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 doesn't mean that the reference point of the text is vertically centered. The reference point is always on the baseline. So, why not use Paint.Align.LEFT? You have to calculate the reference point anyway.
Paint.descent() has the disadvantage, that it doesn't consider the real text. Paint.descent() retrieves the same value, regardless of whether the text contains letters with descents or not. That's why I use r.bottom instead.
I have had some problems with Canvas.getHeight() if API < 16. That's why I use Canvas.getClipBounds(Rect) instead. (Do not use Canvas.getClipBounds().getHeight() as it allocates memory for a Rect.)
For reasons of performance, you should allocate objects before they are used in onDraw(). As drawCenter() will be called within onDraw() the object Rect r is preallocated as a field here.
我尝试把上面两个答案的代码放到我自己的代码中(2015年8月)，并做了一个截图来对比结果:
文本应该在红色填充矩形内居中。我的代码生成白色文本，其他两个代码生成灰色文本(它们实际上是相同的，重叠的)。灰色的文字有点太低了，右边多了两个。
我是这样做测试的:
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);
}
}
