Android 网络定位流程

        上一篇我们记录了 GPS 的定位流程，这一篇记录下 NLP（Network Location Provider）的定位流程，因为在国内，无法使用谷歌提供的NLP，所以国内我们一般会使用三方提供的NLP，比如：百度、高德、腾讯等。

        这里我们假设一个app发起 NLP 定位，首先调用 LocationManager 接口，通过AIDL最终调用到 LocationManagerService 里面的  requestLocationUpdates 方法：

http://androidxref.com/9.0.0_r3/xref/frameworks/base/location/java/android/location/LocationManager.java#requestLocationUpdates

    public void requestLocationUpdates(String provider, long minTime, float minDistance,
            LocationListener listener) {
        checkProvider(provider);
        checkListener(listener);

        LocationRequest request = LocationRequest.createFromDeprecatedProvider(
                provider, minTime, minDistance, false);
        requestLocationUpdates(request, listener, null, null);
    }

到这里我们就知道了，不管是GPS还是NLP，调用的都是这个接口，区别就是传进去的参数不一样，例如：provider，在Android 里面我们有以下几种provider：

Gps_provider、Network_provider、Passive_provider、Fused_provider、Mock_provider，其中前三种比较常用，Fused_provider依赖三方，比如谷歌GMS包。Mock_provider就是我们常说的伪造位置，一些虚拟定位软件就是基于这个开发的，这里我们暂时不记录，需要的后续单独详细讲。

继续看流程调用：

http://androidxref.com/9.0.0_r3/xref/frameworks/base/services/core/java/com/android/server/LocationManagerService.java#requestLocationUpdates

    public void requestLocationUpdates(LocationRequest request, ILocationListener listener,
            PendingIntent intent, String packageName) {
        if (request == null) request = DEFAULT_LOCATION_REQUEST;
        checkPackageName(packageName);
        int allowedResolutionLevel = getCallerAllowedResolutionLevel();
        checkResolutionLevelIsSufficientForProviderUse(allowedResolutionLevel,
                request.getProvider());
        WorkSource workSource = request.getWorkSource();
        if (workSource != null && !workSource.isEmpty()) {
            checkDeviceStatsAllowed();
        }
        boolean hideFromAppOps = request.getHideFromAppOps();
        if (hideFromAppOps) {
            checkUpdateAppOpsAllowed();
        }
        boolean callerHasLocationHardwarePermission =
                mContext.checkCallingPermission(android.Manifest.permission.LOCATION_HARDWARE)
                        == PERMISSION_GRANTED;
        LocationRequest sanitizedRequest = createSanitizedRequest(request, allowedResolutionLevel,
                callerHasLocationHardwarePermission);

        final int pid = Binder.getCallingPid();
        final int uid = Binder.getCallingUid();
        // providers may use public location API's, need to clear identity
        long identity = Binder.clearCallingIdentity();
        try {
            // We don't check for MODE_IGNORED here; we will do that when we go to deliver
            // a location.
            checkLocationAccess(pid, uid, packageName, allowedResolutionLevel);

            synchronized (mLock) {
                Receiver recevier = checkListenerOrIntentLocked(listener, intent, pid, uid,
                        packageName, workSource, hideFromAppOps);
                requestLocationUpdatesLocked(sanitizedRequest, recevier, pid, uid, packageName);
            }
        } finally {
            Binder.restoreCallingIdentity(identity);
        }
    }

这个流程其实都是一样的和GPS，最终到 applyRequirementsLocked 方法里这个地方，之前讲过：P指的是 LocationProviderInterface接口，而所有的provider要实现它，而这里我们请求的是网络 provider，此时网络的provider是三方实现的，就会走到具体实现的地方

        if (D) Log.d(TAG, "provider request: " + provider + " " + providerRequest);
        p.setRequest(providerRequest, worksource);

 而 LocationManagerService 在 systemRunning 的时候就去bind 三方的包，这样在请求Network_provider的时候就是走到绑定的三方接口里

        // bind to network provider
        LocationProviderProxy networkProvider = LocationProviderProxy.createAndBind(
                mContext,
                LocationManager.NETWORK_PROVIDER,
                NETWORK_LOCATION_SERVICE_ACTION,
                com.android.internal.R.bool.config_enableNetworkLocationOverlay,
                com.android.internal.R.string.config_networkLocationProviderPackageName,
                com.android.internal.R.array.config_locationProviderPackageNames,
                mLocationHandler);
        if (networkProvider != null) {
            mRealProviders.put(LocationManager.NETWORK_PROVIDER, networkProvider);
            mProxyProviders.add(networkProvider);
            addProviderLocked(networkProvider);
        } else {
            Slog.w(TAG, "no network location provider found");
        }

 至此，大致流程梳理完毕。

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