Android 画布.drawText

Question

我有一个视图，在onDraw(Canvas canvas)方法中使用Canvas对象进行绘制。我的代码如下：

Paint paint = new Paint();
paint.setColor(Color.WHITE);
paint.setStyle(Style.FILL);
canvas.drawPaint(paint);

paint.setColor(android.R.color.black);
paint.setTextSize(20);
canvas.drawText("Some Text", 10, 25, paint);

问题是文字不能透过背景显示，我做错了什么？如果我移除canvas.drawPaint（paint）和paint.setColor（android.R.color.black），你就可以在屏幕上看到文字.....

- Gaz

Answer 1

我已经解决了这个问题，原来android.R.color.black与Color.BLACK并不相同，所以将代码更改为：

Paint paint = new Paint(); 
paint.setColor(Color.WHITE); 
paint.setStyle(Style.FILL); 
canvas.drawPaint(paint); 

paint.setColor(Color.BLACK); 
paint.setTextSize(20); 
canvas.drawText("Some Text", 10, 25, paint); 

现在一切都正常工作了！！

- Gaz

---

如果您想在res/colors.xml文件中使用ID为R.color.black的颜色定义，则不能仅使用该ID。如果您想从资源中获取实际颜色值，请使用paint.setColor(getResources().getColor(R.color.black));。 - Matt Gibson

有人知道如何在Android Canvas ShapeDrawable中使用RectShape绘制文本吗？ - LOG_TAG

而要设置文本大小为“dp”，您可以使用此链接中的方法。 - S.M.Mousavi

重置样式为“填充”非常重要，否则它可能会描边您的文本（可能使用非常粗的线条），看起来非常粗糙和丑陋。 - Chase Roberts

在 drawText("一些文本", 10, 25, paint); 中，它意味着左边距为10，顶部边距为25。我说得对吗？ - Prince Dholakiya

@PrinceDholakiya 那是 x 和 y.. 表示文本的左上角位置。 - glennmark

Answer 2

需要注意的是，文档建议使用 Layout 而不是直接使用 Canvas.drawText。我在这里提供有关使用 StaticLayout 的完整答案此处，但我会在下面提供摘要。

String text = "This is some text.";

TextPaint textPaint = new TextPaint();
textPaint.setAntiAlias(true);
textPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
textPaint.setColor(0xFF000000);

int width = (int) textPaint.measureText(text);
StaticLayout staticLayout = new StaticLayout(text, textPaint, (int) width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);
staticLayout.draw(canvas);

这里是一个在自定义视图上下文中的更完整的示例：

public class MyView extends View {

    String mText = "This is some text.";
    TextPaint mTextPaint;
    StaticLayout mStaticLayout;

    // use this constructor if creating MyView programmatically
    public MyView(Context context) {
        super(context);
        initLabelView();
    }

    // this constructor is used when created from xml
    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initLabelView();
    }

    private void initLabelView() {
        mTextPaint = new TextPaint();
        mTextPaint.setAntiAlias(true);
        mTextPaint.setTextSize(16 * getResources().getDisplayMetrics().density);
        mTextPaint.setColor(0xFF000000);

        // default to a single line of text
        int width = (int) mTextPaint.measureText(mText);
        mStaticLayout = new StaticLayout(mText, mTextPaint, (int) width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);

        // New API alternate
        //
        // StaticLayout.Builder builder = StaticLayout.Builder.obtain(mText, 0, mText.length(), mTextPaint, width)
        //        .setAlignment(Layout.Alignment.ALIGN_NORMAL)
        //        .setLineSpacing(1, 0) // multiplier, add
        //        .setIncludePad(false);
        // mStaticLayout = builder.build();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // Tell the parent layout how big this view would like to be
        // but still respect any requirements (measure specs) that are passed down.

        // determine the width
        int width;
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthRequirement = MeasureSpec.getSize(widthMeasureSpec);
        if (widthMode == MeasureSpec.EXACTLY) {
            width = widthRequirement;
        } else {
            width = mStaticLayout.getWidth() + getPaddingLeft() + getPaddingRight();
            if (widthMode == MeasureSpec.AT_MOST) {
                if (width > widthRequirement) {
                    width = widthRequirement;
                    // too long for a single line so relayout as multiline
                    mStaticLayout = new StaticLayout(mText, mTextPaint, width, Layout.Alignment.ALIGN_NORMAL, 1.0f, 0, false);
                }
            }
        }

        // determine the height
        int height;
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightRequirement = MeasureSpec.getSize(heightMeasureSpec);
        if (heightMode == MeasureSpec.EXACTLY) {
            height = heightRequirement;
        } else {
            height = mStaticLayout.getHeight() + getPaddingTop() + getPaddingBottom();
            if (heightMode == MeasureSpec.AT_MOST) {
                height = Math.min(height, heightRequirement);
            }
        }

        // Required call: set width and height
        setMeasuredDimension(width, height);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // do as little as possible inside onDraw to improve performance

        // draw the text on the canvas after adjusting for padding
        canvas.save();
        canvas.translate(getPaddingLeft(), getPaddingTop());
        mStaticLayout.draw(canvas);
        canvas.restore();
    }
}

- Suragch