我如何在Android的画布上绘制折线？

Question

我一直在尝试在画布上绘制折线。我的代码中没有错误，但是未显示所连接的线段顺序。请在下面找到代码段；

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.view.View;

public class MyView extends View {
    private Paint redPaint;

    public MyView(Context context) {
        super(context, null);
        redPaint=new Paint(Paint.ANTI_ALIAS_FLAG);
        redPaint.setStyle(Paint.Style.STROKE);
        redPaint.setColor(0xffff0000);
        redPaint.setStrokeWidth(5);

    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawRect(10,30,200,200,redPaint);
        canvas.drawCircle(300,300,250,redPaint);

        Path mylines=new Path();
        mylines.moveTo(0,0);
        mylines.lineTo(1,1);
        mylines.lineTo(2,2);
        mylines.lineTo(3,3);
        mylines.lineTo(4,4);
        Paint GreenPaint=new Paint();
        GreenPaint.setARGB(255,0,255,0);
        canvas.drawPath(mylines,GreenPaint);

    }
}

Answer 1

您的代码在很大程度上是正确的。您没有像GreenPaint那样完全初始化redPaint，这是一个问题。第二个问题虽然可能不是问题，但它的折线形状太小，即使使用完全初始化的GreenPaint，您也可能会错过它。

这里是自定义视图的更新版本，带有附加的构造函数和初始化的greenPaint。我还更改了折线的形状，使其变大以便于查看-这只是代码中的斑点。另外，我将对象分配移出了onDraw()。

    public class MyView extends View {
    Path mylines = new Path();
    private Paint redPaint;
    private Paint greenPaint;

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public MyView(Context context) {
        super(context, null);
        init();
    }

    private void init() {
        redPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        redPaint.setStyle(Paint.Style.STROKE);
        redPaint.setColor(0xffff0000);
        redPaint.setStrokeWidth(5);

        greenPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        greenPaint.setStyle(Paint.Style.STROKE);
        greenPaint.setARGB(255, 0, 255, 0);
        greenPaint.setStrokeWidth(5);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawRect(10, 30, 200, 200, redPaint);
        canvas.drawCircle(300, 300, 250, redPaint);

        mylines.moveTo(0, 0);
        mylines.lineTo(200, 50);
        mylines.lineTo(300, 150);
        mylines.lineTo(400, 250);
        mylines.lineTo(500, 300);

        canvas.drawPath(mylines, greenPaint);

    }
}

这里是显示器。 （我为该视图的可见性添加了灰色背景，但这不是必需的。）