Android布局文件使用<include>标签出现NullPointerException问题

出现问题

在布局文件中使用标签大家肯定都不陌生，能减少冗余的代码。之前写项目中也一直在用到，但是有一次用的时候直接出现了NullPointerException的问题，下面是出现问题的代码

Activity中的代码

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    TextView textView = (TextView) findViewById(R.id.text_include);

    RelativeLayout rl_include = (RelativeLayout) findViewById(R.id.rl_layout);
    rl_include.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Toast.makeText(MainActivity.this, "text", Toast.LENGTH_SHORT).show();
        }
    });

}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.administrator.mytestapp.MainActivity">

    	<include
   	     android:id="@+id/include"
    		layout="@layout/layout_inclue" />
    
    	<TextView
		    android:id="@+id/textView"
		    android:layout_width="wrap_content"
		    android:layout_height="wrap_content"
		    android:layout_centerHorizontal="true"
		    android:layout_marginTop="135dp"
		    android:text="Hello World!" />
</RelativeLayout>

layout_inclue.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
	android:id="@+id/rl_layout"
	android:layout_width="match_parent"
	android:layout_height="45dp"
	android:background="@android:color/darker_gray"
	android:orientation="vertical">

    <TextView
    	android:id="@+id/text_include"
    	android:layout_width="wrap_content"
    	android:layout_height="wrap_content"
    	android:layout_centerInParent="true"
    	android:text="INCLUDE_TITLE"
    	android:textColor="@android:color/holo_red_dark" />

</RelativeLayout>

出错的地方

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.RelativeLayout.setOnClickListener(android.view.View$OnClickListener)' on a null object reference

是在设置layout_inclue布局中相对布局点击事件出现空指针的问题,最后是发现是activity_main.xml中标签的id覆盖了layout_inclue.xml中根布局的id，导致的在Activity中获取layout_inclue.xml根布局的为null。

提供两个解决方法

1.删除activity_main.xml中标签的id，程序即可正常运行

2.使用activity_main.xml中标签的id

 RelativeLayout rl_include = (RelativeLayout) findViewById(R.id.include);
    rl_include.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Toast.makeText(MainActivity.this, "text", Toast.LENGTH_SHORT).show();
        }
    });