c# - 如何在 Xamarin iOS 中绘制文本？
<p><p>我想在自定义 <code>View</code> 的 <code>Draw</code> 方法中的给定点 (x, y) 处绘制文本。</p>
<p>我关注了<a href="https://developer.xamarin.com/recipes/ios/graphics_and_drawing/core_text/draw_unicode_text_with_coretext/" rel="noreferrer noopener nofollow">this sample</a>来自 Xamarin 网站。 </p>
<p>这是我创建的 View :</p>
<pre><code>public class MyView : UIView
{
public override void Draw(CGRect rect)
{
using (var context = UIGraphics.GetCurrentContext())
{
DrawText(context, "hello", 20, new CGPoint(0, 0));
DrawText(context, "how are you", 20, new CGPoint(0, 40));
}
}
private void DrawText(CGContext context, string text, int textHeight, CGPoint point)
{
var x = point.X;
var y = point.Y + textHeight;
context.TranslateCTM(x, y);
context.ScaleCTM(1, -1);
context.SetFillColor(UIColor.Red.CGColor);
var attributedString = new NSAttributedString(text,
new CTStringAttributes
{
ForegroundColorFromContext = true,
Font = new CTFont("Arial", 16)
});
using (var textLine = new CTLine(attributedString))
{
textLine.Draw(context);
}
}
}
</code></pre>
<p>问题在于 <code>DrawText</code> 方法<strong>只能正常工作一次</strong>。第一次调用它时，会绘制文本，但<strong>它在连续调用时不起作用</strong>(它什么也不绘制，或者它绘制的内容不可见)。</p>
<p>我做错了什么？</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>因此，您的代码有两个基本问题。</p>
<ul>
<li>每次调用 <code>DrawText</code></li> 时，您都在执行 <code>ScaleCTM</code> 和 <code>TranslateCTM</code>
<li>您没有考虑到，当您<code>CTLine.Draw</code> 时，“光标”会移动到该文本的末尾。</li>
</ul>
<p>所以，调用 <code>ScaleCTM</code> 来翻转整个东西，使文本从左到右绘制，然后调用 <code>DrawText</code> 并转换到您要绘制文本的位置，然后 <strong >翻译回</strong>到您开始的位置，以便下次您在同一点。</p>
<h3>示例绘制覆盖:</h3>
<pre><code>public override void Draw(CGRect rect)
{
var context = UIGraphics.GetCurrentContext();
context.ScaleCTM(1, -1); // you flipped the context, now you must use negative Y values to draw "into" the view
var textHeight = new CTFont("Arial", 16).CapHeightMetric; // lets use the actaul height of the font captials.
DrawText(context, "Hello", textHeight, 0, 0);
DrawText(context, "How are you?", textHeight, 0, 20);
DrawText(context, "Sincerely,", textHeight, 0, 40);
DrawText(context, "StackOverflow,", textHeight, 0, 60);
}
void DrawText(CGContext context, string text, nfloat textHeight, nfloat x, nfloat y)
{
context.TranslateCTM(-x, -(y + textHeight));
context.SetFillColor(UIColor.Red.CGColor);
var attributedString = new NSAttributedString(text,
new CTStringAttributes
{
ForegroundColorFromContext = true,
Font = new CTFont("Arial", 16)
});
CGRect sizeOfText;
using (var textLine = new CTLine(attributedString))
{
textLine.Draw(context);
sizeOfText = textLine.GetBounds(CTLineBoundsOptions.UseOpticalBounds);
}
// Reset the origin back to where is was
context.TranslateCTM(x - sizeOfText.Width, y + sizeOfText.Height);
}
</code></pre>
<h3>结果:</h3>
<p> <a href="/image/mgJii.png" rel="noreferrer noopener nofollow"><img src="/image/mgJii.png" alt="enter image description here"/></a> </p>
<h3>使用 NSMutableParagraphStyle 和 NSString.DrawString</h3>
<pre><code>var context = UIGraphics.GetCurrentContext();
CGRect textRect = new CGRect(0.0f, 0.0f, 200.0f, 100.0f);
{
var textContent = "Hello\nHow are you?\nSincerely,\nStackOverflow";
UIColor.Red.SetFill();
var textStyle = new NSMutableParagraphStyle ();
textStyle.Alignment = UITextAlignment.Left;
var textFontAttributes = new UIStringAttributes () {Font = UIFont.FromName("ArialMT", 16.0f), ForegroundColor = UIColor.Red, ParagraphStyle = textStyle};
var textTextHeight = new NSString(textContent).GetBoundingRect(new CGSize(textRect.Width, nfloat.MaxValue), NSStringDrawingOptions.UsesLineFragmentOrigin, textFontAttributes, null).Height;
context.SaveState();
context.ClipToRect(textRect);
new NSString(textContent).DrawString(new CGRect(textRect.GetMinX(), textRect.GetMinY() + (textRect.Height - textTextHeight) / 2.0f, textRect.Width, textTextHeight), UIFont.FromName("ArialMT", 16.0f), UILineBreakMode.WordWrap, UITextAlignment.Left);
context.RestoreState();
}
</code></pre></p>
<p style="font-size: 20px;">关于c# - 如何在 Xamarin iOS 中绘制文本？，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/44400322/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/44400322/
</a>
</p>
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