我有问题。在我的MainActivity中，单击按钮时会调用片段。片段之一是带有TriangleGrid的SkiaSharp画布。当您单击三角形时，它将更改该三角形的颜色。现在，当我第一次访问SkiaSharp片段时，一切都可以按我的要求正确加载，但是当我转到另一个页面然后返回SkiaSharp画布时，整个画布为空白。当您点击三角形时，三角形仍然充满，但是TriangleGrid消失了。也是之前单击的三角形，最后一个除外。这是我的代码中最重要的部分。
这是完整 MainActivity：
public class MainActivity : FragmentActivity
{
Dictionary<string, TriangleRegistryObject> TriangleRegistry = new Dictionary<string, TriangleRegistryObject>();
//ALL FRAGMENTS
private Android.Support.V4.App.Fragment CurrentFragment;
private int CurrentFragmentNum;
private int PreviousFragmentNum;
private Shape_Selection ShapeSelectionFragment;
private Shape_Formation ShapeFormationFragment;
private string Direction;
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
ActionBar.SetCustomView(Resource.Layout.setup_nav_bar);
ActionBar.SetDisplayShowCustomEnabled(true);
((Toolbar)ActionBar.CustomView.Parent).SetContentInsetsAbsolute(0, 0);
SetContentView(Resource.Layout.activity_main);
Button btnBack = FindViewById<Button>(Resource.Id.btnBack);
Button btnNext = FindViewById<Button>(Resource.Id.btnNext);
btnBack.Click += btnBack_Click;
btnNext.Click += btnNext_Click;
ShapeSelectionFragment = new Shape_Selection();
ShapeFormationFragment = new Shape_Formation();
var trans = SupportFragmentManager.BeginTransaction();
trans.Add(Resource.Id.fragmentContainer, ShapeFormationFragment, "Shape_Formation");
trans.Hide(ShapeFormationFragment);
trans.Add(Resource.Id.fragmentContainer, ShapeSelectionFragment, "Shape_Selection");
//trans.Hide(ShapeSelectionFragment);
trans.Commit();
CurrentFragmentNum = 1;
Direction = "Startup";
ShowFragment(CurrentFragmentNum, 1, Direction);
}
private void ShowFragment (int CurrentFragmentNum, int PreviousFragmentNum, string Direction)
{
Android.Support.V4.App.Fragment fragment = null;
Android.Support.V4.App.Fragment PreviousFragment = null;
switch (CurrentFragmentNum)
{
case 1:
fragment = ShapeSelectionFragment;
break;
case 2:
fragment = ShapeFormationFragment;
break;
}
switch (PreviousFragmentNum)
{
case 1:
PreviousFragment = ShapeSelectionFragment;
break;
case 2:
PreviousFragment = ShapeFormationFragment;
break;
}
var trans = SupportFragmentManager.BeginTransaction();
switch (Direction)
{
case "Forwards":
trans.SetCustomAnimations(Resource.Animation.slide_in_right, Resource.Animation.slide_out_left);
break;
case "Backwards":
trans.SetCustomAnimations(Resource.Animation.slide_in_left, Resource.Animation.slide_out_right);
break;
}
trans.Replace(Resource.Id.fragmentContainer, fragment);
trans.Hide(PreviousFragment);
trans.Show(fragment);
trans.AddToBackStack(null);
trans.Commit();
CurrentFragment = fragment;
if(CurrentFragment == ShapeSelectionFragment)
{
CurrentFragmentNum = 1;
}
else if (CurrentFragment == ShapeFormationFragment)
{
CurrentFragmentNum = 2;
}
}
public void btnBack_Click(object sender, EventArgs e)
{
if (CurrentFragmentNum > 1)
{
PreviousFragmentNum = CurrentFragmentNum;
CurrentFragmentNum -= 1;
Direction = "Backwards";
ShowFragment(CurrentFragmentNum, PreviousFragmentNum, Direction);
}
}
public void btnNext_Click(object sender, EventArgs e)
{
if (CurrentFragmentNum < 2)
{
PreviousFragmentNum = CurrentFragmentNum;
CurrentFragmentNum += 1;
Direction = "Forwards";
ShowFragment(CurrentFragmentNum, PreviousFragmentNum, Direction);
}
}
}
这是完整 Shape_Formation.cs：
public class Shape_Formation : Android.Support.V4.App.Fragment, IOnTouchListener
{
private SKCanvasView skiaView;
private SKPaint TriangleFillColor;
private string Action { get; set; }
Dictionary<string, TriangleRegistryObject> TriangleRegistry = new Dictionary<string, TriangleRegistryObject>();
private int UnscaledWidth;
private int UnscaledHeight;
private int TrianglesPerUpperRow;
private int TrianglesPerLowerRow;
private int TrianglesVisiblePerRow = 4;
private int CurrentRow = 0;
private float TriangleWidth;
private float TriangleRowHeight;
//ALL SHAPE PATHS
private SKPath TriangleGridPath = new SKPath();
private SKPath TrianglePath = new SKPath();
//================//
// PAINT VARIANTS //
//================//
SKPaint TriangleGridPaint = new SKPaint
{
Style = SKPaintStyle.Stroke,
Color = SKColors.White,
StrokeWidth = 3
};
SKPaint SelectTrianglePaint = new SKPaint
{
Style = SKPaintStyle.Fill,
Color = SKColors.Blue
};
SKPaint UnselectTrianglePaint = new SKPaint
{
Style = SKPaintStyle.Fill,
Color = SKColor.Parse("#0e2a56")
};
SKPaint BackgroundPaint = new SKPaint
{
Style = SKPaintStyle.Fill,
Color = SKColor.Parse("#0e2a56")
};
SKPaint FocusedTrianglePaint = new SKPaint
{
Style = SKPaintStyle.Fill,
Color = SKColors.LightGray
};
//=======================//
// END OF PAINT VARIANTS //
//=======================//
public override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
}
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.Inflate(Resource.Layout.setup_shape_formation, container, false);
skiaView = view.FindViewById<SKCanvasView>(Resource.Id.skiaView);
skiaView.SetOnTouchListener(this);
skiaView.PaintSurface += PaintSurface;
return view;
}
private void PaintSurface(object sender, SKPaintSurfaceEventArgs e)
{
//==============//
// CANVAS SETUP //
//==============//
SKCanvas canvas = e.Surface.Canvas;
//SOME VARIABLES OF SCREEN SIZE
UnscaledWidth = e.Info.Width;
UnscaledHeight = e.Info.Height;
//=====================//
// END OF CANVAS SETUP //
//=====================//
if (TriangleFillColor != null)
{
canvas.DrawPath(TrianglePath, TriangleFillColor);
canvas.DrawPath(TrianglePath, TriangleGridPaint);
}
//====================//
// DRAW TRIANGLE GRID //
//====================//
int TriangleCount = 0;
TriangleWidth = UnscaledWidth / TrianglesVisiblePerRow;
TriangleRowHeight = (float)Math.Sqrt(Math.Pow(TriangleWidth, 2) - (Math.Pow((UnscaledWidth / (TrianglesVisiblePerRow * 2)), 2)));
CurrentRow = 1;
float X_Start_CooridnateUpperRow = 0;
float Y_Start_CooridnateUpperRow = 0;
float X_Start_CooridnateLowerRow = -(TriangleWidth / 2);
float Y_Start_CooridnateLowerRow = TriangleRowHeight;
SKPaint TriangleBorderPaint;
//DRAW MULTIPLE ROWS
while (Y_Start_CooridnateUpperRow <= UnscaledHeight)
{
TrianglesPerUpperRow = 5;
TrianglesPerLowerRow = 5;
//SET THE TRIANGLE COUNTER FOR BOTH ROWS
int TriangleUpperCountOnRow = 0;
int TriangleLowerCountOnRow = 0;
//DRAW THE UPPER ROW OF TRIANGLES
while (TriangleUpperCountOnRow < TrianglesPerUpperRow)
{
float x1 = X_Start_CooridnateUpperRow;
float y1 = Y_Start_CooridnateUpperRow;
float x2 = X_Start_CooridnateUpperRow + TriangleWidth;
float y2 = y1;
float x3 = X_Start_CooridnateUpperRow + TriangleWidth / 2;
float y3 = TriangleRowHeight * (CurrentRow);
TriangleGridPath = new SKPath();
TriangleGridPath.MoveTo(x1, y1);
TriangleGridPath.LineTo(x2, y2);
TriangleGridPath.LineTo(x3, y3);
TriangleGridPath.LineTo(x1, y1);
TriangleGridPath.Close();
TriangleRegistryObject value;
TriangleRegistry.TryGetValue(TriangleCount.ToString(), out value);
if (value == null)
{
if (x1 > UnscaledWidth ||
x2 > UnscaledWidth ||
x3 > UnscaledWidth ||
x1 < 0 ||
x2 < 0 ||
x3 < 0 ||
y1 > UnscaledHeight ||
y2 > UnscaledHeight ||
y3 > UnscaledHeight)
{
TriangleBorderPaint = BackgroundPaint;
TriangleRegistry[TriangleCount.ToString()] = new TriangleRegistryObject { x1 = x1, y1 = y1, x2 = x2, y2 = y2, x3 = x3, y3 = y3, Selected = false, Visible = false };
}
else
{
TriangleBorderPaint = TriangleGridPaint;
TriangleRegistry[TriangleCount.ToString()] = new TriangleRegistryObject { x1 = x1, y1 = y1, x2 = x2, y2 = y2, x3 = x3, y3 = y3, Selected = false, Visible = true };
}
canvas.DrawPath(TriangleGridPath, TriangleBorderPaint);
}
TriangleCount += 1;
TriangleUpperCountOnRow += 1;
X_Start_CooridnateUpperRow += TriangleWidth;
}
//DRAW THE LOWER ROW OF TRIANGLES
while (TriangleLowerCountOnRow < TrianglesPerLowerRow)
{
float x1 = X_Start_CooridnateLowerRow;
float y1 = Y_Start_CooridnateLowerRow;
float x2 = X_Start_CooridnateLowerRow + TriangleWidth;
float y2 = y1;
float x3 = X_Start_CooridnateLowerRow + (TriangleWidth / 2);
float y3 = TriangleRowHeight * (CurrentRow - 1);
TriangleGridPath = new SKPath();
TriangleGridPath.MoveTo(x1, y1);
TriangleGridPath.LineTo(x2, y2);
TriangleGridPath.LineTo(x3, y3);
TriangleGridPath.LineTo(x1, y1);
TriangleGridPath.Close();
TriangleRegistryObject value;
TriangleRegistry.TryGetValue(TriangleCount.ToString(), out value);
if (value == null)
{
if (x1 > UnscaledWidth ||
x2 > UnscaledWidth ||
x3 > UnscaledWidth ||
x1 < 0 ||
x2 < 0 ||
x3 < 0 ||
y1 > UnscaledHeight ||
y2 > UnscaledHeight ||
y3 > UnscaledHeight)
{
TriangleBorderPaint = BackgroundPaint;
TriangleRegistry[TriangleCount.ToString()] = new TriangleRegistryObject { x1 = x1, y1 = y1, x2 = x2, y2 = y2, x3 = x3, y3 = y3, Selected = false, Focused = false, Visible = false };
}
else
{
TriangleBorderPaint = TriangleGridPaint;
TriangleRegistry[TriangleCount.ToString()] = new TriangleRegistryObject { x1 = x1, y1 = y1, x2 = x2, y2 = y2, x3 = x3, y3 = y3, Selected = false, Focused = false, Visible = true };
}
canvas.DrawPath(TriangleGridPath, TriangleBorderPaint);
}
TriangleCount += 1;
TriangleLowerCountOnRow += 1;
X_Start_CooridnateLowerRow += TriangleWidth;
}
CurrentRow += 1;
if ((CurrentRow - 1) % 2 != 0)
{
X_Start_CooridnateUpperRow = -(TriangleWidth / 2);
X_Start_CooridnateLowerRow = 0;
}
else
{
X_Start_CooridnateUpperRow = 0;
X_Start_CooridnateLowerRow = -(TriangleWidth / 2);
}
Y_Start_CooridnateUpperRow += TriangleRowHeight;
Y_Start_CooridnateLowerRow += TriangleRowHeight;
}
//==============================//
// END OF DRAWING TRIANGLE GRID //
//==============================//
}
public override void OnDestroy()
{
skiaView.PaintSurface -= PaintSurface;
base.OnDestroy();
}
private void DrawTrianglePath(double x1, double y1, double x2, double y2, double x3, double y3, string key, string Action)
{
bool ChangedState = true;
var Triangle = TriangleRegistry[key];
if (Triangle.Visible == true)
{
if (Triangle.Selected == false)
{
if (Action == "Selected")
{
Triangle.Selected = true;
TriangleRegistry[key] = Triangle;
TriangleFillColor = SelectTrianglePaint;
}
else if (Action == "Focused")
{
if (Triangle.Focused == false)
{
Triangle.Focused = true;
TriangleRegistry[key] = Triangle;
TriangleFillColor = FocusedTrianglePaint;
}
}
}
else
{
Triangle.Selected = false;
TriangleFillColor = UnselectTrianglePaint;
}
if (ChangedState == true)
{
TrianglePath = new SKPath();
TrianglePath.MoveTo((float)Triangle.x1, (float)Triangle.y1);
TrianglePath.LineTo((float)Triangle.x2, (float)Triangle.y2);
TrianglePath.LineTo((float)Triangle.x3, (float)Triangle.y3);
TrianglePath.LineTo((float)Triangle.x1, (float)Triangle.y1);
TrianglePath.Close();
skiaView.Invalidate();
}
}
}
public bool OnTouch(View v, MotionEvent e)
{
if (e.Action == MotionEventActions.Down)
{
var X_Clicked = e.GetX();
var Y_Clicked = e.GetY();
bool TriangleFound = false;
while (TriangleFound == false)
{
foreach (KeyValuePair<string, TriangleRegistryObject> row in TriangleRegistry.ToList())
{
if (isInside(row.Value.x1, row.Value.y1, row.Value.x2, row.Value.y2, row.Value.x3, row.Value.y3, X_Clicked, Y_Clicked))
{
TriangleFound = true;
Action = "Selected";
DrawTrianglePath(row.Value.x1, row.Value.y1, row.Value.x2, row.Value.y2, row.Value.x3, row.Value.y3, row.Key, Action);
}
}
}
}
return true;
}
static double area(double x1, double y1, double x2, double y2, double x3, double y3)
{
return Math.Abs((x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2.0);
}
static bool isInside(double x1, double y1, double x2, double y2, double x3, double y3, double x, double y)
{
double A = area(x1, y1, x2, y2, x3, y3);
double A1 = area(x, y, x2, y2, x3, y3);
double A2 = area(x1, y1, x, y, x3, y3);
/* Calculate area of triangle PAB */
double A3 = area(x1, y1, x2, y2, x, y);
/* Check if sum of A1, A2 and A3 is same as A */
return (A == A1 + A2 + A3);
}
}
有人可以帮助我解决这个问题吗？？
答案 0 :(得分：1)
您可以在ShowFragment中看到以下代码行：
trans.Replace(Resource.Id.fragmentContainer, fragment);
trans.Hide(PreviousFragment);
trans.Show(fragment);
trans.AddToBackStack(null);
trans.Commit();
您使用replace，它将破坏您之前在Resource.Id.fragmentContainer中添加的片段，因此它无法存储画布，这里您只想显示和隐藏之前添加的片段，您可以像这样进行更改（这不会破坏片段而是隐藏并显示）：
trans.Hide(PreviousFragment);
trans.Show(fragment);
trans.Commit();