我添加了一个“特色”寻呼机 View 作为我的 ListView 的标题。寻呼机 View 从一个单独的 url 接收数据，而不是从 ListView 接收数据，因此我正在发出两个单独的 Volley 请求。我已经在一个单独的项目中单独测试了寻呼机 View ，它可以完美地工作。 ListView 也可以在没有额外 Volley 请求的情况下完美运行。这是我的主要 Activity 。
public class MainActivity extends AppCompatActivity {
private ProgressDialog dialog=null ;
private CustomAdapter adapter;
private ListView list;
ArrayList<RowData> rowdata;
private SearchView searchView;
private MenuItem myActionMenuItem;
private ViewPager pageView;
private ArrayList<FeatureModel> fdata;
private FeatureAdapter featAdapt;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
LayoutInflater inflater = getLayoutInflater();
ViewGroup header = (ViewGroup) inflater.inflate(R.layout.feature_view, list,
false);
pageView = (ViewPager)findViewById(R.id.featuredView);
list=(ListView) findViewById(R.id.listView1);
list.addHeaderView(header);
list.setTextFilterEnabled(true);
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//Get item at position
RowData item = (RowData)parent.getItemAtPosition(position);
//Pass the image title and url to DetailsActivity
Intent intent = new Intent(MainActivity.this, DetailActivity.class);
intent.putExtra("title", item.getTitle());
intent.putExtra("image", item.getImageURL());
intent.putExtra("size", item.getProdSize());
intent.putExtra("date", item.getProdDate());
intent.putExtra("region", item.getRegionURL());
intent.putExtra("desc", item.getDetailURL());
//Start details activity
startActivity(intent);
}
});
rowdata=new ArrayList<RowData>();
dialog= new ProgressDialog(this, R.style.AppTheme);
dialog.setMessage("Loading...");
dialog.show();
JsonArrayRequest request = new JsonArrayRequest(url+url_file,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString()); try {
for(int i=0;i<response.length();i++){
String title=response.getJSONObject(i).getString("prod_name");
String size=response.getJSONObject(i).getString("prod_size");
String img_url;
String date = response.getJSONObject(i).getString("prod_date");
String detail_url = response.getJSONObject(i).getString("prod_desc");
String region_url = response.getJSONObject(i).getString("prod_region");
img_url = response.getJSONObject(i).getString("prod_image");
rowdata.add(new RowData(title, size, img_url,detail_url,region_url,date));
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
adapter=new CustomAdapter(MainActivity.this, rowdata);
list.setAdapter(adapter);
dialog.dismiss();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.d(TAG, "Error: " + error.getMessage());
dialog.dismiss();
}
});
VolleyController.getInstance().addToRequestQueue(request, tag_json_arry);
loadFeatures();
}
public void loadFeatures(){
JsonArrayRequest stringRequest = new JsonArrayRequest(FEAT_URL,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString()); try {
for(int i=0;i<response.length();i++){
String sid=response.getJSONObject(i).getString("fid");
String name=response.getJSONObject(i).getString("feat_name");
String img = response.getJSONObject(i).getString("feat_pic");
fdata.add(new FeatureModel(sid, name, img));
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
featAdapt=new FeatureAdapter(MainActivity.this, fdata);
pageView.setAdapter(featAdapt);
//dialog.dismiss();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.d(TAG, "Error: " + error.getMessage());
//dialog.dismiss();
}
});
VolleyController.getInstance().addToRequestQueue(stringRequest, TAG);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_main, menu);
myActionMenuItem = menu.findItem(R.id.action_search);
searchView = (SearchView) myActionMenuItem.getActionView();
searchView.clearFocus();
searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextSubmit(String query) {
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
Filter filter = adapter.getFilter();
if (TextUtils.isEmpty(newText)) {
filter.filter("");
} else {
filter.filter(newText);
}
return true;
}
});
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_search) {
return true;
}
if(id == R.id.action_info){
return true;
}
if(id == R.id.action_share){
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onResume() {
super.onResume();
}
@Override
protected void onPause() {
super.onPause();
}
}
这是 logcat:
Process: com.curtrostudios.prodarchive, PID: 7231 java.lang.NullPointerException at com.curtrostudios.prodarchive.MainActivity$4.onResponse(MainActivity.java:149) at com.curtrostudios.prodarchive.MainActivity$4.onResponse(MainActivity.java:140) at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:65) at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5072) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602) at dalvik.system.NativeStart.main(Native Method)
最佳答案
经过不断的研究和试错，我弄清楚了问题所在。问题不在于有两个 Volley 请求，而是 Volley 请求将 JSON 响应返回到空 View 。
最初的 pagerview 是这样的:
pageView = (ViewPager)findViewById(R.id.featuredView);
对于任何想要将 viewpager 作为 ListView 的 header 的人来说，这就是应该如何完成的。
标题 View 声明如下:
View header = (RelativeLayout)getLayoutInflater().inflate(R.layout.feature_view, null);
所以如果你想在那个布局中使用任何 View ，你必须声明
pageView = (ViewPager)header.findViewById(R.id.featuredView);
header.findViewById() 确保您从声明的 header 中找到 View 。
然后为了确保标题正确显示，我必须添加以下内容:
final DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
final int width = displayMetrics.widthPixels;
AbsListView.LayoutParams headerViewParams = new AbsListView.LayoutParams(width, 400);
header.setLayoutParams(headerViewParams);
这是您 Activity 的 onCreate() 方法中的完整代码:
//Use this to find the width of the device
final DisplayMetrics displayMetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
//This is where you declare the header layout
View header = (RelativeLayout)getLayoutInflater().inflate(R.layout.feature_view, null);
//This is where you find the view within the header layout
//that you're going to need or use
pageView = (ViewPager)header.findViewById(R.id.featuredView);
//This is where you set the layout params if the header layout
//isn't showing properly
AbsListView.LayoutParams headerViewParams = new AbsListView.LayoutParams(width, 400);
//Set the layout params for the header
header.setLayoutParams(headerViewParams);
list=(ListView)findViewById(R.id.listView1);
//add the header to the listview.
//in this case, ListView = list;
list.addHeaderView(header);
关于android - 在 Android 中的同一 Activity 中使用两个 Volley 请求时如何修复空指针异常？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37110901/