<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    **<item name="colorAccent">@color/colorPrimaryDark</item>**

//此時必須要設置其背景為空
<EditText
    android:background="@null"
    android:drawableBottom="@drawable/line"
    android:hint="請輸入您的手機號碼"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

//資源名稱為 drawable/line
<shape xmlns:android="http://schemas.android.com/apk/res/android">
  <solid android:color="@color/colorBlue" />
  <size
    android:height="1dp"
    android:width="1000dp" />
</shape>

public class UnderLineEditText extends EditText {
  private Paint paint;

  public UnderLineEditText(Context context, AttributeSet attrs) {
    super(context, attrs);
    //設置畫筆的屬性
    paint = new Paint();
    paint.setStyle(Paint.Style.STROKE);
    //設置畫筆顏色為紅色
    paint.setColor(Color.RED);
  }

  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    /**canvas畫直線，從左下角到右下角，this.getHeight()-2是獲得父edittext的高度，但是必須要-2這樣才能保證
     * 畫的橫線在edittext上面，和原來的下劃線的重合
     */
    canvas.drawLine(0, this.getHeight()-2, this.getWidth()-2, this.getHeight()-2, paint);
  }
}