Android 自定义设置文本字体间间距

自定义spacingtextview 继承textview，代码如下:

public class spacingtextview extends textview {
private float letterspacing = letterspacing.biggest;
private charsequence originaltext = “”;

public spacingtextview(context context) {
    super(context);
}

public spacingtextview(context context, attributeset attrs){
    super(context, attrs);
    originaltext = super.gettext();
    applyletterspacing();
    this.invalidate();
}

public spacingtextview(context context, attributeset attrs, int defstyle){
    super(context, attrs, defstyle);
}

public float getletterspacing() {
    return letterspacing;
}

public void setletterspacing(float letterspacing) {
    this.letterspacing = letterspacing;
    applyletterspacing();
}

@override
public void settext(charsequence text, buffertype type) {
    originaltext = text;
    applyletterspacing();
}

@override
public charsequence gettext() {
    return originaltext;
}

/**
 * 字距为任何字符串（技术上，一个简单的方法为charsequence不使用）的textview
 */
private void applyletterspacing() {
    if (this == null || this.originaltext == null) return;
    stringbuilder builder = new stringbuilder();
    for(int i = 0; i < originaltext.length(); i++) {
        string c = ""+ originaltext.charat(i);
        builder.append(c.tolowercase());
        if(i+1 < originaltext.length()) {
            builder.append("\u00a0");
        }
    }
    spannablestring finaltext = new spannablestring(builder.tostring());
    if(builder.tostring().length() > 1) {
        for(int i = 1; i < builder.tostring().length(); i+=2) {
            finaltext.setspan(new scalexspan((letterspacing+1)/10), i, i+1, spannable.span_exclusive_exclusive);
        }
    }
    super.settext(finaltext, buffertype.spannable);
}

public class letterspacing {
    public final static float normal = 0;
    public final static float normalbig = (float)0.025;
    public final static float big = (float)0.05;
    public final static float biggest = (float)0.2;
}

}

代码中调用：
public class spacingtextviewactivity extends baseactivity {

private spacingtextview spacingtextview;

@override
protected void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.activity_spacing_text_view);
    spacingtextview=findview(r.id.space_text);
    spacingtextview.settext(getresources().getstring(r.string.space_test));
    spacingtextview.setletterspacing(convertutils.dip2px(this,20));

}

}