Java Android、谷歌地图API、JSON问题。获取空指针异常
我正在开发一个小型的人事应用程序来帮助我学习Android开发和Java 让我先让大家知道谷歌地图部分正在应用程序中工作。当应用程序启动并获取手机的正确当前位置时，它正在加载 此外，我的JSON功能也能正常工作。数据是使用他们的API从www.wunderground.com中提取出来的，我的代码获取了我想要的内容，并创建了一个Arraylist，然后很好地填充它，并在应用程序中显示它 问题是，我正在尝试获取两段JSON数据，并创建一个google map Marker对象，并将其显示在地图上 下面是我的代码： 此方法使用从JsonData.java获取的JSON数据创建Cyclone对象，我将在下面展示 Cyclone.javaJava Android、谷歌地图API、JSON问题。获取空指针异常,java,android,json,google-maps,Java,Android,Json,Google Maps,我正在开发一个小型的人事应用程序来帮助我学习Android开发和Java 让我先让大家知道谷歌地图部分正在应用程序中工作。当应用程序启动并获取手机的正确当前位置时，它正在加载 此外，我的JSON功能也能正常工作。数据是使用他们的API从www.wunderground.com中提取出来的，我的代码获取了我想要的内容，并创建了一个Arraylist，然后很好地填充它，并在应用程序中显示它 问题是，我正在尝试获取两段JSON数据，并创建一个google map Marker对象，并将其显示在地图上
public class Cyclone {
// Category of the cyclone (e.g. -2, -1, 0, 1, 2, 3, 4, or 5)
private int category;
// Latitude & Longitude of Cyclone
private float latitude, longitude;
// Cyclone name
private String name;
// Cyclone heading (N, S, E, or W)
private String heading;
// Wind speed in Cyclone
private String windSpeedKnots;
// Url to website with Cyclone data
private String url;
/**
* CONSTRUCTOR
* Create a new Cyclone object.
*
* @param constCategory is the category of the cyclone (e.g. -2, -1, 0, 1, 2, 3, 4, or 5)
* @param constLatitude is the Latitude of the cyclone
* @param constLongitude is the Longitude of the cyclone
* @param constName is the name of the Cyclone
* @param constHeading is the direction the cyclone is moving
* @param constWindSpeedKnots is the speed of the wind the Cyclone is producing
* @param constUrl is the url of the website that is providing the data
*/
public Cyclone(int constCategory, float constLatitude, float constLongitude,String constName,
String constHeading, String constWindSpeedKnots, String constUrl) {
category = constCategory;
latitude = constLatitude;
longitude = constLongitude;
name = constName;
heading = constHeading;
windSpeedKnots = constWindSpeedKnots;
url = constUrl;
}
/**
* Setting public getters for the private variables above for use of other classes
*/
// Get the storm category
public int getCategory() {
return category;
}
// Get the cyclones Latitude
public float getLatitude() {
return latitude;
}
//Get the cyclones Longitude
public float getLongitude() {
return longitude;
}
// Get the cyclones name
public String getName() {
return name;
}
// Get the cyclones heading
public String getHeading() {
return heading;
}
// Get the cyclones wind speed
public String getWindSpeedKnots() {
return windSpeedKnots;
}
// Get the Url
public String getUrl() {
return url;
}
/**
* Return a list of {@link Cyclone} objects that has been built up from
* parsing a JSON response.
*/
public static ArrayList<Cyclone> extractFeatureFromJson(String cycloneJSON) {
// Create an empty ArrayList to start adding Cyclones to
ArrayList<Cyclone> cyclones = new ArrayList<>();
// Try to parse the cycloneJSON response string. If there's a problem with the way the JSON
// is formatted, a JSONException exception object will be thrown.
// Catch the exception , and print the error message to the logs.
try {
JSONObject rootJsonObject = new JSONObject(cycloneJSON);
// Create JSONArray associated with the key called "currenthurricane", which represents
// a list of cyclones from JSON response.
JSONArray currentHurricaneArray = rootJsonObject.getJSONArray("currenthurricane");
/**
* Loop through each section in the currentHurricaneArray array & create an
* {@link Cyclone} object for each one
*
*/
for (int i = 0; i < currentHurricaneArray.length(); i++) {
//Get cyclone JSONObject at position i in the array
JSONObject cycloneProperties = currentHurricaneArray.getJSONObject(i);
// Extract "stormInfo" object
JSONObject stormInfo = cycloneProperties.optJSONObject("stormInfo");
//Extract “stormName_Nice” & "requesturl" for Cyclone's name and url
String name = stormInfo.optString("stormName_Nice");
String url = stormInfo.optString("wuiurl");
// Extract "Current" object
JSONObject current = cycloneProperties.optJSONObject("Current");
// Extract "SaffirSimpsonCategory" key
int category = current.optInt("SaffirSimpsonCategory");
//Extract "Lat" & "Lon" keys to get cyclone position
float latitude = (float) current.optDouble("lat");
float longitude = (float) current.optDouble("lon");
//Extract "WindSpeed" object
JSONObject windSpeed = current.optJSONObject("WindSpeed");
//Extract wind speed in "Knots" Key
int Kts = windSpeed.optInt("Kts");
String knots = Kts + " Knots";
//Extract "Movement" object
JSONObject movement = current.optJSONObject("Movement");
//Extract movement direction in "Text" key
String direction = movement.optString("Text");
Cyclone cyclone = new Cyclone(category, latitude, longitude, name, direction, knots, url);
//Add new cyclone to list
cyclones.add(cyclone);
}
public class MainActivity extends AppCompatActivity implements
LoaderManager.LoaderCallbacks<List<Cyclone>>,
OnMapReadyCallback,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener,
LocationListener {
....
//Creating a Cyclone object, calling it from Cyclone.java
Cyclone trackedCyclone = null;
//getting the three bits of info I need/want (Name, lat, lon)
String name = trackedCyclone.getName();
float lat = trackedCyclone.getLatitude();
float lon = trackedCyclone.getLongitude();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.cyclone_list);
....
// Obtain the SupportMapFragment and get notified when the map is ready
//Calling up the map fragment from cyclone_list.xml
MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.google_map);
mapFragment.getMapAsync(this);
....
@Override
public void onMapReady(GoogleMap mapLocalInstance) {
//Setting mapReady to true
mapReady = true;
//displaying cyclone map marker on the map
LatLng cycloneMarker = new LatLng(lat, lon);
googleMap.addMarker(new MarkerOptions().position(cycloneMarker).title(name));
//Loading local instance map from Callback
googleMap = mapLocalInstance;
googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
//checks for permission using the Support library before enabling the My Location layer
//Initialize Google Play Services
if (android.os.Build.VERSION.SDK_INT >= M) {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
buildGoogleApiClient();
googleMap.setMyLocationEnabled(true);
}
} else {
buildGoogleApiClient();
googleMap.setMyLocationEnabled(true);
}
}
public class Cyclone {
// Category of the cyclone (e.g. -2, -1, 0, 1, 2, 3, 4, or 5)
private int category;
// Latitude & Longitude of Cyclone
private float latitude, longitude;
// Cyclone name
private String name;
// Cyclone heading (N, S, E, or W)
private String heading;
// Wind speed in Cyclone
private String windSpeedKnots;
// Url to website with Cyclone data
private String url;
/**
* CONSTRUCTOR
* Create a new Cyclone object.
*
* @param constCategory is the category of the cyclone (e.g. -2, -1, 0, 1, 2, 3, 4, or 5)
* @param constLatitude is the Latitude of the cyclone
* @param constLongitude is the Longitude of the cyclone
* @param constName is the name of the Cyclone
* @param constHeading is the direction the cyclone is moving
* @param constWindSpeedKnots is the speed of the wind the Cyclone is producing
* @param constUrl is the url of the website that is providing the data
*/
public Cyclone(int constCategory, float constLatitude, float constLongitude,String constName,
String constHeading, String constWindSpeedKnots, String constUrl) {
category = constCategory;
latitude = constLatitude;
longitude = constLongitude;
name = constName;
heading = constHeading;
windSpeedKnots = constWindSpeedKnots;
url = constUrl;
}
/**
* Setting public getters for the private variables above for use of other classes
*/
// Get the storm category
public int getCategory() {
return category;
}
// Get the cyclones Latitude
public float getLatitude() {
return latitude;
}
//Get the cyclones Longitude
public float getLongitude() {
return longitude;
}
// Get the cyclones name
public String getName() {
return name;
}
// Get the cyclones heading
public String getHeading() {
return heading;
}
// Get the cyclones wind speed
public String getWindSpeedKnots() {
return windSpeedKnots;
}
// Get the Url
public String getUrl() {
return url;
}
/**
* Return a list of {@link Cyclone} objects that has been built up from
* parsing a JSON response.
*/
public static ArrayList<Cyclone> extractFeatureFromJson(String cycloneJSON) {
// Create an empty ArrayList to start adding Cyclones to
ArrayList<Cyclone> cyclones = new ArrayList<>();
// Try to parse the cycloneJSON response string. If there's a problem with the way the JSON
// is formatted, a JSONException exception object will be thrown.
// Catch the exception , and print the error message to the logs.
try {
JSONObject rootJsonObject = new JSONObject(cycloneJSON);
// Create JSONArray associated with the key called "currenthurricane", which represents
// a list of cyclones from JSON response.
JSONArray currentHurricaneArray = rootJsonObject.getJSONArray("currenthurricane");
/**
* Loop through each section in the currentHurricaneArray array & create an
* {@link Cyclone} object for each one
*
*/
for (int i = 0; i < currentHurricaneArray.length(); i++) {
//Get cyclone JSONObject at position i in the array
JSONObject cycloneProperties = currentHurricaneArray.getJSONObject(i);
// Extract "stormInfo" object
JSONObject stormInfo = cycloneProperties.optJSONObject("stormInfo");
//Extract “stormName_Nice” & "requesturl" for Cyclone's name and url
String name = stormInfo.optString("stormName_Nice");
String url = stormInfo.optString("wuiurl");
// Extract "Current" object
JSONObject current = cycloneProperties.optJSONObject("Current");
// Extract "SaffirSimpsonCategory" key
int category = current.optInt("SaffirSimpsonCategory");
//Extract "Lat" & "Lon" keys to get cyclone position
float latitude = (float) current.optDouble("lat");
float longitude = (float) current.optDouble("lon");
//Extract "WindSpeed" object
JSONObject windSpeed = current.optJSONObject("WindSpeed");
//Extract wind speed in "Knots" Key
int Kts = windSpeed.optInt("Kts");
String knots = Kts + " Knots";
//Extract "Movement" object
JSONObject movement = current.optJSONObject("Movement");
//Extract movement direction in "Text" key
String direction = movement.optString("Text");
Cyclone cyclone = new Cyclone(category, latitude, longitude, name, direction, knots, url);
//Add new cyclone to list
cyclones.add(cyclone);
}
public class MainActivity extends AppCompatActivity implements
LoaderManager.LoaderCallbacks<List<Cyclone>>,
OnMapReadyCallback,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener,
LocationListener {
....
//Creating a Cyclone object, calling it from Cyclone.java
Cyclone trackedCyclone = null;
//getting the three bits of info I need/want (Name, lat, lon)
String name = trackedCyclone.getName();
float lat = trackedCyclone.getLatitude();
float lon = trackedCyclone.getLongitude();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.cyclone_list);
....
// Obtain the SupportMapFragment and get notified when the map is ready
//Calling up the map fragment from cyclone_list.xml
MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.google_map);
mapFragment.getMapAsync(this);
....
@Override
public void onMapReady(GoogleMap mapLocalInstance) {
//Setting mapReady to true
mapReady = true;
//displaying cyclone map marker on the map
LatLng cycloneMarker = new LatLng(lat, lon);
googleMap.addMarker(new MarkerOptions().position(cycloneMarker).title(name));
//Loading local instance map from Callback
googleMap = mapLocalInstance;
googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
//checks for permission using the Support library before enabling the My Location layer
//Initialize Google Play Services
if (android.os.Build.VERSION.SDK_INT >= M) {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
buildGoogleApiClient();
googleMap.setMyLocationEnabled(true);
}
} else {
buildGoogleApiClient();
googleMap.setMyLocationEnabled(true);
}
}
/**
*返回从中建立的{@link Cyclone}对象列表
*解析JSON响应。
*/
公共静态ArrayList extractFeatureFromJson（字符串cycloneJSON）{
//创建一个空的ArrayList以开始向其添加旋风分离器
ArrayList旋风分离器=新ArrayList（）；
//尝试解析cycloneJSON响应字符串。如果JSON响应的方式有问题
//如果已格式化，将抛出JSONException异常对象。
//捕获异常，并将错误消息打印到日志中。
试一试{
JSONObject rootJsonObject=新的JSONObject（cycloneJSON）；
//创建与名为“currenthurricane”的键关联的JSONArray，该键表示
//JSON响应中的气旋列表。
JSONArray currentHurricaneArray=rootJsonObject.getJSONArray（“currenthurricane”）；
/**
*循环浏览currentHurricaneArray中的每个部分并创建一个
*{@link Cyclone}对象
*
*/
对于（int i=0；ipublic class Cyclone {
// Category of the cyclone (e.g. -2, -1, 0, 1, 2, 3, 4, or 5)
private int category;
// Latitude & Longitude of Cyclone
private float latitude, longitude;
// Cyclone name
private String name;
// Cyclone heading (N, S, E, or W)
private String heading;
// Wind speed in Cyclone
private String windSpeedKnots;
// Url to website with Cyclone data
private String url;
/**
* CONSTRUCTOR
* Create a new Cyclone object.
*
* @param constCategory is the category of the cyclone (e.g. -2, -1, 0, 1, 2, 3, 4, or 5)
* @param constLatitude is the Latitude of the cyclone
* @param constLongitude is the Longitude of the cyclone
* @param constName is the name of the Cyclone
* @param constHeading is the direction the cyclone is moving
* @param constWindSpeedKnots is the speed of the wind the Cyclone is producing
* @param constUrl is the url of the website that is providing the data
*/
public Cyclone(int constCategory, float constLatitude, float constLongitude,String constName,
String constHeading, String constWindSpeedKnots, String constUrl) {
category = constCategory;
latitude = constLatitude;
longitude = constLongitude;
name = constName;
heading = constHeading;
windSpeedKnots = constWindSpeedKnots;
url = constUrl;
}
/**
* Setting public getters for the private variables above for use of other classes
*/
// Get the storm category
public int getCategory() {
return category;
}
// Get the cyclones Latitude
public float getLatitude() {
return latitude;
}
//Get the cyclones Longitude
public float getLongitude() {
return longitude;
}
// Get the cyclones name
public String getName() {
return name;
}
// Get the cyclones heading
public String getHeading() {
return heading;
}
// Get the cyclones wind speed
public String getWindSpeedKnots() {
return windSpeedKnots;
}
// Get the Url
public String getUrl() {
return url;
}
/**
* Return a list of {@link Cyclone} objects that has been built up from
* parsing a JSON response.
*/
public static ArrayList<Cyclone> extractFeatureFromJson(String cycloneJSON) {
// Create an empty ArrayList to start adding Cyclones to
ArrayList<Cyclone> cyclones = new ArrayList<>();
// Try to parse the cycloneJSON response string. If there's a problem with the way the JSON
// is formatted, a JSONException exception object will be thrown.
// Catch the exception , and print the error message to the logs.
try {
JSONObject rootJsonObject = new JSONObject(cycloneJSON);
// Create JSONArray associated with the key called "currenthurricane", which represents
// a list of cyclones from JSON response.
JSONArray currentHurricaneArray = rootJsonObject.getJSONArray("currenthurricane");
/**
* Loop through each section in the currentHurricaneArray array & create an
* {@link Cyclone} object for each one
*
*/
for (int i = 0; i < currentHurricaneArray.length(); i++) {
//Get cyclone JSONObject at position i in the array
JSONObject cycloneProperties = currentHurricaneArray.getJSONObject(i);
// Extract "stormInfo" object
JSONObject stormInfo = cycloneProperties.optJSONObject("stormInfo");
//Extract “stormName_Nice” & "requesturl" for Cyclone's name and url
String name = stormInfo.optString("stormName_Nice");
String url = stormInfo.optString("wuiurl");
// Extract "Current" object
JSONObject current = cycloneProperties.optJSONObject("Current");
// Extract "SaffirSimpsonCategory" key
int category = current.optInt("SaffirSimpsonCategory");
//Extract "Lat" & "Lon" keys to get cyclone position
float latitude = (float) current.optDouble("lat");
float longitude = (float) current.optDouble("lon");
//Extract "WindSpeed" object
JSONObject windSpeed = current.optJSONObject("WindSpeed");
//Extract wind speed in "Knots" Key
int Kts = windSpeed.optInt("Kts");
String knots = Kts + " Knots";
//Extract "Movement" object
JSONObject movement = current.optJSONObject("Movement");
//Extract movement direction in "Text" key
String direction = movement.optString("Text");
Cyclone cyclone = new Cyclone(category, latitude, longitude, name, direction, knots, url);
//Add new cyclone to list
cyclones.add(cyclone);
}
public class MainActivity extends AppCompatActivity implements
LoaderManager.LoaderCallbacks<List<Cyclone>>,
OnMapReadyCallback,
GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener,
LocationListener {
....
//Creating a Cyclone object, calling it from Cyclone.java
Cyclone trackedCyclone = null;
//getting the three bits of info I need/want (Name, lat, lon)
String name = trackedCyclone.getName();
float lat = trackedCyclone.getLatitude();
float lon = trackedCyclone.getLongitude();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.cyclone_list);
....
// Obtain the SupportMapFragment and get notified when the map is ready
//Calling up the map fragment from cyclone_list.xml
MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.google_map);
mapFragment.getMapAsync(this);
....
@Override
public void onMapReady(GoogleMap mapLocalInstance) {
//Setting mapReady to true
mapReady = true;
//displaying cyclone map marker on the map
LatLng cycloneMarker = new LatLng(lat, lon);
googleMap.addMarker(new MarkerOptions().position(cycloneMarker).title(name));
//Loading local instance map from Callback
googleMap = mapLocalInstance;
googleMap.setMapType(GoogleMap.MAP_TYPE_SATELLITE);
//checks for permission using the Support library before enabling the My Location layer
//Initialize Google Play Services
if (android.os.Build.VERSION.SDK_INT >= M) {
if (ContextCompat.checkSelfPermission(this,
Manifest.permission.ACCESS_FINE_LOCATION)
== PackageManager.PERMISSION_GRANTED) {
buildGoogleApiClient();
googleMap.setMyLocationEnabled(true);
}
} else {
buildGoogleApiClient();
googleMap.setMyLocationEnabled(true);
}
}
public类MainActivity扩展了AppCompatActivity实现
LoaderManager.LoaderCallbacks，
四月一日，
GoogleAppClient.ConnectionCallbacks，
GoogleAppClient.OnConnectionFailedListener，
位置侦听器{
....
//创建Cyclone对象，从Cyclone.java调用它
Cyclone trackedCyclone=null；
//获取我需要/想要的三位信息（姓名、纬度、经度）
字符串名称=trackedCyclone.getName（）；
float lat=trackedCyclone.getLatitude（）；
float lon=trackedconclone.getLongitude（）；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（R.layout.cyclone_列表）；
....
//获取SupportMapFragment，并在地图准备就绪时获得通知
//从cyclone_list.xml调用映射片段
MapFragment MapFragment=（MapFragment）getFragmentManager（）；
getMapAsync（这个）；
....
@凌驾
Mapready上的公共无效（谷歌地图本地化）{
//将mapReady设置为true
mapredy=true；
//在地图上显示气旋地图标记
LatLng cycloneMarker=新的LatLng（lat，lon）；
addMarker（新的MarkerOptions（）.position（cycloneMarker.title（name））；
//从回调加载本地实例映射
googleMap=MapLocationInstance；
googleMap.setMapType（googleMap.MAP类型卫星）；
//在启用“我的位置”层之前，使用支持库检查权限
//初始化Google Play服务
if（android.os.Build.VERSION.SDK_INT>=M）{
如果（ContextCompat.checkSelfPermission）（此，
清单.权限.访问（位置）
==PackageManager.权限（已授予）{
buildGoogleAppClient（）；
googleMap.setMyLocationEnabled（true）；
}
}否则{
buildGoogleAppClient（）；
googleMap.setMyLocationEnabled（true）；
}
}