How to create vertically aligned superscript and subscript in TextView

问题

In the example of image below:

How can I make both the superscript and subscript numbers to be aligned to produce a common scientific notation like below

in TextView? If there is a way using Spannable or ReplacementSpan I would like to see a working example. Thank you.

回答1:

You might want to try something like this.

It's basicall a ReplacementSpan that takes the text it's applied on, separates it into two parts, and draws them on the canvas. The size factor and y translation are somewhat hand-picked. I hope it's useful (or at least that you or someone else can build on it).

public class SuperSubSpan extends ReplacementSpan
{
    @Override
    public int getSize(Paint paint, CharSequence text, int start, int end, FontMetricsInt fm)
    {
        text = text.subSequence(start, end);
        String[] parts = text.toString().split(",");

        Paint p = getSuperSubPaint(paint);
        return (int) Math.max(p.measureText(parts[0]), p.measureText(parts[1]));
    }

    private static TextPaint getSuperSubPaint(Paint src)
    {
        TextPaint paint = new TextPaint(src);
        paint.setTextSize(src.getTextSize() / 2.5f);
        return paint;
    }

    @Override
    public void draw(Canvas canvas, CharSequence text, int start, int end, float x, int top, int y, int bottom, Paint paint)
    {
        text = text.subSequence(start, end);
        String[] parts = text.toString().split(",");

        Paint p = getSuperSubPaint(paint);

        float width1 = p.measureText(parts[0]);
        float width2 = p.measureText(parts[1]);
        float maxWidth = Math.max(width1, width2);

        canvas.drawText(parts[0], x + (maxWidth - width1), y - (bottom - top) / 3f, p);
        canvas.drawText(parts[1], x + (maxWidth - width2), y + (bottom - top) / 10f, p);
    }
}

Then use it as:

Spannable str = new SpannableString("9,4Be -> 2000,127Jo");
str.setSpan(new SuperSubSpan(), 0, 3, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
str.setSpan(new SuperSubSpan(), 9, 17, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
mTextView.setText(str);

which produces the following result:

A slightly better solution would be to have a special format for these strings (e.g. "{9,4}Be -> {2000,127}Jo") and have a regular expression process the string and add the corresponding SuperSubSpans, just so that you don't need to this manually. But the actual Span part would be more or less the same.

回答2:

If you just want subscript and superscript, use SubscriptSpannable and SuperscriptSpannable. If you don't like how those draw out for some reason, you can always make a custom spannable and draw it yourself.

回答3:

use this code for solution....

TextView txt = (TextView)findViewById(R.id.txt_label); txt.setText(Html.fromHtml("<sup>9</sup><sub>4</sub>Be"));

回答4:

you can follow me step by step. You get help from this. such as

MainActivity.java

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView txtView = (TextView) findViewById(R.id.textView1);
        TextView water = (TextView) findViewById(R.id.textView2);
        txtView.setText(Html.fromHtml("a" + "<sup>" + "2" + "</sup>" + " + "
                + "b" + "<sup>" + "2" + "</sup>" + "=" + "(" + "a-b" + ")"
                + "<sup>" + "2" + "</sup>" + " + " + "2ab"));

        water.setText(Html.fromHtml("H" + "<sub>" + "2" + "</sub>" + "O"));

    }

}

here sup mansion superscript and sub mansion subscript.

And activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    tools:context="com.example.textview.MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="TextView" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="TextView" />

</LinearLayout>

Best of luck!

回答5:

I would not try to bend the TextView widget to make that. Instead, you could easily make your own widget that has 2 different paints: one for the element name (big font size) and one for the numbers (small size, italics).

You'd make proper setters and store each property separatly instead of storing a big spannable or string.

You'd also be able to easily align both horizontally and vertically (numbers at top and bottom of element name)

To compute the width, you can have a property to adjust the padding between numbers and element name. Then you can use each paint to compute the text width and add all this (don't forget to add the widget padding values).

回答6:

you can also refer my answer in this link Simply use SpannableString that will solve your problem.

 SpannableString styledString = new SpannableString("9-10th STD");
 styledString.setSpan(new SuperscriptSpan(), 4, 6, 0);
 textView.setText(styledString);

and put your android:textAllCaps="false"

来源：https://stackoverflow.com/questions/23990381/how-to-create-vertically-aligned-superscript-and-subscript-in-textview

标签

android

textview

subscript

superscript