概述

在專案中遇到需求就是，標題根據文字的長度自動適配字號大小和換行顯示，因為標題可能很長然後顯示不完全。

實現

根據需求，很容易想到根據TextView的寬高和文字長度計算字號，然後重新設定TextView字號。

/**
 * @author Wastrel
 * @date 建立時間：2016年8月19日 上午9:12:01
 * TODO
 */

import android.content.Context;
import android.text.Layout;
import android.text.StaticLayout;
import android.text.TextPaint;
import
 
 android.text.TextUtils;
import android.util.AttributeSet;
import android.util.Log;
import android.util.TypedValue;
public class AutoFitTextView extends android.support.v7.widget.AppCompatTextView {

    private static float DEFAULT_MIN_TEXT_SIZE = 15;
    private static float DEFAULT_MAX_TEXT_SIZE = 50
 
;

    private TextPaint testPaint;
    private float minTextSize;
    private float maxTextSize;

    public AutoFitTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initialise();
    }

    private void initialise() {
        testPaint = new TextPaint();
        testPaint.set(this
 
.getPaint());
        // max size defaults to the intially specified text size unless it is
        // too small
        maxTextSize = this.getTextSize();
        if (maxTextSize <= DEFAULT_MIN_TEXT_SIZE) {
            maxTextSize = DEFAULT_MAX_TEXT_SIZE;
        }
        minTextSize = DEFAULT_MIN_TEXT_SIZE;
    }

    /**
     * Re size the font so the specified text fits in the text box
     * assuming the text box is the specified width.
     */
    private void refitText(String text, int textWidth, int textHeight) {
        if (textWidth > 0 && textHeight > 0) {
            //allow diplay rect
            int availableWidth = textWidth - this.getPaddingLeft() - this.getPaddingRight();
            int availableHeight = textHeight - this.getPaddingBottom() - this.getPaddingTop();
            //by the line calculate allow displayWidth
            int autoWidth = availableWidth;
            float mult = getLineSpacingMultiplier();
            float add = getLineSpacingExtra();
            float trySize = maxTextSize;
            testPaint.setTextSize(trySize);
            int lineCount = 1;
            while ((trySize > minTextSize)) {
                StaticLayout layout = new StaticLayout(text, testPaint, autoWidth, Layout.Alignment.ALIGN_NORMAL, mult, add, true);
                int displayH = layout.getHeight();
                if (displayH < availableHeight) {
                    lineCount = layout.getLineCount();
                    break;
                }
                trySize--;
                if (trySize <= minTextSize) {
                    trySize = minTextSize;
                    break;
                }
                testPaint.setTextSize(trySize);
            }
            //setMultiLine
            if (lineCount > 1) {
                this.setSingleLine(false);
                this.setMaxLines(lineCount);
                this.setEllipsize(TextUtils.TruncateAt.END);
            }
            this.setTextSize(TypedValue.COMPLEX_UNIT_PX, trySize);
        }
    }

    @Override
    protected void onTextChanged(CharSequence text, int start, int before, int after) {
        super.onTextChanged(text, start, before, after);
        refitText(text.toString(), this.getWidth(), this.getHeight());
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        Log.e("TagSizeChange", "new(" + w + "," + h + ") old(" + oldw + "" + oldh + ")");
        if (w != oldw || h != oldh) {
            refitText(this.getText().toString(), w, h);
        }
    }
}

程式碼註釋很詳細，具體的請看程式碼。

效果

佈局檔案使用：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.autofittext.MainActivity">

    <com.example.autofittext.AutoFitTextView
        android:background="#80808080"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:textSize="30sp"
        android:gravity="center"
        android:text="@string/str10" />
    <com.example.autofittext.AutoFitTextView
        android:layout_marginTop="15dp"
        android:background="#80808080"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:gravity="center"
        android:textSize="30sp"
        android:text="@string/str20"/>


    <com.example.autofittext.AutoFitTextView
        android:layout_marginTop="15dp"
        android:background="#80808080"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:gravity="center"
        android:textSize="30sp"
        android:text="@string/str30"/>

    <com.example.autofittext.AutoFitTextView
        android:layout_marginTop="15dp"
        android:background="#80808080"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:textSize="30sp"
        android:gravity="center"
        android:text="@string/str40"/>
    <com.example.autofittext.AutoFitTextView
        android:layout_marginTop="15dp"
        android:background="#80808080"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:gravity="center"
        android:textSize="30sp"
        android:text="@string/str50"/>
    <com.example.autofittext.AutoFitTextView
        android:layout_marginTop="15dp"
        android:background="#80808080"
        android:gravity="center"
        android:textSize="30sp"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="@string/str60"/>
    <com.example.autofittext.AutoFitTextView
        android:layout_marginTop="15dp"
        android:background="#80808080"
        android:gravity="center"
        android:textSize="30sp"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="@string/str70"/>
</LinearLayout>

後記

• 使用的時候儘量對TextView的寬高限制。wrap_content 可能達不到想要的效果。
• 如果想多行的時候左對齊，那麼可以在設定多行的時候對Gravity 屬性進行設定。