Chromium plumbing for Device Orientation.

chrome/browser/device_orientation/provider.h

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_
+#define CHROME_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_
+
+#include "base/logging.h"
+#include "base/ref_counted.h"
+
+namespace device_orientation {
+
+class Orientation;
+
+class Provider : public base::RefCounted<Provider> {
+ public:
+  class Observer {
+   public:
+    // Called when the orientation changes.
+    // An Observer must not synchronously call Provider::RemoveObserver
+    // or Provider::AddObserver when this is called.
+    virtual void OnOrientationUpdate(const Orientation& orientation) = 0;
+  };
+
+  // Returns a pointer to the singleton instance of this class.
+  // The caller should store the returned pointer in a scoped_refptr.
+  // The Provider instance is lazily constructed when GetInstance() is called,
+  // and destructed when the last scoped_refptr referring to it is destructed.
+  static Provider* GetInstance();
+
+  // Inject a mock Provider for testing. Only a weak pointer to the injected
+  // object will be held by Provider, i.e. it does not itself contribute to the
+  // injected object's reference count.
+  static void SetInstanceForTests(Provider* provider);
+
+  virtual void AddObserver(Observer* observer) {}
+  virtual void RemoveObserver(Observer* observer) {}
+
+ protected:
+  Provider() {}
+  virtual ~Provider() {
+    DCHECK(instance_ == this);
+    instance_ = NULL;
+  }
+
+ private:
+  friend class base::RefCounted<Provider>;
+  static Provider* instance_;
+
+  DISALLOW_COPY_AND_ASSIGN(Provider);
+};
+
+}  // namespace device_orientation
+
+#endif  // CHROME_BROWSER_DEVICE_ORIENTATION_PROVIDER_H_