需求：
需要动态更改TextView内容字体的大小，比如设定TextView只有一行，宽度只有200dp，内容超过这个之后就缩小字体显示，只能能将字体都显示完全；也就是动态更改TextView的字体大小，当TextView的内容比较多时缩小显示，当TextView的内容比较少时正常显示。
使用框架:Android-autofittextview
地址：/grantland/android-autofittextview
使用方式详见官网介绍。
例子展示:
可以看出来：当文字没有填充TextView完全时显示的就是默认的字体，当文字能够完全填充TextView并且一行显示不下时，他会默认的缩小文字的字体，当文字再多时，他会默认在末尾省略。
AutofitTextView.java代码：
package me.grantland.widget;import android.content.Context;import android.util.AttributeSet;import android.util.TypedValue;import android.widget.TextView;/*** A {@link TextView} that re-sizes its text to be no larger than the width of the view.** @attr ref R.styleable.AutofitTextView_sizeToFit* @attr ref R.styleable.AutofitTextView_minTextSize* @attr ref R.styleable.AutofitTextView_precision*/public class AutofitTextView extends TextView implements AutofitHelper.OnTextSizeChangeListener {private AutofitHelper mHelper;public AutofitTextView(Context context) {super(context);init(context, null, 0);}public AutofitTextView(Context context, AttributeSet attrs) {super(context, attrs);init(context, attrs, 0);}public AutofitTextView(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);init(context, attrs, defStyle);}private void init(Context context, AttributeSet attrs, int defStyle) {mHelper = AutofitHelper.create(this, attrs, defStyle).addOnTextSizeChangeListener(this);}// Getters and Setters/*** {@inheritDoc}*/@Overridepublic void setTextSize(int unit, float size) {super.setTextSize(unit, size);if (mHelper != null) {mHelper.setTextSize(unit, size);}}/*** {@inheritDoc}*/@Overridepublic void setLines(int lines) {super.setLines(lines);if (mHelper != null) {mHelper.setMaxLines(lines);}}/*** {@inheritDoc}*/@Overridepublic void setMaxLines(int maxLines) {super.setMaxLines(maxLines);if (mHelper != null) {mHelper.setMaxLines(maxLines);}}/*** Returns the {@link AutofitHelper} for this View.*/public AutofitHelper getAutofitHelper() {return mHelper;}/*** Returns whether or not the text will be automatically re-sized to fit its constraints.*/public boolean isSizeToFit() {return mHelper.isEnabled();}/*** Sets the property of this field (sizeToFit), to automatically resize the text to fit its* constraints.*/public void setSizeToFit() {setSizeToFit(true);}/*** If true, the text will automatically be re-sized to fit its constraints; if false, it will* act like a normal TextView.** @param sizeToFit*/public void setSizeToFit(boolean sizeToFit) {mHelper.setEnabled(sizeToFit);}/*** Returns the maximum size (in pixels) of the text in this View.*/public float getMaxTextSize() {return mHelper.getMaxTextSize();}/*** Set the maximum text size to the given value, interpreted as "scaled pixel" units. This size* is adjusted based on the current density and user font size preference.** @param size The scaled pixel size.** @attr ref android.R.styleable#TextView_textSize*/public void setMaxTextSize(float size) {mHelper.setMaxTextSize(size);}/*** Set the maximum text size to a given unit and value. See TypedValue for the possible* dimension units.** @param unit The desired dimension unit.* @param size The desired size in the given units.** @attr ref android.R.styleable#TextView_textSize*/public void setMaxTextSize(int unit, float size) {mHelper.setMaxTextSize(unit, size);}/*** Returns the minimum size (in pixels) of the text in this View.*/public float getMinTextSize() {return mHelper.getMinTextSize();}/*** Set the minimum text size to the given value, interpreted as "scaled pixel" units. This size* is adjusted based on the current density and user font size preference.** @param minSize The scaled pixel size.** @attr ref me.grantland.R.styleable#AutofitTextView_minTextSize*/public void setMinTextSize(int minSize) {mHelper.setMinTextSize(PLEX_UNIT_SP, minSize);}/*** Set the minimum text size to a given unit and value. See TypedValue for the possible* dimension units.** @param unit The desired dimension unit.* @param minSize The desired size in the given units.** @attr ref me.grantland.R.styleable#AutofitTextView_minTextSize*/public void setMinTextSize(int unit, float minSize) {mHelper.setMinTextSize(unit, minSize);}/*** Returns the amount of precision used to calculate the correct text size to fit within its* bounds.*/public float getPrecision() {return mHelper.getPrecision();}/*** Set the amount of precision used to calculate the correct text size to fit within its* bounds. Lower precision is more precise and takes more time.** @param precision The amount of precision.*/public void setPrecision(float precision) {mHelper.setPrecision(precision);}@Overridepublic void onTextSizeChange(float textSize, float oldTextSize) {// do nothing}}
原理：
AutofitTextView：自定义TextView并继承系统的TextView，然后在绘制组件的时候根据getMaxLines方法获取内容的行数若内容的行数大于1，则缩小文字的字体，然后在尝试获取getMaxLines方法，若内容的行数还是大于1，则缩小文字的字体，直到内容能够一行显示或者是字体缩小大一定的大小，这时候若缩小到一定的大小还是不能一行显示，则尾部省略。
延伸：
TextView源码中：
public void setTextSize(float size) {setTextSize(PLEX_UNIT_SP, size);}public void setTextSize(int unit, float size) {Context c = getContext();Resources r;if (c == null)r = Resources.getSystem();elser = c.getResources();setRawTextSize(TypedValue.applyDimension(unit, size, r.getDisplayMetrics()));}
setTextSize(int unit, int size)
第一个参数可设置如下静态变量：
PLEX_UNIT_PX : Pixels
PLEX_UNIT_SP : Scaled Pixels
PLEX_UNIT_DIP : Device Independent Pixels
我们在使用TextView控件时，调用setTextSize方法，默认就是以sp为单位，与xml配置文件默认保存一致。
参考：/qq_23547831/article/details/50592352
