java如何从类中获取一个变量到主活动？

Question

在我的Android应用程序（Wheather应用程序）中，我有一个主要活动（在屏幕上显示wheater）和一个类（获取手机的当前位置）。 “Position”类获取纬度和经度，我希望将其发送到我的主要活动中以使用它们。为了做到这一点，我尝试使用getter，但这似乎不起作用。以下是两个类的代码：

位置类：（只需注意结尾的getter）

public class Position extends AppCompatActivity implements LocationListener {

private double longitude;
private double latitude;
private LocationManager locationManager;

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

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
            != PackageManager.PERMISSION_GRANTED &&
            ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
                    != PackageManager.PERMISSION_GRANTED) {

        return;
    }
    Location location = locationManager.getLastKnownLocation(locationManager.NETWORK_PROVIDER);

    onLocationChanged(location);


}

@Override
public void onLocationChanged(Location location) {
    longitude=location.getLongitude();
    latitude=location.getLatitude();

}

public double getLongitude1() {
    return this.longitude;
}

public double getLatitude1() {
    return this.latitude;
}

主要活动：（再次注意我试图使用经纬度的最后四行）

public class MainActivity extends AppCompatActivity {

TextView cityField, detailsField, currentTemperatureField, humidity_field, pressure_field, weatherIcon, updatedField;

Typeface weatherFont;

Position position = new Position();

private double latitude1;
private double longitude1;
private String latitude2;
private String longitude2;

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


    weatherFont = Typeface.createFromAsset(getApplicationContext().getAssets(), "fonts/weathericons-regular-webfont.ttf");

    cityField = (TextView)findViewById(R.id.city_field);
    updatedField = (TextView)findViewById(R.id.updated_field);
    detailsField = (TextView)findViewById(R.id.details_field);
    currentTemperatureField = (TextView)findViewById(R.id.current_temperature_field);
    humidity_field = (TextView)findViewById(R.id.humidity_field);
    pressure_field = (TextView)findViewById(R.id.pressure_field);
    weatherIcon = (TextView)findViewById(R.id.weather_icon);
    weatherIcon.setTypeface(weatherFont);


    Function.placeIdTask asyncTask =new Function.placeIdTask(new Function.AsyncResponse() {
        public void processFinish(String weather_city, String weather_description, String weather_temperature, String weather_humidity, String weather_pressure, String weather_updatedOn, String weather_iconText, String sun_rise) {

            cityField.setText(weather_city);
            updatedField.setText(weather_updatedOn);
            detailsField.setText(weather_description);
            currentTemperatureField.setText(weather_temperature);
            humidity_field.setText("Humidity: "+weather_humidity);
            pressure_field.setText("Pressure: "+weather_pressure);
            weatherIcon.setText(Html.fromHtml(weather_iconText));

        }
    });
    latitude1 = position.getLatitude1();
    longitude1 = position.getLongitude1();
    latitude2 = String.valueOf(latitude1);
    longitude2 = String.valueOf(longitude1);
    asyncTask.execute(latitude2, longitude2); //  asyncTask.execute("Latitude", "Longitude")

}

为什么我的安卓显示器上总是显示latitude2=0.0和Longtude2=0.0

Answer 1

无法共享私有变量。把它改成

public double longitude1;
public double latitude1;

Answer 2

我建议您在代码中添加以下改革

1. 您需要在MainActivity的onCreate（）方法内创建Position类的对象。由于onCreate（）在运行其他操作之前运行，因此有必要在该方法中定义Position类

2. 将经度和纬度的变量公开，以便在其他类中访问它们

3. Position类不需要扩展AppCompatActivity。您可以使用构造函数并在那里定义所有内容，而不是使用这个和OnCreate（）方法

Answer 3

您实际上不需要从活动中进行Position扩展。我可以理解您正在尝试做什么，您只需要从LocationManager获取位置，然后将结果发送到MainActivity。如果只在MainActivity中创建一个LocationManager实例，并将位置结果传递给MainActivity中所需的任何内容，就可以了

public class MainActivity extends AppCompatActivity {

TextView cityField, detailsField, currentTemperatureField, humidity_field, pressure_field, weatherIcon, updatedField;

Typeface weatherFont;

Position position = new Position();

private double latitude1;
private double longitude1;
private String latitude2;
private String longitude2;

private LocationManager mLocationManager;

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


    weatherFont = Typeface.createFromAsset(getApplicationContext().getAssets(), "fonts/weathericons-regular-webfont.ttf");

    cityField = (TextView)findViewById(R.id.city_field);
    updatedField = (TextView)findViewById(R.id.updated_field);
    detailsField = (TextView)findViewById(R.id.details_field);
    currentTemperatureField = (TextView)findViewById(R.id.current_temperature_field);
    humidity_field = (TextView)findViewById(R.id.humidity_field);
    pressure_field = (TextView)findViewById(R.id.pressure_field);
    weatherIcon = (TextView)findViewById(R.id.weather_icon);
    weatherIcon.setTypeface(weatherFont);


    mLocationManager = (LocationManager) getSystemService(LOCATION_SERVICE);

    // do check permission staff as you post before

    Location location = locationManager.getLastKnownLocation(locationManager.NETWORK_PROVIDER);

    // do what you want with the location now.

基本上，我认为您不必创建Position类。您可以直接获取位置，然后使用它

Answer 4

你有两种不同的活动。不是活动和后台服务。只有一个UI线程运行这些活动。因此，当MainActivity正在运行时，Position活动在后台并且没有运行。并且不能使用Position position = new Position();创建活动的对象

Answer 5

为什么你的Position类是Activity？除非将类作为Activity启动，否则将永远不会在那里调用onCreate方法。从中删除AppCompatActivity，并将onCreate方法移动到一个单独的方法中，例如getLocation

您还希望将Context传递给Position类。为此创建一个构造函数

public Position(Context context) {
    this.context = context;
}

并将其用于系统调用