Android TextView兩端對齊

Android TextView兩端對齊

Android中的TextView控件默認是做不到兩端對齊的，都是左對齊。可能的原因是安卓默認數字、字母不能為第一行以後每行的開頭字符，因為數字、字母為半角字符，還有就是文字中的英文字符占用1個字節，而一個漢字占用兩個字節。下面我就介紹下實現兩端對齊的原理：
1、測量一個中文漢字所占用的寬度
2、根據TextView的寬度和一個漢字所占用的寬度以及字符之間的間隔計算出總行數。
3、根據padding和margin以及行高計算出TextView的總高度。
4、繪制每一行的每一個字符
效果如下：

具體代碼如下：

package com.wedroid.framework.module.ui;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.text.TextPaint;
import android.text.TextUtils;
import android.util.AttributeSet;
import android.view.ViewGroup.MarginLayoutParams;
import android.view.ViewTreeObserver.OnPreDrawListener;
import android.widget.TextView;

public class WeDroidAlignTextView extends TextView {

    private boolean first = true;

    public WeDroidAlignTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
            @Override
            public boolean onPreDraw() {
                initTextInfo();
                return true;
            }
        });
    }

    public WeDroidAlignTextView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public WeDroidAlignTextView(Context context) {
        this(context, null, 0);
    }

    private float textSize;
    private float textLineHeight;
    private int top;
    private int y;
    private int lines;
    private int bottom;
    private int right;
    private int left;
    private int lineDrawWords;
    private char[] textCharArray;
    private float singleWordWidth;

    private float lineSpacingExtra;

    public void initTextInfo() {
        textSize = getTextSize();
        textLineHeight = getLineHeight();
        left = 0;
        right = getRight();
        y = getTop();
        // 要畫的寬度
        int drawTotalWidth = right - left;
        String text = getText().toString();
        if (!TextUtils.isEmpty(text) && first) {
            textCharArray = text.toCharArray();
            TextPaint mTextPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
            mTextPaint.density = getResources().getDisplayMetrics().density;
            mTextPaint.setTextSize(textSize);
            // 一個單詞的的寬度
            singleWordWidth = mTextPaint.measureText("一") + lineSpacingExtra;
            // 一行可以放多少個字符
            lineDrawWords = (int) (drawTotalWidth / singleWordWidth);
            int length = textCharArray.length;
            lines = length / lineDrawWords;
            if ((length % lineDrawWords) > 0) {
                lines = lines + 1;
            }
            first = false;
            MarginLayoutParams layoutParams = (MarginLayoutParams) getLayoutParams();
            int totalHeight = (int) (lines*textLineHeight+textLineHeight*2 + getPaddingBottom()+getPaddingTop()+layoutParams.bottomMargin+layoutParams.topMargin);
            setHeight(totalHeight);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        bottom = getBottom();
        int drawTotalLine = lines;

        if(maxLine!=0&&drawTotalLine>maxLine){
            drawTotalLine = maxLine;
        }

        for (int i = 0; i < drawTotalLine; i++) {
            try {
                int length = textCharArray.length;
                int mLeft = left;
                // 第i+1行開始的字符index
                int startIndex = (i * 1) * lineDrawWords;
                // 第i+1行結束的字符index
                int endTextIndex = startIndex + lineDrawWords;
                if (endTextIndex > length) {
                    endTextIndex = length;
                    y += textLineHeight;
                } else {
                    y += textLineHeight;
                }
                for (; startIndex < endTextIndex; startIndex++) {
                    char c = textCharArray[startIndex];
//                  if (c == ' ') {
//                      c = '\u3000';
//                  } else if (c < '\177') {
//                      c = (char) (c + 65248);
//                  }
                    canvas.drawText(String.valueOf(c), mLeft, y, getPaint());
                    mLeft += singleWordWidth;
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    int maxLine;

    public void setMaxLines(int max){
        this.maxLine = max;
    }

    public void setLineSpacingExtra(int lineSpacingExtra){
        this.lineSpacingExtra = lineSpacingExtra;
    }

     /** 
     * 判斷是否為中文 
     * @return 
     */  
    public static boolean containChinese(String string){  
        boolean flag = false;  
        for (int i = 0; i < string.length(); i++) {  
            char c = string.charAt(i);  
            if ((c >= 0x4e00) && (c <= 0x9FA5)) {  
                flag = true;  
            }  
        }  
        return flag;  
    }


    public static String ToDBC(String input) {
        // 導致TextView異常換行的原因：安卓默認數字、字母不能為第一行以後每行的開頭字符，因為數字、字母為半角字符
        // 所以我們只需要將半角字符轉換為全角字符即可
        char c[] = input.toCharArray();
        for (int i = 0; i < c.length; i++) {
            if (c[i] == ' ') {
                c[i] = '\u3000';
            } else if (c[i] < '\177') {
                c[i] = (char) (c[i] + 65248);
            }
        }
        return new String(c);
    }

}