Question

我一直试图让我的列表视图工作很长一段时间，我只是将我的监听器从onClick更改为onItemClick以更好地处理listview项目但应用程序再次崩溃，我的代码如下，任何帮助将不胜感激。

类别：

public class ListViewAdapterProduct extends BaseAdapter {

Context mContext;
ListView listView = (ListView) findViewById(R.id.listview1);  

listView.setOnItemClickListener(new OnItemClickListener() { 

    @Override
    public void onItemClick(AdapterView<?> parent, View v, int position, long id){

        Resources res = mContext.getResources();
        productTitleArray = res.getStringArray(R.array.titles_product);

        for (String productTitle : productTitleArray) 
        {
            if(productTitle.equals("productOne")) 
            {
            Log.d("Msg", "Found");
            }               
        else
            {
                Log.d("Msg", "Not Found");
            }
        }
    }
});

我以前的帖子：

Compare XML String From Java Class When Item In ListView Is Clicked

logcat的：

03-30 16:40:39.027: E/AndroidRuntime(811): FATAL EXCEPTION: main
03-30 16:40:39.027: E/AndroidRuntime(811): java.lang.NullPointerException
03-30 16:40:39.027: E/AndroidRuntime(811):  at com.twostarii.test.ListViewAdapterproduct.getView(ListViewAdapterproduct.java:91)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.AbsListView.obtainView(AbsListView.java:2159)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.ListView.makeAndAddView(ListView.java:1831)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.ListView.fillDown(ListView.java:674)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.ListView.fillFromTop(ListView.java:735)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.ListView.layoutChildren(ListView.java:1652)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.AbsListView.onLayout(AbsListView.java:1994)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.View.layout(View.java:14008)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewGroup.layout(ViewGroup.java:4373)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1021)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.View.layout(View.java:14008)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewGroup.layout(ViewGroup.java:4373)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.View.layout(View.java:14008)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewGroup.layout(ViewGroup.java:4373)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1663)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1521)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.View.layout(View.java:14008)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewGroup.layout(ViewGroup.java:4373)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.View.layout(View.java:14008)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewGroup.layout(ViewGroup.java:4373)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1892)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1711)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:989)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4351)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.Choreographer.doCallbacks(Choreographer.java:562)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.Choreographer.doFrame(Choreographer.java:532)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.os.Handler.handleCallback(Handler.java:725)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.os.Handler.dispatchMessage(Handler.java:92)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.os.Looper.loop(Looper.java:137)
03-30 16:40:39.027: E/AndroidRuntime(811):  at android.app.ActivityThread.main(ActivityThread.java:5041)
03-30 16:40:39.027: E/AndroidRuntime(811):  at java.lang.reflect.Method.invokeNative(Native Method)
03-30 16:40:39.027: E/AndroidRuntime(811):  at java.lang.reflect.Method.invoke(Method.java:511)
03-30 16:40:39.027: E/AndroidRuntime(811):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-30 16:40:39.027: E/AndroidRuntime(811):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-30 16:40:39.027: E/AndroidRuntime(811):  at dalvik.system.NativeStart.main(Native Method)

的活动：

public class MainActivityproduct extends MainActivity {


ListView list;
ListViewAdapterproduct adapter;
EditText editsearch;
String[] position;
String[] productTitles;
String[] productDescriptions;
int[] images={
        R.drawable.list_product_one, 
        R.drawable.list_product_two, 
        R.drawable.list_product_three,
    };


ArrayList<ClassproductList> arraylist = new ArrayList<ClassproductList>();

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

    position = new String[] { "1", "2", "3"};

    Resources res = getResources();
    productTitles = res.getStringArray(R.array.titles_product);
    productDescriptions = res.getStringArray(R.array.descriptions_product);

    list = (ListView) findViewById(R.id.listview1);

    list.setAdapter(adapter);

    for (int i = 0; i < position.length; i++)
    {
        ClassproductList wp = new ClassproductList(productTitles[i], productDescriptions[i],images[i]);
        arraylist.add(wp);
    }

    adapter = new ListViewAdapterproduct(this, arraylist);

    list.setAdapter(adapter);

    editsearch = (EditText) findViewById(R.id.search);

    editsearch.addTextChangedListener(new TextWatcher() {

        @Override
       public void afterTextChanged(Editable arg0) {
            String text = editsearch.getText().toString().toLowerCase(Locale.getDefault());
            adapter.filter(text);
        }

        @Override
        public void beforeTextChanged(CharSequence arg0, int arg1,
                int arg2, int arg3) {
        }

        public void onTextChanged(CharSequence arg0, int arg1, int arg2,
                int arg3) {
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

Answer 1

Context mContext;中的问题为空

在您的活动集mContext = this;中，因此mContext将是您将能够使用资源的活动context

这是正确的代码：

因为您已经在适配器中发送了this，所以需要在那里捕获它

public class ListViewAdapterProduct extends BaseAdapter {

Context mContext;
ArrayList<ClassproductList> arraylist;

ListView listView = (ListView) findViewById(R.id.listview1);  

 //add this
public ListViewAdapterProduct (Context mContext,ArrayList<ClassproductList> arraylist)
{
this.mContext = mContext;

this.arraylist = arraylist;
}

Answer 2

您已声明了mContext，但尚未对其进行初始化。

您可以在适配器的构造函数中执行此操作：

public class ListViewAdapterProduct extends BaseAdapter {

    Context mContext;

    // the construcor that initializes the context
    public ListViewAdapterProduct(Context c){
        mContext = c;
    }
    ...

但是，您发布的跟踪信息表明问题出在您的适配器的getView（）方法第91行。您也应该检查一下。

ListViewAdapterproduct.getView(ListViewAdapterproduct.java:91)

编辑：

list.setAdapter(adapter);

在这一行中，适配器为null，你没有初始化它...（你设置适配器两次，首先是null）。在本地定义变量是一种很好的做法，只有在实际需要时才使它们成为类变量。这样就很难忘记初始化。

Answer 3

已解决!!!

我从onItemClick（复杂地使用自定义适配器）改为onClick（简单地使用自定义适配器）并应用：

view.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View arg0) {

    String mytitle=holder.title.getText().toString();

    if(mytitle.equals("ProductOne")){
        Intent intent1 = new Intent(mContext, ProductClass.ProductOne);
        mContext.startActivity(intent1);

        ...        

    }
}

不得不补充：

String mytitle=holder.title.getText().toString();

ListView项OnItemClick在ListView适配器类中崩溃

3 个答案: