文字尺寸、寬高的測量 Paint FontMetrics

Paint.FontMetrics類簡介

Google文檔中的描 述：

/**
   
   
   
           
 * Class that describes the various各種 metrics指標 for a font at a given text size.
 * Remember, Y values increase going down, so those values will be positive正數,
 * and values that measure distances距離 going up will be negative負數. This class
 * is returned by getFontMetrics().
 */
public static class FontMetrics {
 //The maximum distance above the baseline for the tallest glyph in the font at a given text size.
 public float top;
 //【字符頂部】The recommended推薦的 distance above the baseline for singled spaced text.
 public float ascent;
 //【字符底部】The recommended distance below the baseline for singled spaced text.
 public float descent;
 //The maximum distance below the baseline for the lowest glyph in the font at a given text size.
 public float bottom;
 //【字符行間距】The recommended additional額外的 space to add between lines兩行之間 of text.
 public float leading;
}

網上找的各種模型圖

注意Y坐標基准點是在BaseLine那個位置，而非AscentLine或Top那個位置

Paint的ascent和descent方法--算高度

這兩個是native方法

//Return the distance above (negative) the baseline (ascent) based on the current typeface字體 and text size.
public native float ascent();
//Return the distance below (positive) the baseline (descent) based on the current typeface and text size.
public native float descent();

可以通過 mPaint.ascent()+ mPaint.descent() 獲取文字高度

Paint的measureText方法--獲取寬度

/**
 * Return the width of the text.
 *
 * @param text The text to measure. Cannot be null.
 * @param start The index of the first character to start measuring
 * @param end 1 beyond the index of the last character to measure
 * @return The width of the text
 */
public float measureText(String text, int start, int end) {
 if (text == null) throw new IllegalArgumentException("text cannot be null");
 if ((start | end | (end - start) | (text.length() - end)) < 0) throw new IndexOutOfBoundsException();
 if (text.length() == 0 || start == end) return 0f;
 if (!mHasCompatScaling) return (float) Math.ceil(native_measureText(text, start, end, mBidiFlags));

 final float oldSize = getTextSize();
 setTextSize(oldSize*mCompatScaling);
 float w = native_measureText(text, start, end, mBidiFlags);
 setTextSize(oldSize);
 return (float) Math.ceil(w*mInvCompatScaling);
}

通過這個方法即可以輕松的獲取到文字的的寬度

Paint的getTextBounds方法--獲取邊界

/**
 * Return in bounds (allocated by the caller 由調用者分配) the smallest最小的 rectangle that
 * encloses圍起來 all of the characters, with an implied origin默認的起始位置 at (0,0).
 * @param text String to measure and return its bounds
 * @param start Index of the first char in the string to measure
 * @param end 1 past the last char in the string measure
 * @param bounds Returns the unioned bounds of all the text. Must be allocated by the caller.
 */
public void getTextBounds(String text, int start, int end, Rect bounds) {
 if ((start | end | (end - start) | (text.length() - end)) < 0)  throw new IndexOutOfBoundsException();
 if (bounds == null) throw new NullPointerException("need bounds Rect");
 nativeGetStringBounds(mNativePaint, mNativeTypeface, text, start, end, mBidiFlags, bounds);
}

這個方法需要提供一個參數 Rect 矩形區域，這個方法將文字的區域傳遞到 Rect

Paint的獲取

比如對於TextView，要通過 TextView的 getPaint()得到 Paint，而不能new一個或者拿其他不相干的 Paint

/**
 * @return the base paint used for the text. Please use this only to
 * consult查閱 the Paint's properties屬性 and not to change them.
 */
public TextPaint getPaint() {
 return mTextPaint;
}

如果是在自定義View 中，則可以 直接 通過Paint調用相關方法去獲取文字的寬高等信息

測試代碼

public class MainActivity extends Activity {

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        String text = "aA bB fF gG";

        TextView tv_info = new TextView(this);

        tv_info.setTextColor(Color.BLUE);

        tv_info.setBackgroundColor(0x5500ff00);

        tv_info.setTextSize(TypedValue.COMPLEX_UNIT_SP, 18);

        tv_info.setText(text);

        setContentView(tv_info);

        tv_info.measure(0, 0);//必須手動調用測量方法，否則getMeasuredHeight獲取不到值。另外，即使測量過了getHeight也獲取不到值

        Paint mPaint = tv_info.getPaint();

        Log.i("bqt", "ascent()的值為" + mPaint.ascent() + "，descent()的值為" + mPaint.descent());//-33.398438， 8.7890625

        Log.i("bqt", "字符的高度為" + (-mPaint.ascent() + mPaint.descent()) + "，字符的長度為" + mPaint.measureText(text));//42.1875，190.0

        Log.i("bqt", "測量的高度為" + tv_info.getMeasuredHeight() + "，測量的寬度為" + tv_info.getMeasuredWidth());//49，190

        Rect mRect = new Rect();

        mPaint.getTextBounds(text, 0, text.length(), mRect);

        Log.i("bqt", "字符的邊界為" + mRect.left + "，" + mRect.top + "，" + mRect.right + "，" + mRect.bottom);//1，-28，187，8

        Log.i("bqt", "字符的高度為" + (mRect.bottom - mRect.top) + "，字符的長度為" + (mRect.right - mRect.left));//36，186

    }

}