使用URL中的Json數組填充Android listview

Question

我正在為一個學校項目開發此應用程序。 該應用程序的基本原理是使用Volley從URL檢索json數組，然后使用該數組來填充listview。 聽起來很簡單，但由於我是應用程序開發的新手，這讓我感到最頭痛。 因此，經過無數的教程和無數的錯誤之后，我設法解決了所有問題。 但是現在當我運行該應用程序時，我得到的只是一個空白屏幕。 我的日志沒有顯示任何錯誤。

Log:
10-27 18:49:39.662 1997-1997/com.example.sahan.volley2 I/art: Not late-    
enabling -Xcheck:jni (already on)
10-27 18:49:39.964 1997-2018/com.example.sahan.volley2        
D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
10-27 18:49:39.967 1997-1997/com.example.sahan.volley2 D/:             
HostConnection::get() New Host Connection established 0xa5432140, tid   
1997
10-27 18:49:39.979 1997-1997/com.example.sahan.volley2 D/Atlas:   
Validating map...
10-27 18:49:40.156 1997-2018/com.example.sahan.volley2   
I/OpenGLRenderer: Initialized EGL, version 1.4
10-27 18:49:40.210 1997-2018/com.example.sahan.volley2 
D/OpenGLRenderer: Enabling debug mode 0
10-27 18:49:40.243 1997-2018/com.example.sahan.volley2 W/EGL_emulation:   
eglSurfaceAttrib not implemented
10-27 18:49:40.243 1997-2018/com.example.sahan.volley2    
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 
0xa5480b60, error=EGL_SUCCESS
10-27 18:49:40.696 1997-2018/com.example.sahan.volley2 W/EGL_emulation: 
eglSurfaceAttrib not implemented
10-27 18:49:40.696 1997-2018/com.example.sahan.volley2   
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface   
0xa5480b80, error=EGL_SUCCESS
10-27 18:49:40.718 1997-1997/com.example.sahan.volley2 I/Choreographer:   
Skipped 43 frames!  The application may be doing too much work on its    
main thread.
10-27 18:49:40.932 1997-1997/com.example.sahan.volley2 D/Volley: [1]   
2.onErrorResponse: MainActivity

***** MainActivity.java ******

package com.example.sahan.volley2;

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar; 
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;

import com.example.sahan.volley2.Adapter.CustomListAdapter;
import com.example.sahan.volley2.app.AppController;
import com.example.sahan.volley2.Model.lot;

import java.util.ArrayList;
import java.util.List;

import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.ListView;

import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonArrayRequest;

public class MainActivity extends Activity {
// Log tag
private static final String TAG = MainActivity.class.getSimpleName();

//json url
private static final String url =       
"http://localhost/smartpark/get_info.php";
private ProgressDialog pDialog;
private List<lot> lotList = new ArrayList<lot>();
private ListView listView;
private CustomListAdapter adapter;

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

listView = (ListView) findViewById(R.id.list);
adapter = new CustomListAdapter(this, lotList);
listView.setAdapter(adapter);

pDialog = new ProgressDialog(this);
// Showing progress dialog before making http request
pDialog.setMessage("Loading...");
pDialog.show();

// changing action bar color
//  getActionBar().setBackgroundDrawable(
//        new ColorDrawable(Color.parseColor("#1b1b1b")));

// Creating volley request obj
JsonArrayRequest movieReq = new JsonArrayRequest(url,
        new Response.Listener<JSONArray>() {
            @Override
            public void onResponse(JSONArray response) {
                Log.d(TAG, response.toString());
                hidePDialog();

                // Parsing json
                for (int i = 0; i < response.length(); i++) {
                    try {

                        JSONObject obj = response.getJSONObject(i);
                        lot lot = new lot();
                        lot.setLot(obj.getString("lot"));
                        lot.setSpaces(obj.getString("spaces"));
                        lot.setRates(obj.getString("rates"));

                        // adding movie to movies array
                        lotList.add(lot);

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

                }

                // notifying list adapter about data changes
                // so that it renders the list view with updated data
                adapter.notifyDataSetChanged();
            }
        }, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        VolleyLog.d(TAG, "Error: " + error.getMessage());
        hidePDialog();

    }
});

// Adding request to request queue
AppController.getInstance().addToRequestQueue(movieReq);
}

@Override
public void onDestroy() {
super.onDestroy();
hidePDialog();
}

private void hidePDialog() {
if (pDialog != null) {
    pDialog.dismiss();
    pDialog = null;
}
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}

}

****** CustomListAdapter ******

package com.example.sahan.volley2.Adapter;

/**
* Created by Sahan on 2015-10-27.
*/
import com.example.sahan.volley2.R;
import com.example.sahan.volley2.app.AppController;
import com.example.sahan.volley2.Model.lot;

import java.util.List;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.NetworkImageView;

public class CustomListAdapter extends BaseAdapter {
private Activity activity;
private LayoutInflater inflater;
private List<lot> lotItems;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();

public CustomListAdapter(Activity activity, List<lot> lotItems) {
this.activity = activity;
this.lotItems = lotItems;
}

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

@Override
public Object getItem(int location) {
return lotItems.get(location);
}

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

@Override
public View getView(int position, View convertView, ViewGroup parent) {

if (inflater == null)
    inflater = (LayoutInflater) activity
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (convertView == null)
    convertView = inflater.inflate(R.layout.list_row, null);

if (imageLoader == null)
    imageLoader = AppController.getInstance().getImageLoader();
TextView lot = (TextView) convertView.findViewById(R.id.lot);
TextView spaces = (TextView) convertView.findViewById(R.id.spaces);
TextView rates = (TextView) convertView.findViewById(R.id.rates);

// getting movie data for the row
lot m = lotItems.get(position);

// title
lot.setText(m.getLot());

// rating
spaces.setText("Spaces: " + String.valueOf(m.getSpaces()));


// release year
rates.setText(String.valueOf(m.getRates()));

return convertView;
}
}

**** AppController.java ****

package com.example.sahan.volley2.app;

/**
* Created by Sahan on 2015-10-27.
*/
import com.example.sahan.volley2.utils.LruBitmapCache;
import android.app.Application;
import android.text.TextUtils;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.Volley;

public class AppController extends Application {

public static final String TAG = AppController.class
    .getSimpleName();

private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;

private static AppController mInstance;

@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}

public static synchronized AppController getInstance() {
return mInstance;
}

public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
    mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}

return mRequestQueue;
}

public ImageLoader getImageLoader() {
getRequestQueue();
if (mImageLoader == null) {
    mImageLoader = new ImageLoader(this.mRequestQueue,
            new LruBitmapCache());
}
return this.mImageLoader;
}

public <T> void addToRequestQueue(Request<T> req, String tag) {
// set the default tag if tag is empty
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}

public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}

public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
    mRequestQueue.cancelAll(tag);
}
}
}

**** lot.java ****

package com.example.sahan.volley2.app;

/**
* Created by Sahan on 2015-10-27.
*/
import com.example.sahan.volley2.utils.LruBitmapCache;
import android.app.Application;
import android.text.TextUtils;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.Volley;

public class AppController extends Application {

public static final String TAG = AppController.class
    .getSimpleName();

private RequestQueue mRequestQueue;
private ImageLoader mImageLoader;

private static AppController mInstance;

@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}

public static synchronized AppController getInstance() {
return mInstance;
}

public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
    mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}

return mRequestQueue;
}

public ImageLoader getImageLoader() {
getRequestQueue();
if (mImageLoader == null) {
    mImageLoader = new ImageLoader(this.mRequestQueue,
            new LruBitmapCache());
}
return this.mImageLoader;
}

public <T> void addToRequestQueue(Request<T> req, String tag) {
// set the default tag if tag is empty
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}

public <T> void addToRequestQueue(Request<T> req) {
req.setTag(TAG);
getRequestQueue().add(req);
}

public void cancelPendingRequests(Object tag) {
if (mRequestQueue != null) {
    mRequestQueue.cancelAll(tag);
}
}
} 

**** LruBitmapCache ****

package com.example.sahan.volley2.utils;

/**
* Created by Sahan on 2015-10-27.
*/
import com.android.volley.toolbox.ImageLoader.ImageCache;

import android.graphics.Bitmap;
import android.support.v4.util.LruCache;

public class LruBitmapCache extends LruCache<String, Bitmap> implements
ImageCache {
public static int getDefaultLruCacheSize() {
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
final int cacheSize = maxMemory / 8;

return cacheSize;
}

public LruBitmapCache() {
this(getDefaultLruCacheSize());
}

public LruBitmapCache(int sizeInKiloBytes) {
super(sizeInKiloBytes);
}

@Override
protected int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight() / 1024;
}

 @Override
 public Bitmap getBitmap(String url) {
return get(url);
}

@Override
public void putBitmap(String url, Bitmap bitmap) {
put(url, bitmap);
}
}

**** AndroidManifest.xml ****

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.sahan.volley2" >

<uses-permission android:name="android.permission.INTERNET" />

<application
android:name="com.example.sahan.volley2.app.AppController"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme" >

<activity
    android:name=".MainActivity"
    android:label="@string/app_name"
    android:theme="@style/AppTheme.NoActionBar" >
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>
</application>

**** 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"
xmlns:app="http://schemas.android.com/apk/res-auto" 
android:layout_width="match_parent"
android:layout_height="match_parent" 
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/activity_main" tools:context=".MainActivity">

<ListView
android:id="@+id/list"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:divider="@color/list_divider"
android:dividerHeight="1dp"
android:listSelector="@drawable/list_row_selector" />

**** list_row.xml ****

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="@drawable/list_row_selector"
android:padding="8dp" >


<!-- Lot Title -->
<TextView
android:id="@+id/lot"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="@dimen/lot"
android:textStyle="bold" />

<!-- Rating -->
<TextView
android:id="@+id/spaces"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@id/lot"
android:layout_marginTop="1dip"
android:textSize="@dimen/spaces" />

<!-- Genre -->
<TextView
android:id="@+id/rates"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="@id/spaces"
android:layout_marginTop="5dp"
android:textColor="@color/rates"
android:textSize="@dimen/rates" />

**** build.gradle ****

apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "23.0.1"

defaultConfig {
applicationId "com.example.sahan.volley2"
minSdkVersion 15
targetSdkVersion 23
versionCode 1
versionName "1.0"
multiDexEnabled true
}
buildTypes {
release {
    minifyEnabled false
    proguardFiles getDefaultProguardFile('proguard-android.txt'),       'proguard-rules.pro'
}
}
}

dependencies {
//compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:23.0.1'
compile 'com.android.support:design:23.0.1'
compile 'com.mcxiaoke.volley:library-aar:1.0.0'
}

Answer 1

由於某種原因，看來Lot.java與AppController.java相同。 您的Lot類應如下所示：

public class Lot {
    private String mString;
    private String mSpaces;
    private String mRates;

    public Lot() {
    }

    public String getString() {
        return mString;
    }

    public void setString(String string) {
        mString = string;
    }

    public String getSpaces() {
        return mSpaces;
    }

    public void setSpaces(String spaces) {
        mSpaces = spaces;
    }

    public String getRates() {
        return mRates;
    }

    public void setDirector(String rates) {
        mRates = rates;
    }

}

Lot類是您要在MainActivity的內部存儲的節點/項目

private List<Lot> lotList = new ArrayList<Lot>();