android开发 textview根据字数长度自动调整字体大小

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);
////        }
//    }

}

使用：（注意不能给默认字体大小，否则有问题）

<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的TextView控件会在文字上下加上默认的padding值，该值随着文字大小成正比变化，只要为TextView设置android:includeFontPadding=”false”;就可以减少大部分上下空白，而且如果文字sp值小，也就看不出空白了