android development textview automatically adjust the font size according to the length of words

import com.carspeak.client.util.DensityUtils;

import android.content.Context;
import android.graphics.Paint;
import android.graphics.Paint.FontMetrics;
import android.util.AttributeSet;
import android.util.Log;
import android.view.ViewGroup.LayoutParams;
import android.widget.TextView;

public class ShadowTextView extends TextView {
    private static float DEFAULT_MIN_TEXT_SIZE = 10;
    private static float DEFAULT_MAX_TEXT_SIZE = 85;

    // Attributes
    private Paint testPaint;
    private float minTextSize, maxTextSize;

    private String TAG = "ShadowTextView";
    public ShadowTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initialise();
    }

    public ShadowTextView(Context context) {
        super(context);
    }

    public ShadowTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onTextChanged(CharSequence text, int start,int lengthBefore, int lengthAfter) {
        super.onTextChanged(text, start, lengthBefore, lengthAfter);
        refitText(text.toString(), this.getWidth(),this.getHeight());
    }
    private void initialise() {
        testPaint = new Paint();
        testPaint.set(this.getPaint());
        // max size defaults to the intially specified text size unless it is
        // too small
        maxTextSize = this.getTextSize();
        if (maxTextSize <= DEFAULT_MAX_TEXT_SIZE) {
            maxTextSize = DEFAULT_MAX_TEXT_SIZE;
        }
        minTextSize = DEFAULT_MIN_TEXT_SIZE;
    };

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        if (w != oldw) {
//            refitText(this.getText().toString(), w);  //原本是需要执行的
        }
    }

    /**
     * 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) {
        
        int Length = text.length();
        //直接根据字符长度来调整字体大小  最大长度为20
//        this.setTextSize(DensityUtils.dp2px(this.getContext(), trySize));
//        testPaint.set(this.getPaint());
        if (textWidth > 0) {
            int availableWidth = textWidth - this.getPaddingLeft() - this.getPaddingRight();  //获取改TextView的画布可用大小        
            float trySize = maxTextSize;
            float scaled = getContext().getResources().getDisplayMetrics().scaledDensity;
//            Log.v(TAG, "availableWidth="+availableWidth + ";scaled="+scaled);
            testPaint.setTextSize(trySize*scaled);   //模拟 注意乘以scaled
            while ((trySize > minTextSize)&& (testPaint.measureText(text) > availableWidth)) 
            {
                
                trySize -= 2;
                FontMetrics fm = testPaint.getFontMetrics();
                double rowFontHeight = (Math.ceil(fm.descent - fm.top) + 2);
                float scaled1 = (float) (this.getHeight() /rowFontHeight );  //字体的行数   textview的总高度/每行字的高度
                float scaled2 = (float) ((testPaint.measureText(text) / availableWidth));  //也是行数  所有字的总长度/textview的有效宽度
                
//                Log.v(TAG, "trySize="+trySize + ";testPaint.measureText(text)="+testPaint.measureText(text)+";scaled1="+scaled1+";scaled2="+scaled2+";rowFontHeight="+rowFontHeight);
                if((scaled2*rowFontHeight*1.9)<this.getHeight())  //1.9代表是1.9的行高（1个字体本身，0.9的行距 ，大致差不多，没有实际测过）
                    break;
                if (trySize <= minTextSize) {
                    trySize = minTextSize;
                    break;
                }
                testPaint.setTextSize(trySize*scaled);
            }
            this.setTextSize(trySize);
//            Log.v(TAG, "trySize="+trySize+";maxTextSize="+maxTextSize+";minTextSize="+minTextSize);
        }
}
//    private void refitText(String text, int textWidth,int textHeight) {
////        if (textWidth > 0) {
////            int availableWidth = textWidth - this.getPaddingLeft() - this.getPaddingRight();  //获取改TextView的画布可用大小        
////            float trySize = maxTextSize;
////            float scaled = getContext().getResources().getDisplayMetrics().scaledDensity;
////            testPaint.setTextSize(trySize*scaled);   //模拟 注意乘以scaled
////            while ((trySize > minTextSize)&& (testPaint.measureText(text) > availableWidth)) {
////                trySize -= 2;
////                FontMetrics fm = testPaint.getFontMetrics();
////                float scaled1 = (float) (this.getHeight() / (Math.ceil(fm.descent - fm.top) + 2));
////                float scaled2 = (float) ((testPaint.measureText(text) / availableWidth));
////                if (scaled1 >= 1.75 & scaled1 >= scaled2) { // 注意1.75是三星s4 小米3  的适合数值（当然包括我的联想了)
////                    break;
////                }
////            if (trySize <= minTextSize) {
////                trySize = minTextSize;
////                break;
////            }
////            testPaint.setTextSize(trySize*scaled);
////            }
////            this.setTextSize(trySize);      //等同于this.getPaint().set(trySize*scaled);
////        }
//    }

}

:( careful not to use the default font size, or there is a problem)

<com.view.ShadowTextView
                    android:id="@+id/tv_shadow_preview"
                    android:layout_width="@dimen/projection_screen_width_4_3"
                    android:layout_height="@dimen/projection_screen_height_4_3"
                    android:layout_centerHorizontal="true"
                    android:background="#000"
                    android:text="字幕"
                    android:gravity="center"
                    android:textColor="#fff" />

Android TextView control will add the default value in the text padding up and down, the value changes as proportional to the size of text, as long as the set TextView android: includeFontPadding = "false"; you can reduce most of the blank up and down, but if the text value sp small, will not see a blank