안녕하세요 저는 Android 앱 개발을 배우고 있습니다. 이를 위해 간단한 배경 화면 앱을 만들고 싶었습니다. 따라서 여기에 제시된 내용을 대략적으로 썼습니다. json에서 배경 화면 URL을 얻고 싶습니다. 안타깝게도 서버에서 데이터를 가져올 수 없습니다. java.lang.NullPointerException: Attempt to read from null array
jsonParse asynctask에서 데이터를 올바르게 가져 오는 방법은 무엇입니까? 나는 이것에 하루 종일 붙어 있습니다. 여기서 무엇이 잘못되었을 수 있습니까? 내 코드는 다음과 같습니다.
myjson.json :
{
"walls":[
{"ourUrl":"http://www.hdbloggers.net/wp-content/uploads/2016/01/Wallpapers-for-Android.jpg"},
{"ourUrl":"http://androidwallpape.rs/content/02-wallpapers/131-night-sky/wallpaper-2707591.jpg"},
{"ourUrl":"http://androidwallpape.rs/content/02-wallpapers/155-starrynight/starry-night-sky-star-galaxy-space-dark-9-wallpaper.jpg"}
]
}
MainActivity.java :
package regalstreak.me.wallpapers;
import android.app.Activity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
public class MainActivity extends Activity {
RecyclerView recyclerView;
RecyclerView.LayoutManager layoutManager;
RecyclerView.Adapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView)findViewById(R.id.recycler_view);
layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
adapter = new RecyclerAdapter(this);
recyclerView.setAdapter(adapter);
}
}
RecyclerAdapter.java :
package regalstreak.me.wallpapers;
import android.content.Context;
import android.os.AsyncTask;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import org.apache.commons.io.IOUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.List;
// This is a recycleradapter which will set the correct images to the correct position in the recyclerview.
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
private Context myCtx1;
String[] arr;
String[] arrurl;
String jsonURL = "http://dev.regalstreak.me/myjson.json";
public RecyclerAdapter(Context ctx) {
this.myCtx1 = ctx;
}
public ImageView Image;
private String[] mText = {
"Text 1",
"Text 2",
"Text 3"
};
public class ViewHolder extends RecyclerView.ViewHolder {
public TextView Text;
public ViewHolder(View itemView) {
super(itemView);
Image = (ImageView) itemView.findViewById(R.id.image_view);
Text = (TextView) itemView.findViewById(R.id.text_view);
}
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
View v = LayoutInflater.from(viewGroup.getContext())
.inflate(R.layout.wallpapers_list, viewGroup, false);
ViewHolder viewHolder = new ViewHolder(v);
return viewHolder;
}
@Override
public void onBindViewHolder(ViewHolder viewHolder, int i) {
viewHolder.Text.setText(mText[i]);
new jsonParse().execute();
new DownloadImageTask(Image).execute(arrurl[i]);
}
@Override
public int getItemCount() {
return mText.length;
}
class jsonParse extends AsyncTask<String, Void, String[]> {
protected String[] doInBackground(String[] urls) {
String myText = null;
String url = urls[0];
String ourUrl;
try {
InputStream in = new java.net.URL(jsonURL).openStream();
myText = IOUtils.toString(in, "utf-8");
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
// Parse the json
List<String> allUrls = new ArrayList<String>();
JSONObject jsonObjectRoot = new JSONObject(myText);
JSONArray jsonArray = jsonObjectRoot.getJSONArray("walls");
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
ourUrl = jsonObject.getString("ourUrl");
allUrls.add(ourUrl);
}
arr = allUrls.toArray(new String[allUrls.size()]);
} catch (JSONException e) {
e.printStackTrace();
}
return arr;
}
protected void onPostExecute(String[] result){
arrurl = result;
}
}
}
DownloadImageTask.java :
package regalstreak.me.wallpapers;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.ImageView;
import java.io.InputStream;
// Here, we will download the wallpapers obtained from jsonData with an asynctask.
public class DownloadImageTask extends AsyncTask<String, Void, Bitmap>{
ImageView bmImage;
public DownloadImageTask(ImageView bmImage){
this.bmImage = bmImage;
}
protected Bitmap doInBackground(String... urls) {
String urldisplay = urls[0];
Bitmap mIcon11 = null;
try {
InputStream in = new java.net.URL(urldisplay).openStream();
mIcon11 = BitmapFactory.decodeStream(in);
in.close();
} catch (Exception e) {
Log.e("Error getting images.", e.getMessage());
e.printStackTrace();
}
return mIcon11;
}
protected void onPostExecute(Bitmap result){
bmImage.setImageBitmap(result);
}
}
activity_main.xml :
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="regalstreak.me.wallpapers.MainActivity">
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/recycler_view" />
</RelativeLayout>
wallpaper_list.xml :
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/relative"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="5dp">
<ImageView
android:id="@+id/image_view"
android:layout_width="match_parent"
android:layout_height="150dp" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignBottom="@id/image_view"
android:alpha="0.6"
android:background="@color/colorDivider"
android:padding="9dp">
<TextView
android:id="@+id/text_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAlignment="center"
android:textColor="@color/colorPrimaryText" />
</RelativeLayout>
</RelativeLayout>
빠른 응답과 캐시와 같은 기능을 위해 여기에서 HttpURLConnection 클래스를 사용했습니다. URL에서 수신 된 데이터는 입력 스트림에 추가되고 JSON 클래스와 함께 사용할 수있는 문자열 객체를 얻기 위해 문자열 빌더로 변환됩니다.
추신-AsyncTask 코드를 MainActivity 자체에 추가하고이를 위해 별도의 Java 파일을 만들지 마십시오.
팁-항상이 도구를 사용하여 json 확인-jsonlint.com
MainActivity
/*
your code
*/
@Override
protected void onCreate(Bundle savedInstanceState) {
new MyAsyncTask().execute("");
}
class MyAsyncTask extends AsyncTask<String, String, Void> {
private ProgressDialog progressDialog = new ProgressDialog(StartScreen.this);
InputStream inputStream = null;
String result = "";
ArrayList<String> list;
protected void onPreExecute() {
progressDialog.setTitle("Downloading JSON Data");
progressDialog.show();
// above code makes a dialog with a progress bar
}
@Override
protected Void doInBackground(String... params) {
ArrayList<String> param = new ArrayList<String>();
URL url, url2;
try{
url = new URL("http://dev.regalstreak.me/myjson.json");
// link to your json file
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setUseCaches(false);
inputStream = new BufferedInputStream(urlConnection.getInputStream());
}catch (MalformedURLException malle){
Log.e("Mal", ""+malle);
malle.printStackTrace();
}catch (IOException ioe){
Log.e("IO", ""+ioe);
ioe.printStackTrace();
}
// Convert response to string using String Builder
try {
BufferedReader bReader = new BufferedReader(new InputStreamReader(inputStream, "utf-8"), 8);
StringBuilder sBuilder = new StringBuilder();
String line = null;
while ((line = bReader.readLine()) != null) {
sBuilder.append(line + "\n");
}
inputStream.close();
result = sBuilder.toString();
} catch (Exception e) {
Log.e("StringBuilding", "Error converting result " + e.toString());
}
return null;
}
protected void onPostExecute(Void v) {
//parse JSON data
try {
JSONObject jobj = new JSONObject(result);
//Taking a JSON Array from the JSONObject created above
String url = jobj.getString("ourUrl");
// We are adding this string to the ArrayList
list.add(url);
progressDialog.dismiss();
Context con = ListLoader.this.getApplication();
adapter = new RecyclerAdapter(list,con);
recyclerView.setAdapter(adapter);
} catch (JSONException e) {
Log.e("JSONException", "Error: " + e.toString());
} // catch (JSONException e)
}
}
/*
your code
*/
이제 목록에 이미지를 더 효과적으로 표시하려면 repo Universal 이미지 로더를 사용하십시오. 그것은 많은 기능을 가지고 있습니다. 여기에서 얻을 수 있습니다-https: //github.com/nostra13/Android-Universal-Image-Loader
그런 다음 이러한 종류의 코드를 추가하여 이미지를 표시합니다. onBindViewHolder 안에 넣으십시오.
어댑터
@Override
public void onBindViewHolder(DataHolder holder, int position) {
ImageLoaderConfiguration config;
config = new ImageLoaderConfiguration.Builder(mContext).build();
ImageLoader.getInstance().init(config);
imageLoader = ImageLoader.getInstance();
DisplayImageOptions options = new DisplayImageOptions.Builder()
.showImageForEmptyUri(R.drawable.ic_error_black_48dp) // displays this image not found
.showImageOnFail(R.drawable.ic_error_black_48dp) // Displays this on failure
.showImageOnLoading(R.drawable.white) // Displays while loading
.cacheInMemory(false)
.cacheOnDisk(true)
.build();
imageLoader.displayImage(list.get(position), holder.imageView, options);
// We are feeding the urls here.
}
이 기사는 인터넷에서 수집됩니다. 재 인쇄 할 때 출처를 알려주십시오.
침해가 발생한 경우 연락 주시기 바랍니다[email protected] 삭제
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