我希望在我的应用程序相机页面中，当用户手动对焦（轻触对焦）时显示一个基本的圆形。
我已经实现了下面的自动对焦，但我不知道如何在焦点上绘制圆圈，并在视图变得无焦点时将其取消，同时在相机对焦时保持重新绘制。指示器不应是最终照片的一部分，只是在相机聚焦或未聚焦时向用户提供指导。
这是我目前的代码：
public class AutoFocusCallback : Java.Lang.Object, IAutoFocusCallback
{
public void OnAutoFocus(bool success, Android.Hardware.Camera camera)
{
var parameters = camera.GetParameters();
var supportedFocusModes = parameters.SupportedFocusModes;
if (string.IsNullOrEmpty(parameters.FocusMode))
{
string focusModeContinuous = Android.Hardware.Camera.Parameters.FocusModeContinuousPicture;
string focusModeAuto = Android.Hardware.Camera.Parameters.FocusModeAuto;
if (supportedFocusModes != null && supportedFocusModes.Any())
{
if (supportedFocusModes.Contains(focusModeContinuous))
{
parameters.FocusMode = focusModeContinuous;
}
else if (supportedFocusModes.Contains(focusModeAuto))
{
parameters.FocusMode = focusModeAuto;
}
}
}
if (supportedFocusModes != null && supportedFocusModes.Any())
{
if (parameters.MaxNumFocusAreas > 0)
{
parameters.FocusAreas = null;
}
if (success)
{
CameraPage cameraPage = new CameraPage();
Canvas canvas = new Canvas();
cameraPage.Draw(canvas);
}
camera.SetParameters(parameters);
camera.StartPreview();
}
}
}
public bool OnTouch(Android.Views.View v, MotionEvent e)
{
if (camera != null)
{
var parameters = camera.GetParameters();
camera.CancelAutoFocus();
Rect focusRect = CalculateTapArea(e.GetX(), e.GetY(), 1f);
if (parameters.FocusMode != Android.Hardware.Camera.Parameters.FocusModeAuto)
{
parameters.FocusMode = Android.Hardware.Camera.Parameters.FocusModeAuto;
}
if (parameters.MaxNumFocusAreas > 0)
{
List<Area> mylist = new List<Area>();
mylist.Add(new Android.Hardware.Camera.Area(focusRect, 1000));
parameters.FocusAreas = mylist;
}
try
{
camera.CancelAutoFocus();
camera.SetParameters(parameters);
camera.StartPreview();
camera.AutoFocus(new AutoFocusCallback());
}
catch (System.Exception ex)
{
Console.WriteLine(ex.ToString());
Console.Write(ex.StackTrace);
}
return true;
}
else
{
return false;
}
}
private Rect CalculateTapArea(object x, object y, float coefficient)
{
var focusAreaSize = Math.Max(textureView.Width, textureView.Height) / 8; //Recommended focus area size from the manufacture is 1/8 of the image
int areaSize = focusAreaSize * (int)coefficient;
int left = clamp(Convert.ToInt32(x) - areaSize / 2, 0, textureView.Width - areaSize);
int top = clamp(Convert.ToInt32(y) - areaSize / 2, 0, textureView.Height - areaSize);
RectF rectF = new RectF(left, top, left + areaSize, top + areaSize);
Matrix.MapRect(rectF);
return new Rect((int)System.Math.Round(rectF.Left), (int)System.Math.Round(rectF.Top), (int)System.Math.Round(rectF.Right), (int)System.Math.Round(rectF.Bottom));
}
private int clamp(int x, int min, int max)
{
if (x > max)
{
return max;
}
if (x < min)
{
return min;
}
return x;
}
public override void Draw(Canvas canvas)
{
base.Draw(canvas);
Paint p = new Paint();
p.Color = Android.Graphics.Color.White;
p.SetStyle(Paint.Style.Stroke);
p.StrokeWidth = 3;
canvas.DrawCircle(300, 300, 100, p);
}
例如，就像这张图片中所示：
这是为我的Xamarin.Forms Android应用程序设计的。
编辑：这里提供了相机的Android源代码，但不确定他们在哪里制作指示器：
类似的SO帖子没有官方答案：
正如您所看到的，有很多人有同样的问题，但没有答案！ 如果我还没讲清楚，请告诉我吧。
