How are you supposed to use a ShapeDrawable with a

问题:

I am attempting to draw a line in a custom View. Here I've created a simple Path with just a single segment, created a PathShape from that, and finally stuck that into a ShapeDrawable with the intention of using that to draw on the Canvas inside onDraw(). However, this does not work. See my example, here.

package com.example.test;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.PathShape;
import android.util.Log;
import android.view.View;

public class TestView extends View {

    private Path mPath = null;
    private Paint mPaint = null;
    private PathShape mPathShape = null;
    private ShapeDrawable mShapeDrawable = null;

    public TestView(Context context) {
        super(context);
    }

    private void init() {
        int width = this.getWidth() / 2;
        int height = this.getHeight() / 2;

        Log.d("init", String.format("width: %d; height: %d", width, height));

        this.mPath = new Path();
        this.mPath.moveTo(0, 0);
        this.mPath.lineTo(width, height);

        this.mPaint = new Paint();
        this.mPaint.setColor(Color.RED);

        this.mPathShape = new PathShape(this.mPath, 1, 1);

        this.mShapeDrawable = new ShapeDrawable(this.mPathShape);
        this.mShapeDrawable.getPaint().set(this.mPaint);
        this.mShapeDrawable.setBounds(0, 0, width, height);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);

        // Doing this here because in the constructor we don't have the width and height of the view, yet
        this.init();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        Log.d("onDraw", "Drawing");

        // This works, but won't let me do what I'm really trying to do
        canvas.drawLine(0.0f, 0.0f, this.getWidth() / 2.0f, this.getHeight() / 2.0f, this.mPaint);

        // This should work, but does not
        //this.mPathShape.draw(canvas, this.mPaint);

        // This should work, but does not
        //this.mShapeDrawable.draw(canvas);
    }

}

As you can see from my comments in the onDraw() method, neither using the PathShape nor the ShapeDrawable to draw the Path onto the Canvas actually works. Nothing is drawn when I try. Does anyone have any idea why?

The device I'm testing this on is running Android 4.1.1.

回答1:

There are two issues with this.

The first is the Paint style. The default is Paint.Stroke.FILL, but with a line there's nothing to fill. I needed to add this (thanks, Romain Guy):

this.mPaint.setStyle(Paint.Style.STROKE);

The second issue is that the standard height and width in the PathShape is not correct. I had read the documentation on this, but did not understand it correctly. This became apparent once I fixed the first issue. Setting it to the height and width of my custom view (since I am drawing across the whole view) fixed this. I also had to change the bounds of the ShapeDrawable to match.

this.mPathShape = new PathShape(this.mPath, this.getWidth(), this.getHeight());

and

this.mShapeDrawable.setBounds(0, 0, this.getWidth(), this.getHeight());

Hopefully this helps someone else in the future.