Android中如何使用StaticLayout？

Question

我需要构建自己的自定义 TextView，所以我一直在学习 StaticLayout 在画布上绘制文本。这比直接使用Canvas.drawText() 更好，或者documentation 这么说。但是，该文档没有给出如何做到这一点的任何示例。只是模糊地提到 StaticLayout.Builder 是更新的方法。

我找到了一个示例 here，但它似乎有点过时了。

我终于知道怎么做，所以我在下面添加我的解释。

Answer 1

StaticLayout (similar to DynamicLayout and BoringLayout) 用于在画布上布局和绘制文本。它通常用于以下任务：

• 测量多行文本布局后的大小。
• 在位图图像上绘制文本。
• 制作处理其自己的文本布局的自定义视图（与使用嵌入的TextView 制作复合视图相反）。 TextView 本身使用 StaticLayout internally。

测量文字大小

单行

如果你只有一行文字，你可以用Paint或TextPaint来衡量它。

String text = "This is some text."

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

float width = mTextPaint.measureText(text);
float height = -mTextPaint.ascent() + mTextPaint.descent();

多行

但是，如果有换行并且您需要高度，那么最好使用StaticLayout。您提供宽度，然后您可以从StaticLayout 获取高度。

String text = "This is some text. This is some text. This is some text. This is some text. This is some text. This is some text.";

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

int width = 200;
Layout.Alignment alignment = Layout.Alignment.ALIGN_NORMAL;
float spacingMultiplier = 1;
float spacingAddition = 0;
boolean includePadding = false;

StaticLayout myStaticLayout = new StaticLayout(text, myTextPaint, width, alignment, spacingMultiplier, spacingAddition, includePadding);

float height = myStaticLayout.getHeight(); 

新 API

如果您想使用较新的 StaticLayout.Builder（可从 API 23 获得），您可以像这样获得布局：

StaticLayout.Builder builder = StaticLayout.Builder.obtain(text, 0, text.length(), myTextPaint, width);
StaticLayout myStaticLayout = builder.build();

您可以使用点表示法添加附加设置：

StaticLayout.Builder builder = StaticLayout.Builder.obtain(text, 0, text.length(), myTextPaint, width)
        .setAlignment(Layout.Alignment.ALIGN_NORMAL)
        .setLineSpacing(spacingAddition, spacingMultiplier)
        .setIncludePad(includePadding)
        .setMaxLines(5);
StaticLayout myStaticLayout = builder.build();

在图像上书写文字

我将来可能会对此进行更多扩展，但现在请参阅 this post 以获取使用 StaticLayout 并返回位图的方法示例。

制作自定义文本处理视图

这是一个使用StaticLayout 的自定义视图示例。它的行为就像一个简单的TextView。当文本太长而无法在屏幕上显示时，它会自动换行并增加其高度。

代码

MyView.java

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(0, 1) // add, multiplier
        //        .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();
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="@dimen/activity_vertical_margin"
    tools:context="com.example.layoutpractice.MainActivity">

    <com.example.layoutpractice.MyView
        android:layout_centerHorizontal="true"
        android:background="@color/colorAccent"
        android:padding="10dp"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</RelativeLayout>

备注

• This、this 和 this 在学习如何制作自定义文本处理视图时非常有用。

• 如果您想添加可以从代码或 xml 设置的自定义属性，请参阅 Creating a View Class。

Answer 2

这是我在画布上绘制多行文本的解释。

声明 Paint 对象。使用 TextPaint，它是 Paint 的扩展。

TextPaint textPaint;

初始化 Paint 对象。设置自己的颜色、大小等。

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

添加getTextHeight函数

private float getTextHeight(String text, Paint paint) {
    Rect rect = new Rect();
    paint.getTextBounds(text, 0, text.length(), rect);
    return rect.height();
}

在你的 onDraw 函数中加入如下几行

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    String text = "This is a lengthy text. We have to render this properly. If layout mess users review will mess. Is that so ? ";

    Rect bounds = canvas.getClipBounds();

    StaticLayout sl = new StaticLayout(text, textPaint, bounds.width(),
            Layout.Alignment.ALIGN_CENTER, 1, 1, true);

    canvas.save();

    //calculate X and Y coordinates - In this case we want to draw the text in the
    //center of canvas so we calculate
    //text height and number of lines to move Y coordinate to center.
    float textHeight = getTextHeight(text, textPaint);
    int numberOfTextLines = sl.getLineCount();
    float textYCoordinate = bounds.exactCenterY() -
            ((numberOfTextLines * textHeight) / 2);

    //text will be drawn from left
    float textXCoordinate = bounds.left;

    canvas.translate(textXCoordinate, textYCoordinate);

    //draws static layout on canvas
    sl.draw(canvas);
    canvas.restore();
}

感谢KOC's post