android - 使用 RectF 和 Canvas 绘制圆角矩形？

Question

我正在尝试使用 RectF 和 canvas.drawRoundRect() 绘制一个圆角矩形。请在下面查看我的代码:

package com.example.test;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.RelativeLayout;
import android.graphics.RectF;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Create main RL params
        RelativeLayout.LayoutParams rlMainlayoutParams 
                = new RelativeLayout.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);

        // Create main relative layout
        RelativeLayout rlMain = new RelativeLayout(this);
        rlMain.setLayoutParams(rlMainlayoutParams);
        //rlMain.setBackgroundResource(R.drawable.bgndlogin);
        rlMain.setBackgroundColor(Color.WHITE);

        RectF rectf = new RectF(200, 400, 200, 400);
        CustomRectangle customRectangle = new CustomRectangle(this, rectf, 5, 5, "#FFFF00");

        //
        rlMain.addView(customRectangle);

        setContentView(rlMain);
    }

    //!< Draw the log in rectangle shaped panel
    public class CustomRectangle extends View {
        Paint paint;
        float left_side, top_side;
        String color;
        RectF rectf;

        //!< Constructor for the log in rectangle shaped panel
        public CustomRectangle(Context context, RectF rectf, float left_side, float top_side, String color) {
            super(context);

            this.rectf = rectf;
            this.left_side= left_side;
            this.top_side = top_side;
            this.color = color;

        }

        //!< Implement to draw the rectangle
        @Override
        public void onDraw(Canvas canvas) {
            paint = new Paint();
            paint.setColor(Color.parseColor(color));
            paint.setStrokeWidth(3);
            //paint.setAlpha(61);

            canvas.drawRoundRect(rectf, left_side, top_side, paint);

        }
    }

}

程序运行但没有绘制任何东西，即我只是得到我的白色背景屏幕。关于原因有什么想法吗？

注意:我以编程方式创建相对布局，而不是使用 XML 进行缩放。

Answer 1

实际上这里你的 RectF 代表 Point 而不是 Rectangle，这就是为什么你看不到 Rect.. .

RectF rectF = new RectF(left, top, right, bottom);

这里 RectF 是

RectF rectf = new RectF(200, 400, 200, 400); // representing Point

这里 left = right = 200 和 top = bottom = 400 代表一个 Point

如果你想画一个width = 200和height = 400的Rect，那么你的RectF应该是

RectF rectf = new RectF(0, 0, 200, 400);

对于 width = 400 and height = 200，RectF 应该是

RectF rectf = new RectF(0, 0, 400, 200);