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Java JSON数据不显示，而是显示空白屏幕

java android json

Java JSON数据不显示，而是显示空白屏幕,java,android,json,Java,Android,Json,尝试制作一个简单的应用程序，从服务器获取JSON数据并在自定义列表中显示它们，非常简单 但当我运行应用程序时，它会显示白色的空白屏幕，但没有数据。它也没有显示任何错误，我想如果有任何错误，它不会在我的手机上运行。但不显示获取的数据 这是main活动类 package com.example.root.employeedata; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import an

尝试制作一个简单的应用程序，从服务器获取JSON数据并在自定义列表中显示它们，非常简单

但当我运行应用程序时，它会显示白色的空白屏幕，但没有数据。它也没有显示任何错误，我想如果有任何错误，它不会在我的手机上运行。但不显示获取的数据

这是
main活动
类

package com.example.root.employeedata;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;

import org.json.JSONArray;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    List list  = new ArrayList<String>();
    String[] employees = new String[list.size()];
    String data = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        try{
            URL url = new URL("http://anontech.info/courses/cse491/employees.json");
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while(line != null){
                line = bufferedReader.readLine();
                data = data + line;
            }

            JSONArray array = new JSONArray(data);
            for(int i=0; i<array.length(); i++){
                String employeeName = array.getJSONObject(i).getString("name");
                list.add(employeeName);
            }

            for(int i=0; i<employees.length; i++){
                employees[i] = list.get(i).toString();
            }
        }
        catch (Exception e){
            e.printStackTrace();
        }

        for(int i=0; i<employees.length; i++){
            System.out.println(employees[i]);
        }

        ListView listView = (ListView) findViewById(R.id.listView);
        CustomAdapter customAdapter = new CustomAdapter();
        listView.setAdapter(customAdapter);
    }

    class CustomAdapter extends BaseAdapter{

        @Override
        public int getCount() {
            return employees.length;
        }

        @Override
        public Object getItem(int i) {
            return null;
        }

        @Override
        public long getItemId(int i) {
            return 0;
        }

        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            view = getLayoutInflater().inflate(R.layout.customlayout,null);

            TextView textView = (TextView)view.findViewById(R.id.employeeName);
            textView.setText(employees[i]);

            return view;
        }
    }
}
这是自定义列表的
customlayout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <TextView
        android:id="@+id/employeeName"
        android:layout_width="wrap_content"
        android:layout_height="69dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_weight="1"
        android:text="TextView" />

</RelativeLayout>
这是运行应用程序时显示的内容

我发现的其他问题与我的问题不匹配，否则将不会添加此问题。

这是因为您的employees字符串数组大小为0

List list  = new ArrayList<String>();//initially it has 0 size 
String[] employees = new String[list.size()];//list.size()==0

List List=new ArrayList（）//最初它的大小为0
String[]employees=新字符串[list.size（）]//list.size（）==0
将employees字符串[]转换为Arraylist将解决您的问题

ArrayList<String> employees = new ArrayList<String>();

ArrayList employees=new ArrayList（）；
细节 看到这段代码了吗

            for(int i=0; i<employees.length; i++){
                employees[i] = list.get(i).toString();
            }

for（int i=0；i您正在
主线程上执行网络请求。您可能会收到异常，但它被catch块屏蔽了


 catch (Exception e){
            e.printStackTrace();
        }


您需要使用进行网络请求

类似于以下内容。创建一个内部类：


private class GetJsonTask extends AsyncTask<URL, Void, String> {
     protected String doInBackground(URL... urls) {
         try{
            HttpURLConnection httpURLConnection = (HttpURLConnection) urls[0].openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while(line != null){
                line = bufferedReader.readLine();
                data = data + line;
            }
            return data;

        }
        catch (Exception e){
            e.printStackTrace();

        }
        return null;
     }



     protected void onPostExecute(String result) {
         if(result!=null){
         JSONArray array = new JSONArray(result);
            for(int i=0; i<array.length(); i++){
                String employeeName = array.getJSONObject(i).getString("name");
                list.add(employeeName);
            }
         }
     }
 }



私有类GetJsonTask扩展异步任务{
受保护的字符串doInBackground（URL…URL）{
试一试{
HttpURLConnection HttpURLConnection=（HttpURLConnection）URL[0]。openConnection（）；
InputStream InputStream=httpURLConnection.getInputStream（）；
BufferedReader BufferedReader=新的BufferedReader（新的InputStreamReader（inputStream））；
字符串行=”；
while（行！=null）{
line=bufferedReader.readLine（）；
数据=数据+行；
}
返回数据；
}
捕获（例外e）{
e、 printStackTrace（）；
}
返回null；
}
受保护的void onPostExecute（字符串结果）{
如果（结果！=null）{
JSONArray数组=新的JSONArray（结果）；

对于（inti=0；i1）-确保您的服务器连接逻辑远离UI线程，您可以使用以下内容

4-使用而不是
ListView
或至少使用
ViewHolder
模式

5-完整示例


import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;

import org.json.JSONArray;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final ListView listView = (ListView) findViewById(R.id.listView);
        // Make server logic inside Async Task.
        new AsyncTaskHandler(new OnFinishCallback() {
            @Override
            public void onSuccess(List<String> result) {
                CustomAdapter customAdapter = new CustomAdapter(result);
                listView.setAdapter(customAdapter);
            }
        }).execute("http://anontech.info/courses/cse491/employees.json");
    }

    class CustomAdapter extends BaseAdapter {

        private final List<String> employees;

        public CustomAdapter(List<String> result) {
            this.employees = result;
        }

        @Override
        public int getCount() {
            return employees.size();
        }

        @Override
        public String getItem(int position) {
            return employees.get(position);
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        // Use ViewHolder pattern.
        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            final ViewHolder viewHolder;
            if (view !=null){
                viewHolder = (ViewHolder) view.getTag();
            }else {
                view = getLayoutInflater().inflate(R.layout.customlayout, null);
                viewHolder = new ViewHolder();
                viewHolder.textView = (TextView) view.findViewById(R.id.employeeName);
                view.setTag(viewHolder);
            }
            viewHolder.textView.setText(getItem(i));
            return view;
        }


        // Should use View Holder pattern
        public class ViewHolder{
            TextView textView;
        }
    }


    /**
     * Static inner class to handle memory leak with inner class.
     */
    public static class AsyncTaskHandler extends AsyncTask<String, Void, List<String>> {
        private final OnFinishCallback callback;
        public AsyncTaskHandler(OnFinishCallback callback) {
            this.callback = callback;
        }

        @Override
        protected List<String> doInBackground(String... args) {
            List<String> result = new ArrayList<>();
            try {
                URL url = new URL(args[0]);
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line = "";
                String data = "";
                while (line != null) {
                    line = bufferedReader.readLine();
                    data = data + line;
                }

                JSONArray array = new JSONArray(data);
                for (int i = 0; i < array.length(); i++) {
                    String employeeName = array.getJSONObject(i).getString("name");
                    result.add(employeeName);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            return result;
        }

        @Override
        protected void onPostExecute(List<String> result) {
            callback.onSuccess(result);
        }
    }

    public interface OnFinishCallback{
        void onSuccess(List<String> result);
    }
}



导入android.os.AsyncTask；
导入android.support.v7.app.AppActivity；
导入android.os.Bundle；
导入android.util.Log；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.BaseAdapter；
导入android.widget.ListView；
导入android.widget.TextView；
导入org.json.JSONArray；
导入java.io.BufferedReader；
导入java.io.InputStream；
导入java.io.InputStreamReader；
导入java.net.HttpURLConnection；
导入java.net.URL；
导入java.util.ArrayList；
导入java.util.List；
公共类MainActivity扩展了AppCompatActivity{
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.activity_main）；
最终ListView ListView=（ListView）findViewById（R.id.ListView）；
//在异步任务中创建服务器逻辑。
新的AsyncTaskHandler（新的OnFinishCallback（）{
@凌驾
成功时公开作废（列表结果）{
CustomAdapter CustomAdapter=新的CustomAdapter（结果）；
setAdapter（customAdapter）；
}
}).执行（”http://anontech.info/courses/cse491/employees.json");
}
类CustomAdapter扩展了BaseAdapter{
私人最终雇员名单；
公共CustomAdapter（列表结果）{
这就是结果；
}
@凌驾
public int getCount（）{
return employees.size（）；
}
@凌驾
公共字符串getItem（int位置）{
返回员工。获取（职位）；
}
@凌驾
公共长getItemId（int位置）{
返回0；
}
//使用ViewHolder图案。
@凌驾
公共视图getView（int i、视图视图、视图组视图组）{
最终持票人；
如果（视图！=null）{
viewHolder=（viewHolder）view.getTag（）；
}否则{
view=GetLayoutFlater（）.充气（R.layout.customlayout，null）；
viewHolder=新的viewHolder（）；
viewHolder.textView=（textView）view.findViewById（R.id.employeeName）；
view.setTag（viewHolder）；
}
viewHolder.textView.setText（getItem（i））；
返回视图；
}
//应该使用视图保持器模式
公共类视图持有者{
文本视图文本视图；
}
}
/**
*使用内部类处理内存泄漏的静态内部类。
*/
公共静态类AsyncTaskHandler扩展了AsyncTask{
私有最终回调；
公共AsyncTaskHandler（OnFinishCallback回调）{
this.callback=回调；
}
@凌驾
受保护列表doInBackground（字符串…参数）{
列表结果=新建ArrayList（）；
试一试{
URL=新URL（参数[0]）；
HttpURLConnection HttpURLConnection=（HttpURLConnection）url.openConnection（）；
InputStream InputStream=httpURLConnection.getInputStream（）；
BufferedReader BufferedReader=新的BufferedReader（新的InputStreamReader（inputStream））；
字符串行=”；
字符串数据=”；
while（行！=null）{
line=bufferedReader.readLine（）；
数据=数据+行；
}
JSONArray数组=新的JSONArray（数据）；
对于（int i=0；iprivate class GetJsonTask extends AsyncTask<URL, Void, String> {
     protected String doInBackground(URL... urls) {
         try{
            HttpURLConnection httpURLConnection = (HttpURLConnection) urls[0].openConnection();
            InputStream inputStream = httpURLConnection.getInputStream();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String line = "";
            while(line != null){
                line = bufferedReader.readLine();
                data = data + line;
            }
            return data;

        }
        catch (Exception e){
            e.printStackTrace();

        }
        return null;
     }



     protected void onPostExecute(String result) {
         if(result!=null){
         JSONArray array = new JSONArray(result);
            for(int i=0; i<array.length(); i++){
                String employeeName = array.getJSONObject(i).getString("name");
                list.add(employeeName);
            }
         }
     }
 }



// Make server logic inside Async Task.
    new AsyncTaskHandler(new OnFinishCallback() {
        @Override
        public void onSuccess(List<String> result) {
            CustomAdapter customAdapter = new CustomAdapter(result);
            listView.setAdapter(customAdapter);
        }
    }).execute("http://anontech.info/courses/cse491/employees.json");



/**
 * Static inner class to handle memory leak with inner class.
 */
public static class AsyncTaskHandler extends AsyncTask<String, Void, List<String>> {
    private final OnFinishCallback callback;
    public AsyncTaskHandler(OnFinishCallback callback) {
        this.callback = callback;
    }
.....
}



        @Override
        protected void onPostExecute(List<String> result) {
            // Executed under UI thread to update UI component.
            callback.onSuccess(result); 
        }



        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            final ViewHolder viewHolder;
        .....
        }



import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;

import org.json.JSONArray;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final ListView listView = (ListView) findViewById(R.id.listView);
        // Make server logic inside Async Task.
        new AsyncTaskHandler(new OnFinishCallback() {
            @Override
            public void onSuccess(List<String> result) {
                CustomAdapter customAdapter = new CustomAdapter(result);
                listView.setAdapter(customAdapter);
            }
        }).execute("http://anontech.info/courses/cse491/employees.json");
    }

    class CustomAdapter extends BaseAdapter {

        private final List<String> employees;

        public CustomAdapter(List<String> result) {
            this.employees = result;
        }

        @Override
        public int getCount() {
            return employees.size();
        }

        @Override
        public String getItem(int position) {
            return employees.get(position);
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        // Use ViewHolder pattern.
        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            final ViewHolder viewHolder;
            if (view !=null){
                viewHolder = (ViewHolder) view.getTag();
            }else {
                view = getLayoutInflater().inflate(R.layout.customlayout, null);
                viewHolder = new ViewHolder();
                viewHolder.textView = (TextView) view.findViewById(R.id.employeeName);
                view.setTag(viewHolder);
            }
            viewHolder.textView.setText(getItem(i));
            return view;
        }


        // Should use View Holder pattern
        public class ViewHolder{
            TextView textView;
        }
    }


    /**
     * Static inner class to handle memory leak with inner class.
     */
    public static class AsyncTaskHandler extends AsyncTask<String, Void, List<String>> {
        private final OnFinishCallback callback;
        public AsyncTaskHandler(OnFinishCallback callback) {
            this.callback = callback;
        }

        @Override
        protected List<String> doInBackground(String... args) {
            List<String> result = new ArrayList<>();
            try {
                URL url = new URL(args[0]);
                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                InputStream inputStream = httpURLConnection.getInputStream();
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                String line = "";
                String data = "";
                while (line != null) {
                    line = bufferedReader.readLine();
                    data = data + line;
                }

                JSONArray array = new JSONArray(data);
                for (int i = 0; i < array.length(); i++) {
                    String employeeName = array.getJSONObject(i).getString("name");
                    result.add(employeeName);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            return result;
        }

        @Override
        protected void onPostExecute(List<String> result) {
            callback.onSuccess(result);
        }
    }

    public interface OnFinishCallback{
        void onSuccess(List<String> result);
    }
}