代码行未初始化导致nullpointerexecption

Question

我有一行代码,当我调试nullpointerexception时,我可以看到它是我的应用程序崩溃的原因.

导致nullpointer的代码行是这样的:

ListView storeList = (ListView) findViewById(R.id.storeList);

然后在调试模式下它尝试分配时崩溃:

storeList.setAdapter(arrayAdapter2);

我不知道为什么对象没有初始化.在ArrayAdapter它下面的初始化罚款.如果你

下面是实际的java活动文件:

public class StoreListView extends Activity {
UserFunctions userFunctions  = new UserFunctions();
ArrayAdapter<String> arrayAdapter2;
ArrayList<String> spinnerArray;



protected void onCreate(Bundle savedInstanceState) {
    ListView storeList = (ListView) findViewById(R.id.storeList);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.storelistviewpage);
    arrayAdapter2 = new ArrayAdapter<String>(StoreListView.this,android.R.layout.simple_list_item_1);
    spinnerArray = getIntent().getStringArrayListExtra("cusName");
    arrayAdapter2.addAll(spinnerArray);
    storeList.setAdapter(arrayAdapter2);
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main_screen, menu);
    return true;
}

}

下面是xml文件:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ListView
    android:id="@+id/storeList"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal|center_vertical" >

</ListView>

编辑:如果有人想知道我将活动添加到android mainfest

Answer 1

移动

ListView storeList = (ListView) findViewById(R.id.storeList);

setContentView()通话结束后.

由于当前的代码分配的结果findViewById() 之前 setContentView()被调用时,你会总是得到storeList是null,所以,你会得到一个NPE.