Question

当WIFI连接中断时，我检测到WIFI连接。

它会在所有小部件的顶部显示framelayout。

    public class MjpegPlayerFragment extends Fragment {

    public static FrameLayout reconnect_layout;


private class GetTimeStamp extends AsyncTask<URL, Integer, String> {

        protected void onPostExecute(String result) {
            Activity activity = getActivity() ;
            if (activity != null) {
                reconnect_fragment();

            }
            super.onPostExecute(result) ;
    }
}

         public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
                    View view = inflater.inflate(R.layout.preview_player, container, false) ;
                    reconnect_layout = (FrameLayout) getActivity().findViewById(R.id.reconnect_layout);
                    return view ;
    }


    public static void reconnect_fragment() {
        reconnect_layout.setVisibility(View.VISIBLE);
    }

xml的代码如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:baselineAligned="false"
    android:orientation="vertical" >

    <FrameLayout
        android:id="@+id/reconnect_layout"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:visibility="gone"
        android:background="#454749">

       <RelativeLayout
        android:id="@+id/layout_imgbtn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layout_centerVertical="true"
        android:layout_above="@+id/bottom_buttonlayout"
        android:layout_below="@+id/top_buttonlayout"
        android:orientation="horizontal" >

        <ImageView 
            android:id="@+id/phone"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_toLeftOf="@+id/connect"
            android:layout_centerVertical="true"
            android:background="@drawable/phone"/>

        <ImageView 
            android:id="@+id/connect"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:background="@drawable/break1"/>

         <ImageView 
            android:id="@+id/break_image"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_toRightOf="@+id/connect"
            android:layout_centerVertical="true"
            android:background="@drawable/camera_break"
            />

    </RelativeLayout>

    <LinearLayout
        android:id="@+id/Reconnect_button_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_below="@+id/layout_break_text"
        android:layout_centerInParent="true"
        android:orientation="horizontal" >


        <ImageButton
            android:id="@+id/Imgbtn_reconnect"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_weight="1"
            android:background="#00000000"
            android:src="@drawable/reconnect" />


    </LinearLayout>

    <FrameLayout
        android:id="@+id/player_frame"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">

       <FrameLayout
            android:id="@+id/player_surface_frame"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:layout_gravity="center" >

            <SurfaceView
                android:id="@+id/player_surface"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:layout_gravity="center" />

        </FrameLayout>
    </FrameLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:orientation="vertical" >

        <RelativeLayout
            android:id="@+id/top_buttonlayout"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:background="#444444" >

            <ImageView 
                android:id="@+id/imageBackground"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentLeft="true"
                android:background="@drawable/logo"
                />


            <ImageButton
                android:id="@+id/SettingButton"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_centerInParent="true"
                android:scaleType="fitXY"
                android:background="@drawable/parmeter_setting" />



            <ImageButton
                android:id="@+id/FileSavebutton"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentRight="true"
                android:scaleType="fitXY"
                android:background="@drawable/save_in_camera" />
    </LinearLayout>

</RelativeLayout>

在致电reconnect_fragment();时，它会在java.lang.NullPointerException显示reconnect_layout.setVisibility(View.VISIBLE);

有没有错？

如何解决这个问题？

Answer 1

正如您在评论中所述，framelayout是片段布局

所以改为

 reconnect_layout = (FrameLayout) view.findViewById(R.id.reconnect_layout);

如果它在活动xml中，则使用getActivity().findViewById

Answer 2

替换

reconnect_layout = (FrameLayout) getActivity().findViewById(R.id.reconnect_layout);

与

reconnect_layout = (FrameLayout) view.findViewById(R.id.reconnect_layout);

它在android中将framelayout设置为VISIBLE时显示java.lang.NullPointerException

2 个答案: