Android 位置上的空对象引用

Question

好的，所以我正在使用来自 GPS.class 的这个 GPS 位置，并且我一直在获取空对象引用，但不确定 why.Here 是我的代码：

 boolean permissionGranted = ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED;

    if(permissionGranted)
    {
        if (GPS.sharedInstance(AppDashboard.this).canGetLocation() && GPS.sharedInstance(this).isPermissionEnabled()) {
            double lat = GPS.sharedInstance(AppDashboard.this).getLatitude();
            double lon = GPS.sharedInstance(AppDashboard.this).getLongitude();
            Log.e(TAG, "Location: " + lat + "/"+ lon);
        }
        else
        {
            Log.e(TAG, "Can't get GPS locations");
        }
    } else {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 200);
    }

我的清单：

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-feature android:name="android.hardware.location.gps" />

我的Logcat:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference
at com.gpsApp.utility.GPS.getLatitude(GPS.java:113)

和GPS Class 113

public double getLatitude() {
    if (_locationManager != null) {
        _latitude = _location.getLatitude();
    }

    return _latitude;
}

Answer 1

使用这一行

boolean permissionGranted = ActivityCompat.checkSelfPermission(getApplicationContext, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED;

而不是这个

 boolean permissionGranted = ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED;

Answer 2

您正在从 GPS class 调用 public double getLatitude()，但是 _location 变量未初始化，因此您得到 NullPointerException。

在呼叫 getLatitude() 之前，请尝试从您的 GPS class 呼叫 public Location getLastKnownLocation()。此调用将初始化 _location 变量。

Android 位置上的空对象引用

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