使用ArrayAdapter填充ListView，应用程序停止

Question

大家好我是新手到android编程。我想通过数组适配器填充ListView。运行后错误是：不幸的是应用程序停止。我不知道什么是错的。我试着运行代码没有setAdapter和它工作正常。这里是我的代码

布局文件：1。 activity_main.xml中

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
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=".MainActivity" 
android:orientation="vertical"> 


<LinearLayout 
    android:orientation="horizontal" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"> 

     <EditText android:id="@+id/emp_name" 
     android:layout_weight="1" 
     android:layout_width="0dp" 
     android:layout_height="wrap_content" 
     android:hint="@string/emp_name" /> 

     <Button 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:text="@string/button_search" 
      android:clickable="true" 
      android:onClick="search" /> 
    </LinearLayout> 

<ListView 
    android:id="@+id/emp_list" 
    android:layout_width="75dp" 
    android:layout_height="fill_parent" > 
</ListView> 

</LinearLayout> 

2.emp_list_item.xml

<?xml version="1.0" encoding="utf-8"?> 
<TextView xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/emp_item" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" > 
</TextView> 

1. Main_activity.java

   protected void onCreate(Bundle savedInstanceState){ 
   
       super.onCreate(savedInstanceState); 
   
       String[] employees = {"Christophe Coenraets", "John Smith"}; 
   
       ListAdapter adapter = new ArrayAdapter<String> (this,R.layout.activity_main,R.id.emp_item,employees);  
   
       ListView employeeList = (ListView) findViewById(R.id.emp_list); 
       employeeList.setAdapter(adapter); 
       setContentView(R.layout.activity_main); 
   
   } 
   

Answer 1

您需要首先设置内容视图，如以下代码所示。

protected void onCreate(Bundle savedInstanceState){ 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    String[] employees = {"Christophe Coenraets", "John Smith"}; 

    ListAdapter adapter = new ArrayAdapter(this,R.layout.activity_main,R.id.emp_item,employees); 

    ListView employeeList = (ListView) findViewById(R.id.emp_list); 
    employeeList.setAdapter(adapter); 
} 

在你的情况下，它在findViewById（R.id.emp_list）上返回null，因为它的内容视图还没有被指定。

Answer 2

的setContentView必须首先使用...

protected void onCreate(Bundle savedInstanceState){ 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
String[] employees = {"Christophe Coenraets", "John Smith"}; 

ListAdapter adapter = new ArrayAdapter(this,R.layout.activity_main,R.id.emp_item,employees); 

ListView employeeList = (ListView) findViewById(R.id.emp_list); 
employeeList.setAdapter(adapter); 
}