如何在Android中通过canvas绘制圆圈？

我想通过canvas画圈。 这是我的代码：

[MyActivity.java]：

public class MyActivity extends Activity { public void onCreate(Bundle savedInstanceState) { ... setContentView(new View(this,w,h)); } } 

[View.java]：

 public class View extends SurfaceView { public View(Context context, int w, int h) { super(context); Canvas grid = new Canvas(Bitmap.createBitmap(h,w, Bitmap.Config.ARGB_8888)); grid. drawColor(Color.WHITE); Paint paint = new Paint(); paint.setStyle(Paint.Style.FILL); grid.drawCircle(w/2, h/2 , w/2, paint); } } 

所以我只是黑屏没有圈子。 为什么它不起作用？ 如何解决它？

Answer 1

您可以重写视图的onDraw方法并绘制圆。

 protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawCircle(x, y, radius, paint); } 

有关绘制自定义视图的更好参考，请查看官方的Android文档。

http://developer.android.com/training/custom-views/custom-drawing.html

Answer 2

 import android.app.Activity; import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.os.Bundle; import android.view.View; public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(new MyView(this)); } public class MyView extends View { Paint paint = null; public MyView(Context context) { super(context); paint = new Paint(); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); int x = getWidth(); int y = getHeight(); int radius; radius = 100; paint.setStyle(Paint.Style.FILL); paint.setColor(Color.WHITE); canvas.drawPaint(paint); // Use Color.parseColor to define HTML colors paint.setColor(Color.parseColor("#CD5C5C")); canvas.drawCircle(x / 2, y / 2, radius, paint); } } } 

如果要在中心绘制圆形，请编辑 。 您也可以将您的整个canvas翻译为中心，然后在中心画圆

 canvas.translate(getWidth()/2f,getHeight()/2f); canvas.drawCircle(0,0, radius, paint); 

这两个链接也有帮助

http://www.compiletimeerror.com/2013/09/introduction-to-2d-drawing-in-android.html#.VIg_A5SSy9o

http://android-coding.blogspot.com/2012/04/draw-circle-on-canvas-canvasdrawcirclet.html

Answer 3

 public class CircleView extends View { private static final String COLOR_HEX = "#E74300"; private final Paint drawPaint; private float size; public CircleView(final Context context, final AttributeSet attrs) { super(context, attrs); drawPaint = new Paint(); drawPaint.setColor(Color.parseColor(COLOR_HEX)); drawPaint.setAntiAlias(true); setOnMeasureCallback(); } @Override protected void onDraw(final Canvas canvas) { super.onDraw(canvas); canvas.drawCircle(size, size, size, drawPaint); } private void setOnMeasureCallback() { ViewTreeObserver vto = getViewTreeObserver(); vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() { @Override public void onGlobalLayout() { removeOnGlobalLayoutListener(this); size = getMeasuredWidth() / 2; } }); } @TargetApi(Build.VERSION_CODES.JELLY_BEAN) private void removeOnGlobalLayoutListener(ViewTreeObserver.OnGlobalLayoutListener listener) { if (Build.VERSION.SDK_INT < 16) { getViewTreeObserver().removeGlobalOnLayoutListener(listener); } else { getViewTreeObserver().removeOnGlobalLayoutListener(listener); } } } 

xml例子：会产生一圈5dp

  <com.example.CircleView android:layout_width="10dp" android:layout_height="10dp"/> 

Answer 4

 @Override public void onDraw(Canvas canvas){ canvas.drawCircle(xPos, yPos,radius, paint); } 

以上是渲染一个圆的代码。 调整参数到你的西装。

Answer 5

尝试这个

整个代码绘制一个圈或下载项目的源代码，并在您的Android工作室进行testing。 以编程方式在canvas上绘制圆。

 import android.graphics.Bitmap; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Path; import android.graphics.Point; import android.graphics.PorterDuff; import android.graphics.PorterDuffXfermode; import android.graphics.Rect; import android.graphics.RectF; import android.widget.ImageView; public class Shape { private Bitmap bmp; private ImageView img; public Shape(Bitmap bmp, ImageView img) { this.bmp=bmp; this.img=img; onDraw(); } private void onDraw(){ Canvas canvas=new Canvas(); if (bmp.getWidth() == 0 || bmp.getHeight() == 0) { return; } int w = bmp.getWidth(), h = bmp.getHeight(); Bitmap roundBitmap = getRoundedCroppedBitmap(bmp, w); img.setImageBitmap(roundBitmap); } public static Bitmap getRoundedCroppedBitmap(Bitmap bitmap, int radius) { Bitmap finalBitmap; if (bitmap.getWidth() != radius || bitmap.getHeight() != radius) finalBitmap = Bitmap.createScaledBitmap(bitmap, radius, radius, false); else finalBitmap = bitmap; Bitmap output = Bitmap.createBitmap(finalBitmap.getWidth(), finalBitmap.getHeight(), Bitmap.Config.ARGB_8888); Canvas canvas = new Canvas(output); final Paint paint = new Paint(); final Rect rect = new Rect(0, 0, finalBitmap.getWidth(), finalBitmap.getHeight()); paint.setAntiAlias(true); paint.setFilterBitmap(true); paint.setDither(true); canvas.drawARGB(0, 0, 0, 0); paint.setColor(Color.parseColor("#BAB399")); canvas.drawCircle(finalBitmap.getWidth() / 2 + 0.7f, finalBitmap.getHeight() / 2 + 0.7f, finalBitmap.getWidth() / 2 + 0.1f, paint); paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN)); canvas.drawBitmap(finalBitmap, rect, rect, paint); return output; }