段:A,B和C 。他们在 MainActivity
布局定义的两个集装箱装载。
My Android app consists three fragments: A, B and C. They're loaded in the two containers defined in the MainActivity
layout.
当应用程序启动时,它显示在碎裂的left_container 加载和 fragmentC在right_container 。
When the app is started, it shows the fragmentA loaded in the left_container and the fragmentC in the right_container.
如果您preSS在碎裂按钮,一个 FragmentTransaction
修改 FragmentC 按 FragmentB 。
If you press the button in the fragmentA, a FragmentTransaction
changes FragmentC by FragmentB.
目前,一切就OK了。 但是当我尝试使用得到的引用,加载fragmentB出现的麻烦 findFragmentByTag()
,因为它返回空
。我用的方法替换 FragmentTransaction
然后我把完成了它的commit()
,但有ISN T方法来调用 FragmentB 方式。我的code:
At the moment everything OK. But the trouble appears when I try to get a reference to the loaded fragmentB using findFragmentByTag()
, because it returns null
. I've used the method replace in the FragmentTransaction
and I've finished it with commit()
, but there isn't way to call FragmentB method. My code:
MainActivity.java:
MainActivity.java:
public class MainActivity extends Activity{
static String fragmentTag = "FRAGMENTB_TAG";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Adds the left container's fragment
getFragmentManager().beginTransaction().add(R.id.left_container, new FragmentA()).commit(); //Adds the fragment A to the left container
//Adds the right container's fragment
getFragmentManager().beginTransaction().add(R.id.right_container, new FragmentC()).commit(); //Adds the Fragment C to the right container
}
/**
* Called when the button "Activate Fragment B" is pressed
*/
public void buttonListener(View v){
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.replace(R.id.right_container, new FragmentB(),fragmentTag); //Replaces the Fragment C previously in the right_container with a new Fragment B
ft.commit(); //Finishes the transaction
//!!HERE THE APP CRASHES (java.lang.NullPointerException = findFragmentByTag returns null
((FragmentB) getFragmentManager().findFragmentByTag(fragmentTag)).testView();
}
}
FragmentB.java:
FragmentB.java:
public class FragmentB extends Fragment {
public View onCreateView(LayoutInflater inflater,
ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_b, container,false);
}
/**
* Gets a reference to the text_fragment_b TextView and calls its method setText(), changing "It doesn't work" text by "It works!"
*/
public void testView(){
TextView tv = (TextView)getView().findViewById(R.id.text_fragment_b);
tv.setText("It works!");
}
}
activity_main.xml:
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<FrameLayout android:id="@+id/left_container" android:layout_width="0px" android:layout_weight="50" android:layout_height="match_parent"/>
<FrameLayout android:id="@+id/right_container" android:layout_width="0px" android:layout_weight="50" android:layout_height="match_parent"/>
</LinearLayout>
fragment_b.xml:
fragment_b.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:layout_margin="5sp">
<TextView
android:id="@+id/text_fragment_b"
android:text="It doesn't works!"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
请帮帮我!我在Android开发的初学者!
Please help me! I'm a beginner in Android development!
推荐答案
我已经解决了!我叫 getSupportFragmentManager()。executePendingTransactions()
做交易后,它的工作!调用该方法后,我可以同时使用 findFragmentById()
和 findFragmentByTag()
mehthods片段。
I've fixed it! I called getSupportFragmentManager().executePendingTransactions()
after doing the transaction and it worked! After calling that method I can get the fragment using both findFragmentById()
and findFragmentByTag()
mehthods.
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