android - findViewById() 返回 null - 我该怎么办？

Question

我在我的 android 项目中使用 bottomSheetBehavior。请参阅以下代码:

在线游戏.java:

 // get the bottom sheet view
        ConstraintLayout llBottomSheet = findViewById(R.id.end_of_online_game_bottom_sheet_behavior_cl);

// init the bottom sheet behavior
        end_of_online_game_popup = BottomSheetBehavior.from(llBottomSheet);

avtivity_online_game.xml:

.
.
.

    <android.support.design.widget.CoordinatorLayout 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.androidsample.BottomSheetActivity">

        <!-- include bottom sheet -->
        <include
            android:id="@+id/includeBottomSheetBehavior"
            layout="@layout/test_end_of_online_game_popup" />

    </android.support.design.widget.CoordinatorLayout>
.
.
.

test_end_of_online_game_popup.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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/end_of_online_game_bottom_sheet_behavior_cl"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/cardview_light_background"
    android:visibility="gone"
    app:behavior_hideable="false"
    app:behavior_peekHeight="120dp"
    app:layout_behavior="android.support.design.widget.BottomSheetBehavior">
    .
    .
    .

问题是这一行:

ConstraintLayout llBottomSheet = findViewById(R.id.end_of_online_game_bottom_sheet_behavior_cl);

返回 null。我什至将代码位置更改为onResume，但它没有用。当我在 test_end_of_online_game_popup 中获得另一个元素时，它运行良好并且不为空。

问题是什么？

发送

Answer 1

两种选择:

1. ConstraintLayout llBottomSheet = findViewById(R.id. includeBottomSheetBehavior);

2. <include layout="@layout/test_end_of_online_game_popup" />