Question

我正在尝试使用RectF和canvas.drawRoundRect（）绘制一个圆角矩形。请参阅下面的代码：

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);

        }
    }

}

程序运行但没有任何东西被绘制，即我只是得到我的白色背景屏幕。关于为什么的任何想法？

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，您的RectF代表Point而不是Rectangle，这就是您无法看到Rect ...

的原因

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

此处RectF是

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

此处left = right = 200和top = bottom = 400代表Point

如果您想绘制Rect width = 200和height = 400，那么您的RectF应为

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

对于width = 400 and height = 200，RectF应为

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

Answer 2

您尚未创建正确的矩形。给你的矩形正确的左，上，右，下点如：RectF rectf = new RectF(0, 0, 480, 854);

Answer 3

干杯队员。发现。我已经更正了我的代码，如下所示，现在我可以看到我的矩形了。

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(0, 0, 200, 300);
        CustomRectangle customRectangle = new CustomRectangle(this, rectf, 15, 15, "#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);

        }
    }

}

Answer 4

与Android Docs

一样

RectF为矩形保存四个浮点坐标。矩形由其4条边（左，上，右下）的坐标表示。

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

在代码段中，文档所说的RectF Arguments代表Rectangle的边坐标。

作为结论，
width = |左 - 右|
身高= |顶部 - 底部|

如果问题的宽度和高度为0，则它不代表视图或对象，
在逻辑上，对象不可能存在高度，宽度和深度为0.

使用RectF和canvas绘制圆角矩形？

4 个答案: