view.findViewById() returns 空

Question

我已经使用 FrameLayout 来显示叠加屏幕。在实例化 RelativeLayout 时，findViewById returns null。这是 xml 文件:

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">

<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        />
    <me.relex.circleindicator.CircleIndicator
        android:id="@+id/indicator"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:layout_marginBottom="48dp"
        android:layout_gravity="bottom"
        app:ci_drawable="@drawable/orange_radius"
        app:ci_drawable_unselected="@drawable/white_radius"/>

</RelativeLayout>

<!--Below is the transparent layout positioned at startup -->
<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#70000000"
    android:id="@+id/topLayout">

    <ImageView
        android:id="@+id/ivInstruction"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:paddingTop="25dp"
        android:layout_marginRight="15dp"
        android:clickable="false"
        android:paddingLeft="20dip"
        android:scaleType="center"
        android:src="@drawable/home" />

</RelativeLayout>

片段代码：

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        mView = getActivity().getLayoutInflater().inflate(R.layout.our_work_layout, null);

        topLayout = (RelativeLayout) mView.findViewById(R.id.topLayout);


   if (isFirstTime()) {
        topLayout.setVisibility(View.INVISIBLE);
    }

    ViewPager viewpager = (ViewPager) mView.findViewById(R.id.viewpager);
    //  mPager.setAdapter(mAdapter);

    ImageAdapter adapter = new ImageAdapter(act);
    viewpager.setAdapter(adapter);


    CircleIndicator indicator = (CircleIndicator) mView.findViewById(R.id.indicator);;
    indicator.setViewPager(viewpager);
    return mView;
}

private boolean isFirstTime()
{
    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getContext());
    boolean ranBefore = preferences.getBoolean("RanBefore", false);
    if (!ranBefore) {

        SharedPreferences.Editor editor = preferences.edit();
        editor.putBoolean("RanBefore", true);
        editor.commit();
        topLayout.setVisibility(View.VISIBLE);
        topLayout.setOnTouchListener(new View.OnTouchListener(){

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                topLayout.setVisibility(View.INVISIBLE);
                return false;
            }

        });


    }
    return ranBefore;

}

Answer 1

您的问题在这里：

ViewPager viewpager = (ViewPager) mView.findViewById(R.id.viewpager);

此布局中没有"viewpager"。您使用了 ID "pager"。

将此行更正为以下内容：

ViewPager viewpager = (ViewPager) mView.findViewById(R.id.pager);

view.findViewById() returns 空

view.findViewById() returns null

android

android-fragments

android-framelayout