如何将文本放入可绘制对象中？

Question

我正在尝试动态创建一个可绘制对象以用作自定义线性布局的背景。它需要有哈希标记等（没什么大不了的），但也有数字标记哈希标记是什么（如尺子）。我知道我可以创建文本元素并将它们放在线性布局中，并在可绘制对象中添加散列标记，但我希望将它们也包含在可绘制对象中，因此我不必进行两次测量计算。

Answer 1

这里是一个TextDrawable 的简短示例，它的工作方式类似于普通的可绘制对象，但允许您将文本指定为唯一的构造函数变量：

public class TextDrawable extends Drawable {

    private final String text;
    private final Paint paint;

    public TextDrawable(String text) {

        this.text = text;

        this.paint = new Paint();
        paint.setColor(Color.WHITE);
        paint.setTextSize(22f);
        paint.setAntiAlias(true);
        paint.setFakeBoldText(true);
        paint.setShadowLayer(6f, 0, 0, Color.BLACK);
        paint.setStyle(Paint.Style.FILL);
        paint.setTextAlign(Paint.Align.LEFT);
    }

    @Override
    public void draw(Canvas canvas) {
        canvas.drawText(text, 0, 0, paint);
    }

    @Override
    public void setAlpha(int alpha) {
        paint.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(ColorFilter cf) {
        paint.setColorFilter(cf);
    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }
}

Answer 2

我读过“Professional Android 2 Application Development”一书（Reto Meier 着）。其中，它包含一个示例项目，您可以在其中创建一个简单的指南针应用程序，您可以在其中“绘制”文本、标记等。

简单的解释是你创建了一个扩展android.view.View类并覆盖onDraw(Canvas)方法的类。

本书的所有源代码都可以在这里下载：http://www.wrox.com/WileyCDA/WroxTitle/Professional-Android-2-Application-Development.productCd-0470565527,descCd-DOWNLOAD.html。如果你下载代码并查看名为“Chapter 4 Compass”的项目，我相信你会找到你想要的:)

Answer 3

看着 Plowman 的回答并试图根据我的需要调整它，我偶然发现了一个用于 Camera in this link 的类

这是来自TextDrawable Class 的代码。看起来与 Plowmans 很相似，但对我来说效果更好：

import android.content.res.Resources;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.Paint.Align;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.TypedValue;

public class TextDrawable extends Drawable {
    private static final int DEFAULT_COLOR = Color.WHITE;
    private static final int DEFAULT_TEXTSIZE = 15;
    private Paint mPaint;
    private CharSequence mText;
    private int mIntrinsicWidth;
    private int mIntrinsicHeight;

    public TextDrawable(Resources res, CharSequence text) {
        mText = text;
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(DEFAULT_COLOR);
        mPaint.setTextAlign(Align.CENTER);
        float textSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP,
                DEFAULT_TEXTSIZE, res.getDisplayMetrics());
        mPaint.setTextSize(textSize);
        mIntrinsicWidth = (int) (mPaint.measureText(mText, 0, mText.length()) + .5);
        mIntrinsicHeight = mPaint.getFontMetricsInt(null);
    }
    @Override
    public void draw(Canvas canvas) {
        Rect bounds = getBounds();
        canvas.drawText(mText, 0, mText.length(),
                bounds.centerX(), bounds.centerY(), mPaint);
    }
    @Override
    public int getOpacity() {
        return mPaint.getAlpha();
    }
    @Override
    public int getIntrinsicWidth() {
        return mIntrinsicWidth;
    }
    @Override
    public int getIntrinsicHeight() {
        return mIntrinsicHeight;
    }
    @Override
    public void setAlpha(int alpha) {
        mPaint.setAlpha(alpha);
    }
    @Override
    public void setColorFilter(ColorFilter filter) {
        mPaint.setColorFilter(filter);
    }
}

Answer 4

回答上面关于如何使文本居中的问题：

mPaint.textAlign = Align.CENTER
...
// Centering for mixed case letters
canvas.drawText(mText, 0, mText.length,
        bounds.centerX().toFloat(), bounds.centerY().toFloat() - ((mPaint.descent() + mPaint.ascent()) / 2), mPaint)

// Centering for all uppercase letters
canvas.drawText(mText, 0, mText.length,
            bounds.centerX().toFloat(), bounds.centerY().toFloat() - mPaint.ascent() / 2, mPaint)

Answer 5

这允许您将任何 View 放入 Drawable，包括 TextView。您甚至可以在 XML 布局中使用样式。

public class ViewDrawable extends Drawable {
    final View mView;

    public ViewDrawable(final Context context, final @LayoutRes int layoutId) {
        this(LayoutInflater.from(context).inflate(layoutId, null));
    }

    public ViewDrawable(final @NonNull View view) {
        mView = view;
    }

    public View getView() {
        return mView;
    }

    @Override
    public void setBounds(int left, int top, int right, int bottom) {
        super.setBounds(left, top, right, bottom);
        final int widthMeasureSpec = View.MeasureSpec.makeMeasureSpec(right - left, View.MeasureSpec.EXACTLY);
        final int heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(bottom - top, View.MeasureSpec.EXACTLY);
        mView.measure(widthMeasureSpec, heightMeasureSpec);
        mView.layout(left, top, right, bottom);
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        mView.draw(canvas);
    }

    @Override
    public void setAlpha(int alpha) {
        mView.setAlpha(alpha/255f);
    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {

    }

    @Override
    public int getOpacity() {
        return PixelFormat.UNKNOWN;
    }
}