Question

我有一个简单的程序来执行片段替换，获取这个日志错误......如何克服这个
我在这里使用newInstance

MainActivity.java

public class MainActivity extends FragmentActivity {

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


        //First fragment should be mounted on oncreate of main activity
        if (savedInstanceState == null) {  

            Fragment newFragment = FragmentOne.newInstance();  
            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();  
            ft.replace(R.id.container, newFragment).addToBackStack(null).commit();  
        }
    }

}

FragmentOne.java

public class FragmentOne extends Fragment{

    Button btn;

    public static FragmentOne newInstance(){
        FragmentOne fragment = new FragmentOne();
        return  fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View view=inflater.inflate(R.layout.fragment_one, container, false);

        btn=(Button) getActivity().findViewById(R.id.button1);

        return view;
    }

    @Override
    public void onStart() {
        super.onStart();

        btn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                FragmentManager manager = getActivity().getSupportFragmentManager();
                Fragment frgObj=FragmentOne.newInstance();
                FragmentTransaction ft = manager.beginTransaction();
                ft.replace(R.id.container, frgObj,"FragmentOne");
                ft.addToBackStack(null);
                ft.commit();                
            }
        });
    }
}

activity_main.xml中

<LinearLayout 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" 
    android:orientation="vertical"
    android:id="@+id/container">

</LinearLayout>

的日志::

08-09 15:00:50.327: D/AndroidRuntime(769): Shutting down VM
08-09 15:00:50.327: W/dalvikvm(769): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
08-09 15:00:50.357: E/AndroidRuntime(769): FATAL EXCEPTION: main
08-09 15:00:50.357: E/AndroidRuntime(769): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.stylingandroid/com.example.stylingandroid.MainActivity}: java.lang.NullPointerException
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.ActivityThread.access$600(ActivityThread.java:122)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.os.Looper.loop(Looper.java:137)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.ActivityThread.main(ActivityThread.java:4340)
08-09 15:00:50.357: E/AndroidRuntime(769):  at java.lang.reflect.Method.invokeNative(Native Method)
08-09 15:00:50.357: E/AndroidRuntime(769):  at java.lang.reflect.Method.invoke(Method.java:511)
08-09 15:00:50.357: E/AndroidRuntime(769):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-09 15:00:50.357: E/AndroidRuntime(769):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-09 15:00:50.357: E/AndroidRuntime(769):  at dalvik.system.NativeStart.main(Native Method)
08-09 15:00:50.357: E/AndroidRuntime(769): Caused by: java.lang.NullPointerException
08-09 15:00:50.357: E/AndroidRuntime(769):  at com.example.stylingandroid.FragmentOne.onStart(FragmentOne.java:37)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.support.v4.app.Fragment.performStart(Fragment.java:1524)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:968)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1097)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.support.v4.app.FragmentManagerImpl.dispatchStart(FragmentManager.java:1900)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:587)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1133)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.Activity.performStart(Activity.java:4475)
08-09 15:00:50.357: E/AndroidRuntime(769):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1928)
08-09 15:00:50.357: E/AndroidRuntime(769):  ... 11 more

Answer 1

您的Fragment View未附加到Activity onCreateView()方法，因此btn为null 改变这一行

   btn=(Button) getActivity().findViewById(R.id.button1);

进入

   btn=(Button)view.findViewById(R.id.button1);

否则将该行移至onStart()方法

Android中片段事务的Nullpointer异常

1 个答案: