java - 画布上的 Android 中心文本

Question

我正在尝试使用下面的代码显示文本。问题是文本没有水平居中。当我为设置坐标时drawText，它将文本的底部设置在此位置。我希望绘制文本，以便文本也水平居中。

这是一张进一步显示我的问题的图片：

@Override
protected void onDraw(Canvas canvas) {
    // TODO Auto-generated method stub
    super.onDraw(canvas);
    //canvas.drawRGB(2, 2, 200);
    Paint textPaint = new Paint();
    textPaint.setARGB(200, 254, 0, 0);
    textPaint.setTextAlign(Align.CENTER);
    textPaint.setTypeface(font);
    textPaint.setTextSize(300);
    canvas.drawText("Hello", canvas.getWidth()/2, canvas.getHeight()/2  , textPaint);
}

score 408 · Accepted Answer

尝试以下操作：

 Paint textPaint = new Paint();
 textPaint.setTextAlign(Paint.Align.CENTER);

 int xPos = (canvas.getWidth() / 2);
 int yPos = (int) ((canvas.getHeight() / 2) - ((textPaint.descent() + textPaint.ascent()) / 2)) ; 
 //((textPaint.descent() + textPaint.ascent()) / 2) is the distance from the baseline to the center.

 canvas.drawText("Hello", xPos, yPos, textPaint);

score 244 · Accepted Answer

以Paint.getTextBounds() 居中：

private Rect r = new Rect();

private void drawCenter(Canvas canvas, Paint paint, String text) {
    canvas.getClipBounds(r);
    int cHeight = r.height();
    int cWidth = r.width();
    paint.setTextAlign(Paint.Align.LEFT);
    paint.getTextBounds(text, 0, text.length(), r);
    float x = cWidth / 2f - r.width() / 2f - r.left;
    float y = cHeight / 2f + r.height() / 2f - r.bottom;
    canvas.drawText(text, x, y, paint);
}

Paint.Align.CENTER并不意味着文本的参考点垂直居中。参考点始终位于基线上。那么，为什么不使用Paint.Align.LEFT呢？无论如何，您必须计算参考点。
Paint.descent()的缺点是它不考虑真实的文本。Paint.descent()检索相同的值，无论文本是否包含带血统的字母。这就是我使用r.bottom的原因。
如果 API < 16，我在使用Canvas.getHeight ()时遇到了一些问题。这就是我改用Canvas.getClipBounds(Rect)的原因。（不要使用Canvas.getClipBounds().getHeight()因为它为Rect分配内存。）
出于性能原因，您应该在使用onDraw()之前分配对象。因为drawCenter()将在onDraw()中被调用，所以对象Rect r在这里被预分配为一个字段。

我尝试将两个热门答案的代码放入我自己的代码中（2015 年 8 月），并制作了一个屏幕截图来比较结果：

文本应该在红色填充的矩形内居中。我的代码生成白色文本，其他两个代码完全生成灰色文本（它们实际上是相同的，重叠的）。灰色文本有点太低了，右边有两个。

这就是我进行测试的方式：

import android.app.Activity;
import android.content.Context;
import android.content.pm.ActivityInfo;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.RectF;
import android.graphics.Typeface;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;

class MyView extends View {

    private static String LABEL = "long";
    private static float TEXT_HEIGHT_RATIO = 0.82f;

    private FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(0, 0);
    private Rect r = new Rect();
    private Paint paint = new Paint();
    private Paint rectPaint = new Paint();

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

    private void drawTextBounds(Canvas canvas, Rect rect, int x, int y) {
        rectPaint.setColor(Color.rgb(0, 0, 0));
        rectPaint.setStyle(Paint.Style.STROKE);
        rectPaint.setStrokeWidth(3f);
        rect.offset(x, y);
        canvas.drawRect(rect, rectPaint);
    }

    // andreas1724 (white color):
    private void draw1(Canvas canvas, Paint paint, String text) {
        paint.setTextAlign(Paint.Align.LEFT);
        paint.setColor(Color.rgb(255, 255, 255));
        canvas.getClipBounds(r);
        int cHeight = r.height();
        int cWidth = r.width();
        paint.getTextBounds(text, 0, text.length(), r);
        float x = cWidth / 2f - r.width() / 2f - r.left;
        float y = cHeight / 2f + r.height() / 2f - r.bottom;
        canvas.drawText(text, x, y, paint);
        drawTextBounds(canvas, r, (int) x, (int) y);
    }

    // Arun George (light green color):
    private void draw2(Canvas canvas, Paint textPaint, String text) {
        textPaint.setTextAlign(Paint.Align.CENTER);
        textPaint.setColor(Color.argb(100, 0, 255, 0));
        int xPos = (canvas.getWidth() / 2);
        int yPos = (int) ((canvas.getHeight() / 2) - ((textPaint.descent() + textPaint.ascent()) / 2));
        canvas.drawText(text, xPos, yPos, textPaint);
    }

    // VinceStyling (light blue color):
    private void draw3(Canvas yourCanvas, Paint mPaint, String pageTitle) {
        mPaint.setTextAlign(Paint.Align.LEFT);
        mPaint.setColor(Color.argb(100, 0, 0, 255));
        r = yourCanvas.getClipBounds();
        RectF bounds = new RectF(r);
        bounds.right = mPaint.measureText(pageTitle, 0, pageTitle.length());
        bounds.bottom = mPaint.descent() - mPaint.ascent();
        bounds.left += (r.width() - bounds.right) / 2.0f;
        bounds.top += (r.height() - bounds.bottom) / 2.0f;
        yourCanvas.drawText(pageTitle, bounds.left, bounds.top - mPaint.ascent(), mPaint);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        int margin = 10;
        int width = w - 2 * margin;
        int height = h - 2 * margin;
        params.width = width;
        params.height = height;
        params.leftMargin = margin;
        params.topMargin = margin;
        setLayoutParams(params);
        paint.setTextSize(height * TEXT_HEIGHT_RATIO);
        paint.setAntiAlias(true);
        paint.setTypeface(Typeface.create(Typeface.SERIF, Typeface.BOLD_ITALIC));
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(Color.rgb(255, 0, 0));
        draw1(canvas, paint, LABEL);
        draw2(canvas, paint, LABEL);
        draw3(canvas, paint, LABEL);
    }
}

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRequestedOrientation (ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
        FrameLayout container = new FrameLayout(this);
        container.setLayoutParams(new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT,
                ViewGroup.LayoutParams.MATCH_PARENT));
        container.addView(new MyView(this));
        setContentView(container);
    }
}

score 67 · Accepted Answer

垂直对齐很困难，因为发生了文本下降和上升，很多人使用Paint.getTextBounds()来检索 TextWidth 和 TextHeight，但它并没有使文本居中。这里我们可以使用Paint.measureText()来计算TextWidth，TextHeight我们简单的用descent和ascent做减法，然后我们得到最接近的TextSize，下面的工作互相比较容易。

// the Paint instance(should be assign as a field of class).
Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setTextSize(getResources().getDimension(R.dimen.btn_textsize));

// the display area.
Rect areaRect = new Rect(0, 0, 240, 60);

// draw the background style (pure color or image)
mPaint.setColor(Color.BLACK);
yourCanvas.drawRect(areaRect, mPaint);

String pageTitle = "文字小说";

RectF bounds = new RectF(areaRect);
// measure text width
bounds.right = mPaint.measureText(pageTitle, 0, pageTitle.length());
// measure text height
bounds.bottom = mPaint.descent() - mPaint.ascent();

bounds.left += (areaRect.width() - bounds.right) / 2.0f;
bounds.top += (areaRect.height() - bounds.bottom) / 2.0f;

mPaint.setColor(Color.WHITE);
yourCanvas.drawText(pageTitle, bounds.left, bounds.top - mPaint.ascent(), mPaint);

代码截图

顺便说一句，我们强烈建议使用RectF而不是Rect，因为位置需要更准确的值，根据我的经验，RectF 在 xhdpi 设备上只完成了一个像素的上下偏差，而 Rect 会多两个。

score 17 · Accepted Answer

您的代码在视图中心绘制文本基线的中心。为了使文本在某个点 x、y 居中，您需要计算文本的中心，并将其放在该点上。

此方法将以点 x、y 为中心绘制文本。如果您将它传递到视图的中心，它将居中绘制文本。

private void drawTextCentered(String text, int x, int y, Paint paint, Canvas canvas) {
    int xPos = x - (int)(paint.measureText(text)/2);
    int yPos = (int) (y - ((textPaint.descent() + textPaint.ascent()) / 2)) ;

    canvas.drawText(text, xPos, yPos, textPaint);
}

score 4 · Accepted Answer

我发现居中文本的最佳解决方案如下：

textPaint.setTextAlign(Paint.Align.CENTER);
//textPaint is the Paint object being used to draw the text (it must be initialized beforehand)
float textY=center.y;
float textX=center.x; 
// in this case, center.x and center.y represent the coordinates of the center of the rectangle in which the text is being placed
canvas.drawText(text,textX,textY,textPaint);    `

score 3 · Accepted Answer

适合我使用： textPaint.textAlign = Paint.Align.CENTER with textPaint.getTextBounds

private fun drawNumber(i: Int, canvas: Canvas, translate: Float) {
            val text = "$i"
            textPaint.textAlign = Paint.Align.CENTER
            textPaint.getTextBounds(text, 0, text.length, textBound)

            canvas.drawText(
                    "$i",
                    translate + circleRadius,
                    (height / 2 + textBound.height() / 2).toFloat(),
                    textPaint
            )
        }

结果是：

score 2 · Accepted Answer

这对我有用：

 paint.setTextAlign(Paint.Align.CENTER);
        int xPos = (newWidth / 2);
        int yPos = (newHeight / 2);
        canvas.drawText("Hello", xPos, yPos, paint);

如果有人发现任何问题，请告诉我

score 2 · Accepted Answer

将这些添加到您的 onDraw 方法中：

paint.setColor(getContext().getResources().getColor(R.color.black));
paint.setTextAlign(Paint.Align.CENTER);
canvas.drawText("Text", (float) getHeight() / 2f, (float) getWidth() / 2f, paint);

score 1 · Accepted Answer

我创建了一个方法来简化这个：

    public static void drawCenterText(String text, RectF rectF, Canvas canvas, Paint paint) {
    Paint.Align align = paint.getTextAlign();
    float x;
    float y;
    //x
    if (align == Paint.Align.LEFT) {
        x = rectF.centerX() - paint.measureText(text) / 2;
    } else if (align == Paint.Align.CENTER) {
        x = rectF.centerX();
    } else {
        x = rectF.centerX() + paint.measureText(text) / 2;
    }
    //y
    metrics = paint.getFontMetrics();
    float acent = Math.abs(metrics.ascent);
    float descent = Math.abs(metrics.descent);
    y = rectF.centerY() + (acent - descent) / 2f;
    canvas.drawText(text, x, y, paint);

    Log.e("ghui", "top:" + metrics.top + ",ascent:" + metrics.ascent
            + ",dscent:" + metrics.descent + ",leading:" + metrics.leading + ",bottom" + metrics.bottom);
}

rectF就是你要绘制文字的区域，就是这样。细节

score 1 · Accepted Answer

就我而言，我不必将文本放在画布中间，而是放在一个旋转的轮子中。尽管我必须使用此代码才能成功：

fun getTextRect(textSize: Float, textPaint: TextPaint, string: String) : PointF {
    val rect = RectF(left, top, right, bottom)
    val rectHeight = Rect()
    val cx = rect.centerX()
    val cy = rect.centerY()

    textPaint.getTextBounds(string, 0, string.length, rectHeight)
    val y = cy + rectHeight.height()/2
    val x = cx - textPaint.measureText(string)/2

    return PointF(x, y)
}

然后我从 View 类中调用这个方法：

private fun drawText(canvas: Canvas, paint: TextPaint, text: String, string: String) {
    val pointF = getTextRect(paint.textSize, textPaint, string)
    canvas.drawText(text, pointF!!.x, pointF.y, paint)
}

score 1 · Accepted Answer

1

在您的油漆属性中使用它：

 textPaint.setTextAlign(Paint.Align.CENTER);

于 2020-10-01T07:21:42.290 回答

score 0 · Accepted Answer

如果我们使用静态布局

mStaticLayout = new StaticLayout(mText, mTextPaint, mTextWidth,
                Layout.Alignment.ALIGN_CENTER, 1.0f, 0, true);

Layout.Alignment.ALIGN_CENTER这可以解决问题。静态布局还有很多其他优点。

参考：Android 文档

java - 画布上的 Android 中心文本

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