Android 获取判断是否有悬浮窗权限的方法

现在很多应用都会用到悬浮窗，很多国产rom把悬浮窗权限加入控制了，你就需要判断是否有悬浮窗权限，然后做对应操作。

Android 原生有自带权限管理的，只是被隐藏了。看android源码在android.app下就有个AppOpsManager类。

类说明如下：

/**
 * API for interacting with "application operation" tracking.
 *
 * <p>This API is not generally intended for third party application developers; most
 * features are only available to system applications. Obtain an instance of it through
 * {@link Context#getSystemService(String) Context.getSystemService} with
 * {@link Context#APP_OPS_SERVICE Context.APP_OPS_SERVICE}.</p>
 */

上面说明了只对系统应用有用，rom厂商们应该就是利用这个AppOps机制开放一些权限控制。

我们要判断是否有权限该如何做呢？就只能通过反射去判断了。

AppOpsManager的checkOp方法，就是检测是否有某项权限的方法有这些返回值，分别是允许，忽略，错误和默认：

/**
 * Result from {@link #checkOp}, {@link #noteOp}, {@link #startOp}: the given caller is
 * allowed to perform the given operation.
 */
public static final int MODE_ALLOWED = 0;

/**
 * Result from {@link #checkOp}, {@link #noteOp}, {@link #startOp}: the given caller is
 * not allowed to perform the given operation, and this attempt should
 * <em>silently fail</em> (it should not cause the app to crash).
 */
public static final int MODE_IGNORED = 1;

/**
 * Result from {@link #checkOpNoThrow}, {@link #noteOpNoThrow}, {@link #startOpNoThrow}: the
 * given caller is not allowed to perform the given operation, and this attempt should
 * cause it to have a fatal error, typically a {@link SecurityException}.
 */
public static final int MODE_ERRORED = 2;

/**
 * Result from {@link #checkOp}, {@link #noteOp}, {@link #startOp}: the given caller should
 * use its default security check. This mode is not normally used; it should only be used
 * with appop permissions, and callers must explicitly check for it and deal with it.
 */
public static final int MODE_DEFAULT = 3;

只有MODE_ALLOWED才是确定有权限的。

类里面checkOp方法如下，三个参数分别是操作id，uid和包名：

/**
 * Do a quick check for whether an application might be able to perform an operation.
 * This is <em>not</em> a security check; you must use {@link #noteOp(int, int, String)}
 * or {@link #startOp(int, int, String)} for your actual security checks, which also
 * ensure that the given uid and package name are consistent. This function can just be
 * used for a quick check to see if an operation has been disabled for the application,
 * as an early reject of some work. This does not modify the time stamp or other data
 * about the operation.
 * @param op The operation to check. One of the OP_* constants.
 * @param uid The user id of the application attempting to perform the operation.
 * @param packageName The name of the application attempting to perform the operation.
 * @return Returns {@link #MODE_ALLOWED} if the operation is allowed, or
 * {@link #MODE_IGNORED} if it is not allowed and should be silently ignored (without
 * causing the app to crash).
 * @throws SecurityException If the app has been configured to crash on this op.
 * @hide
 */
public int checkOp(int op, int uid, String packageName) {
 try {
  int mode = mService.checkOperation(op, uid, packageName);
  if (mode == MODE_ERRORED) {
   throw new SecurityException(buildSecurityExceptionMsg(op, uid, packageName));
  }
  return mode;
 } catch (RemoteException e) {
 }
 return MODE_IGNORED;
}

操作id即op可以在该类中找到静态值定义，android23里面有62种权限，我们需要的是OP_SYSTEM_ALERT_WINDOW=24

知道这些就可以用反射把我们的方法写出了：

 /**
  * 判断 悬浮窗口权限是否打开
  *
  * @param context
  * @return true 允许 false禁止
  */
 public static boolean getAppOps(Context context) {
  try {
   Object object = context.getSystemService("appops");
   if (object == null) {
    return false;
   }
   Class localClass = object.getClass();
   Class[] arrayOfClass = new Class[3];
   arrayOfClass[0] = Integer.TYPE;
   arrayOfClass[1] = Integer.TYPE;
   arrayOfClass[2] = String.class;
   Method method = localClass.getMethod("checkOp", arrayOfClass);
   if (method == null) {
    return false;
   }
   Object[] arrayOfObject1 = new Object[3];
   arrayOfObject1[0] = Integer.valueOf(24);
   arrayOfObject1[1] = Integer.valueOf(Binder.getCallingUid());
   arrayOfObject1[2] = context.getPackageName();
   int m = ((Integer) method.invoke(object, arrayOfObject1)).intValue();
   return m == AppOpsManager.MODE_ALLOWED;
  } catch (Exception ex) {

  }
  return false;
 }

测试在魅族华为小米大部分机型上都是可以的，但这个方法也不能保证正确，一些机型上会返回错误即MODE_ERRORED，就是获取不到权限值，这个方法就返回了false，但实际上悬浮窗是可以使用的。

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