Android-解决TextView上下留白问题

缺乏、安全感 2022-07-16 09:50 714阅读 0赞

**问题**

1.  为什么TextView默认上下留空？  
    
2.  设置includeFontPadding参数，是否有效去除上下留空？

**includeFontPadding参数比较图**

![Center][]

**源码分析（展示重点方法）**

先看TextView计算过程：

protected void onMeasure( int widthMeasureSpec, int heightMeasureSpec) \{  
int heightMode = MeasureSpec .getMode(heightMeasureSpec);  
int heightSize = MeasureSpec .getSize(heightMeasureSpec);  
  
int height;  
  
*//计算宽度代码省略*  
  
if (heightMode == MeasureSpec .EXACTLY) \{  
*//准确设置高度*  
\} else \{  
*//自己计算高度*  
  
*//获取需要的高度*  
int desired = getDesiredHeight();  
  
height = desired;  
mDesiredHeightAtMeasure = desired;  
  
if (heightMode == MeasureSpec .AT\_MOST) \{  
height = Math .min(desired, heightSize);  
\}  
\}  
  
setMeasuredDimension(width, height);  
\}

TextView高度在getDesiredHeight( )中计算，而此方法简介调用getDesiredHeight( )方法

private int getDesiredHeight( Layout layout, boolean cap) \{  
  
int linecount = layout .getLineCount();  
int pad = getCompoundPaddingTop() \+ getCompoundPaddingBottom();  
int desired = layout .getLineTop(linecount);  
  
desired \+= pad;  
  
*//其他配置内容省略…*  
  
return desired;  
\}

desired值在BoringLayout.getLineTop( )中计算

public int getLineTop( int line) \{  
if (line == 0)  
return 0;  
else  
return mBottom;  
\}

mBottom值在BoringLayout.init( )中设置代码如下：

void init( CharSequence source,  
TextPaint paint, int outerwidth,  
Alignment align,  
float spacingmult, float spacingadd,  
BoringLayout . Metrics metrics, boolean includepad,  
boolean trustWidth) \{  
*//根据includepad参数，判断mBottom值*  
int spacing;  
if (includepad) \{  
spacing = metrics .bottom \- metrics .top;  
\} else \{  
spacing = metrics .descent \- metrics .ascent;  
\}  
mBottom = spacing;  
  
*//根据includepad参数，计算mDesc值*  
if (includepad) \{  
mDesc = spacing \+ metrics .top;  
\} else \{  
mDesc = spacing \+ metrics .ascent;  
\}  
  
*//根据includepad参数，设置TextView是否上下留白*  
if (includepad) \{  
mTopPadding = metrics .top \- metrics .ascent;  
mBottomPadding = metrics .bottom \- metrics .descent;

FontMetricsInt文字基准线介绍

public static class FontMetricsInt \{  
*/\*\*  
\* The maximum distance above the baseline for the tallest glyph in  
\* the font at a given text size.  
\*/*  
public int top;  
*/\*\*  
\* The recommended distance above the baseline for singled spaced text.  
\*/*  
public int ascent;  
*/\*\*  
\* The recommended distance below the baseline for singled spaced text.  
\*/*  
public int descent;  
*/\*\*  
\* The maximum distance below the baseline for the lowest glyph in  
\* the font at a given text size.  
\*/*  
public int bottom;  
*/\*\*  
\* The recommended additional space to add between lines of text.  
\*/*

public int leading;

![Center 1][]

详细介绍：[http://www.cnblogs.com/tianzhijiexian/p/4297664.html][http_www.cnblogs.com_tianzhijiexian_p_4297664.html]

**结论**

通过设置includeFontPadding参数，完全可以解决 TextView上下留白的问题。至于为什么中文情况下，没有说定到TextView的最上面，完全是因为中文没有到达基准线而已。

通过对“ap卡了ξτβㄎㄊěǔぬも┰┠”字段的展示，完全证明了我们的说法。

效果图如下：

![Center 2][]

[Center]: /images/20220716/6f3a82a06c284ded922d60b2f63c2aa5.png
[Center 1]: /images/20220716/d17e41fa72ab42c3b146c5a3aefb45e4.png
[http_www.cnblogs.com_tianzhijiexian_p_4297664.html]: http://www.cnblogs.com/tianzhijiexian/p/4297664.html
[Center 2]: /images/20220716/337deca4857f48c99b7e1a905454bcfc.png