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我正在尝试使用以下代码使用字符串数组中的值填充一个简单的列表视图，它会引发一个空指针异常。该列表是从上一个统计这个的活动中获取的，并且该列表是有效的我已经检查它包含字符串价值观

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Bundle extras = getIntent().getExtras(); 
        final ListView listview = (ListView) findViewById(R.id.listview);
        List<Map<String, String>> deptList = new ArrayList<Map<String,String>>();

        if (extras != null) {

            deplist = extras.getStringArray("deparments");
            Log.w("Got","List");

            }
         ArrayAdapter<String> adapter = new ArrayAdapter<String>(Home.this,
                  android.R.layout.simple_list_item_1, android.R.id.text1, deplist);
         listview.setAdapter(adapter); 


        setContentView(R.layout.home);

这是堆栈跟踪

10-06 02:39:33.002: D/dalvikvm(1409): GC_FOR_ALLOC freed 59K, 7% free 2541K/2720K, paused 139ms, total 141ms
10-06 02:39:33.102: I/dalvikvm-heap(1409): Grow heap (frag case) to 4.058MB for 1536016-byte allocation
10-06 02:39:33.152: D/dalvikvm(1409): GC_FOR_ALLOC freed <1K, 5% free 4041K/4224K, paused 48ms, total 48ms
10-06 02:39:33.642: D/gralloc_goldfish(1409): Emulator without GPU emulation detected.
10-06 02:39:35.952: W/Got(1409): List
10-06 02:39:36.092: D/AndroidRuntime(1409): Shutting down VM
10-06 02:39:36.092: W/dalvikvm(1409): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
10-06 02:39:36.372: E/AndroidRuntime(1409): FATAL EXCEPTION: main
10-06 02:39:36.372: E/AndroidRuntime(1409): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.usa/com.example.usa.Home}: java.lang.NullPointerException
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.os.Looper.loop(Looper.java:137)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.ActivityThread.main(ActivityThread.java:5103)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at java.lang.reflect.Method.invokeNative(Native Method)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at java.lang.reflect.Method.invoke(Method.java:525)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at dalvik.system.NativeStart.main(Native Method)
10-06 02:39:36.372: E/AndroidRuntime(1409): Caused by: java.lang.NullPointerException
10-06 02:39:36.372: E/AndroidRuntime(1409):     at com.example.usa.Home.onCreate(Home.java:51)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.Activity.performCreate(Activity.java:5133)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
10-06 02:39:36.372: E/AndroidRuntime(1409):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
10-06 02:39:36.372: E/AndroidRuntime(1409):     ... 11 more
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1 回答 1

2

你在打电话

final ListView listview = (ListView) findViewById(R.id.listview);

前

setContentView(R.layout.home);

这没有任何意义。findViewById()在当前膨胀的视图中查找视图。但是你直到 10 行之后才用setContentView(). 放在setContentView()开头onCreate()。

于 2013-10-06T06:47:39.200 回答