TextView文字描边实现

需求描述

文字显示在图片的上面，图片的内容是不确定了，为了防止文字与图片的颜色相近导致用户看不到或者看不清文字的问题，所以显示文字描边，避免问题。

实现

实现思想

使用TextPaint绘制相同文字在TextView的底部，TextPaint的字显示要比原始的字大一些，这样看起来就像是有描边的文字。

代码

1.attrs.xml文件

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <!-- 有描边的自定义TextView-->
    <declare-styleable name="StrokeTextView">
        <!--描边的颜色 -->
        <attr name="stroke_color" format="color" />
        <!-- 描边的宽度 -->
        <attr name="stroke_width" format="dimension" />
    </declare-styleable>

</resources>

2.StrokeTextView的实现

package com.zm.autostroketextview;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.ViewGroup;
import android.widget.TextView;

/**
 * 文字内容有描边的TextView
 * Author: zhangmiao
 * Date: 2018/4/13
 */
public class StrokeTextView extends TextView {

    private TextView outlineTextView = null;

    public StrokeTextView(Context context) {
        this(context, null);
    }

    public StrokeTextView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public StrokeTextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        outlineTextView = new TextView(context, attrs, defStyleAttr);
        init(attrs);
    }

    private void init(AttributeSet attrs) {
        //1.获取参数
        TypedArray ta = getContext().obtainStyledAttributes(attrs, R.styleable.StrokeTextView);
        int stroke_color = ta.getColor(R.styleable.StrokeTextView_stroke_color, Color.WHITE);
        float stroke_width = ta.getDimension(R.styleable.StrokeTextView_stroke_width, 2);

        //2.初始化TextPaint
        TextPaint paint = outlineTextView.getPaint();
        paint.setStrokeWidth(stroke_width);
        paint.setStyle(Paint.Style.STROKE);
        outlineTextView.setTextColor(stroke_color);
        outlineTextView.setGravity(getGravity());
    }

    @Override
    public void setLayoutParams(ViewGroup.LayoutParams params) {
        super.setLayoutParams(params);
        outlineTextView.setLayoutParams(params);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //设置轮廓文字
        CharSequence outlineText = outlineTextView.getText();

        if (outlineText == null || !outlineText.equals(getText())) {
            outlineTextView.setText(getText());
            postInvalidate();
        }
        outlineTextView.measure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        outlineTextView.layout(left, top, right, bottom);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        outlineTextView.draw(canvas);
        super.onDraw(canvas);
    }
}

3.布局文件中StrokeTextView的使用

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimary">

    <com.zm.autostroketextview.StrokeTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:stroke_color="@android:color/white"
        app:stroke_width="2dp" />

</LinearLayout>

4.结果显示