Question

    private List<Product> itemList;

    public List<Product> getItemList() {
        return itemList;
    }

然后尝试接受这样......

 public void doMySearch (String query){
    System.out.println("bikaMiden");
    List<Product> searchResult = new ArrayList<Product>();
    List<Product> result = new ArrayList<Product>();
    System.out.println("bikagamwwwwwwwww");
    result= adapter.getItemList();
    System.out.println("bikaMIA");
    for (Product product : result) {
        System.out.println("bika");
        if (product.getProductName().contains(query)) {

            searchResult.add(product);
            System.out.println("vrika" + product);
            }
        }

    adapter.setItemList(searchResult);
    adapter.notifyDataSetChanged();
}

我已经尝试了50种不同的aproach它总是在分配给结果命令时崩溃，如果你知道帮助我...

    02-27 21:51:58.847: D/AndroidRuntime(3194): Shutting down VM
02-27 21:51:58.857: W/dalvikvm(3194): threadid=1: thread exiting with uncaught exception (group=0x41465700)
02-27 21:51:58.897: E/AndroidRuntime(3194): FATAL EXCEPTION: main
02-27 21:51:58.897: E/AndroidRuntime(3194): java.lang.RuntimeException: Unable to start activity ComponentInfo{uk.ac.kent.jhp20.shopper/uk.ac.kent.jhp20.shopper.ProductListActivity}: java.lang.NullPointerException
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.os.Looper.loop(Looper.java:137)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.ActivityThread.main(ActivityThread.java:5103)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at java.lang.reflect.Method.invokeNative(Native Method)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at java.lang.reflect.Method.invoke(Method.java:525)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at dalvik.system.NativeStart.main(Native Method)
02-27 21:51:58.897: E/AndroidRuntime(3194): Caused by: java.lang.NullPointerException
02-27 21:51:58.897: E/AndroidRuntime(3194):     at uk.ac.kent.jhp20.shopper.ProductListActivity.doMySearch(ProductListActivity.java:139)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at uk.ac.kent.jhp20.shopper.ProductListActivity.onCreate(ProductListActivity.java:115)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.Activity.performCreate(Activity.java:5133)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-27 21:51:58.897: E/AndroidRuntime(3194):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
02-27 21:51:58.897: E/AndroidRuntime(3194):     ... 11 more
02-27 21:57:00.157: D/dalvikvm(3221): GC_FOR_ALLOC freed 49K, 8% free 2778K/2988K, paused 43ms, total 47ms
02-27 21:57:00.177: I/dalvikvm-heap(3221): Grow heap (frag case) to 3.939MB for 1127536-byte allocation
02-27 21:57:00.217: D/dalvikvm(3221): GC_FOR_ALLOC freed 2K, 6% free 3876K/4092K, paused 39ms, total 39ms
02-27 21:57:00.408: D/libEGL(3221): loaded /system/lib/egl/libEGL_emulation.so
02-27 21:57:00.418: D/(3221): HostConnection::get() New Host Connection established 0x2a1bdc30, tid 3221
02-27 21:57:00.437: D/libEGL(3221): loaded /system/lib/egl/libGLESv1_CM_emulation.so
02-27 21:57:00.448: D/libEGL(3221): loaded /system/lib/egl/libGLESv2_emulation.so
02-27 21:57:00.489: W/EGL_emulation(3221): eglSurfaceAttrib not implemented
02-27 21:57:00.489: D/OpenGLRenderer(3221): Enabling debug mode 0
02-27 21:57:00.538: D/dalvikvm(3221): GC_FOR_ALLOC freed 8K, 5% free 4259K/4444K, paused 27ms, total 27ms
02-27 21:57:00.627: D/dalvikvm(3221): GC_FOR_ALLOC freed 1K, 4% free 4614K/4796K, paused 20ms, total 20ms
02-27 21:57:00.707: D/dalvikvm(3221): GC_FOR_ALLOC freed <1K, 4% free 4969K/5148K, paused 21ms, total 22ms
02-27 21:57:00.797: I/Choreographer(3221): Skipped 30 frames!  The application may be doing too much work on its main thread.

这里是logcat ...请帮助..我正在构建一个Android项目，如果这个问题很愚蠢的话，我真的很新。更新适配器不为null我的oncreate方法在这里项目相当庞大所以我不得不选择一些部分......

private ProductListAdapter adapter;
private ListViewLoader loader;

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    //get the category form the intent
    Intent intent = getIntent();

    /*
     *  To here
     */
    adapter = new ProductListAdapter(this);
    setListAdapter(adapter);


    if(Intent.ACTION_SEARCH.equals(intent.getAction()))
    {
        String query = intent.getStringExtra(SearchManager.QUERY);
        System.out.println("bika");

        /*
         *  because you refer to it here
         */
        doMySearch(query);

        System.out.println("ti paixtike edw malakako?");
    }
    else
    {
        categoryId = intent.getIntExtra(MainActivity.SELECTED_CATEGORY, 1);

        /*
         *  Move this
         *
        adapter = new ProductListAdapter(this);
        setListAdapter(adapter);
         *
         */

        loader = new ListViewLoader(adapter, categoryId);
        loader.execute(String.format(MainActivity.WEBSERVER_GETLIST, categoryId));
    }

    setupActionBar();
}

Answer 1

适配器为null，因此无法调用getItemList（）！这会导致NullPointerException。

检查适配器是否为空。

Answer 2

很难看出你的null可能在哪里，但正如Edwin T已经指出它可能是适配器对象。但是我建议在这种情况下对适配器和项目结果进行空检查。

这样的事情：

public void doMySearch(String query){

    if (adapter != null) {
        List<Product> searchResult = new ArrayList<Product>();
        List<Product> result = new ArrayList<Product>();

        result = adapter.getItemList();

        if (result != null) {
            for (Product product : result) {

                if (product.getProductName().contains(query)) {

                    searchResult.add(product);
                }
            }

            adapter.setItemList(searchResult);
            adapter.notifyDataSetChanged();
        }
    }
}

如何将从方法中获得的arraylist分配到另一个arraylist？

2 个答案: