java - android findViewById 在 LinearLayout 中为 null

Question

android findViewById方法返回值为null

此 View 是自定义类

View .xml

<include
        android:id="@+id/view_before_login"
        layout="@layout/view_mypage_before_login"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

查看 Activity java( fragment )

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

        mBefore = (MemberBeforeLoginView)rootView.findViewById(R.id.view_before_login);
        mAfter = (MemberAfterLoginView)rootView.findViewById(R.id.view_after_login);

        mBefore.SetStateListener(this);
        mAfter.SetStateListener(this);

        route();

        return rootView;
    }

里面的xml是view_mypage_before_login.xml

<?xml version="1.0" encoding="utf-8"?>
<com.main.view.MemberAfterLoginView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ImageButton
        android:id="@+id/profile"
        android:layout_width="137dp"
        android:layout_height="121dp"
        app:srcCompat="@drawable/empty" />

    <Button
        android:id="@+id/logout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="logout" />
</com.main.view.MemberAfterLoginView>

com.main.view.MemberAfterLoginView.java

public class MemberAfterLoginView extends LinearLayout implements View.OnClickListener, MemberViewListener.MemberChildViewInterface {
    private MemberViewListener mMemberListener = null;

    private Button mBtnLogout = null;

    public MemberAfterLoginView(Context context) {
        super(context);
        initialize(context);
    }

    public MemberAfterLoginView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        initialize(context);
    }

    public MemberAfterLoginView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initialize(context);
    }

    private void initialize(Context context) {
        /*LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View v = inflater.inflate(R.layout.view_mypage_after_login, null);
        */

        mBtnLogout = (Button) findViewById(R.id.logout);
    }
...

为什么变量 mBtnLogout 为空？ (初始化函数内部变量)

我的英语还不成熟。抱歉。

Answer 1

private View initialize(Context context) {
    LayoutInflater inflater = (LayoutInflater) context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View v = inflater.inflate(R.layout.view_mypage_after_login, null);

    mBtnLogout = (Button) v.findViewById(R.id.logout);
    return v;
}

该按钮是新的膨胀 View 的一部分。因为 inflate 结果尚未应用于 Activity，但 activity.findViewById 找不到它。