java - getArgument() 始终为 null

Question

我知道这个问题已经被问了一遍又一遍，但我无法做到这一点。

我只想将参数从 Activity 传递到 Fragment。我已经尝试了网上能找到的所有方法，但无法使其工作。我总是收到 NullPointerException 错误。我什至尝试过测试代码，结果相同。所以这里是:

MainActivity.java:

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Bundle bundle = new Bundle();
        bundle.putString("my_key", "My String");
        MyFragment myFrag = new MyFragment();
        myFrag.setArguments(bundle);
    }
}

MyFragment.java

public class MyFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragmentlayout, container, false);
        TextView text = (TextView) view.findViewById(R.id.game);
        String getArgument = getArguments().getString("my_key");
        text.setText(getArgument);
        return view;
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.test.test.MainActivity">

<fragment
    android:id="@+id/fragment_game"
    class="com.example.test.test.MyFragment"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    tools:layout="@layout/fragmentlayout" />

</FrameLayout>

fragmentlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/fragment_game"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
tools:context=".MyFragment" >

    <TextView
        android:id="@+id/game"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textColor="#411124"
        />
</LinearLayout>

错误

FATAL EXCEPTION: main
                                                                     Process: com.example.test.test, PID: 11917
                                                                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test.test/com.example.test.test.MainActivity}: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class fragment
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                         at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                         at android.os.Looper.loop(Looper.java:154)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                                      Caused by: android.view.InflateException: Binary XML file line #9: Binary XML file line #9: Error inflating class fragment
                                                                      Caused by: android.view.InflateException: Binary XML file line #9: Error inflating class fragment
                                                                      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
                                                                         at com.example.test.test.MyFragment.onCreateView(MyFragment.java:20)
                                                                         at android.app.Fragment.performCreateView(Fragment.java:2353)
                                                                         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:959)
                                                                         at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1149)
                                                                         at android.app.FragmentManagerImpl.addFragment(FragmentManager.java:1251)
                                                                         at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2311)
                                                                         at android.app.FragmentController.onCreateView(FragmentController.java:98)
                                                                         at android.app.Activity.onCreateView(Activity.java:5901)
                                                                         at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:777)
                                                                         at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
                                                                         at android.view.LayoutInflater.rInflate(LayoutInflater.java:858)
                                                                         at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
                                                                         at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
                                                                         at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
                                                                         at android.view.LayoutInflater.inflate(LayoutInflater.java:377)
                                                                         at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:412)
                                                                         at android.app.Activity.setContentView(Activity.java:2414)
                                                                         at com.example.test.test.MainActivity.onCreate(MainActivity.java:12)
                                                                         at android.app.Activity.performCreate(Activity.java:6679)
                                                                         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                                         at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                         at android.os.Looper.loop(Looper.java:154)
                                                                         at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                         at java.lang.reflect.Method.invoke(Native Method)
                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

如何获取参数而不报错？

Answer 1

您的代码有 2 个问题，a) 您正在实例化 Fragment以编程方式但您没有将其附加到 Activity ，所以它完全没用，并且b)您还实例化了 Fragment在 xml 布局中 Fragment将没有机会在 onCreateView 之前设置参数叫做。因此，如果需要删除Fragment从 xml 中，在 Activity.onCreate 中创建一个实例，设置参数，然后将其附加到 Activity与 FragmentManager

更改activity_main.xml对此(请注意 android:id 属性)

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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/fragment_container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.test.test.MainActivity">    

</FrameLayout>

以及onCreate的MainActivity

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Bundle bundle = new Bundle();
bundle.putString("my_key", "My String");
MyFragment myFrag = new MyFragment();
myFrag.setArguments(bundle);
getFragmentManager().beginTransaction()
    .add(R.id.fragment_container, myFrag, "myFrag")
    .commit();