自定义textview在不同的android api级别上的不同行为

Question

我在android中遇到自定义文本视图组件的问题。我使用自定义spannable来设置textview的背景，如第一张图片中所示。这适用于android api level 21（第一张图片）。但是如果我使用api level 25（第二张图片），自定义textview就会消失。

自定义文字视图中的代码

public class MetalTextView extends android.support.v7.widget.AppCompatTextView
{
private final String xmlns = "http://schemas.android.com/apk/res/android";

private Context context;

private AttributeSet attributeSet;

private String value;

public MetalTextView(Context context)
{
    super(context);
    this.context = context;

    value = attributeSet.getAttributeValue(xmlns, "text");
}

public MetalTextView(Context context, @Nullable AttributeSet attrs)
{
    super(context, attrs);
    this.context = context;
    this.attributeSet = attrs;

    value = attributeSet.getAttributeValue(xmlns, "text");
}

public MetalTextView(Context context, AttributeSet attrs, int defStyleAttr)
{
    super(context, attrs, defStyleAttr);
    this.context = context;
    this.attributeSet = attrs;

    value = attributeSet.getAttributeValue(xmlns, "text");
}

@Override
protected void onDraw(Canvas canvas)
{
    super.onDraw(canvas);
    final Spannable spannable = new SpannableString(value);
    spannable.setSpan(new RoundedBackgroundSpannable(), 0, value.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
    this.setText(spannable);
}

@Override
public void setText(CharSequence text, BufferType type)
{
    super.setText(text, type);
    value = text.toString();
    final Spannable spannable = new SpannableString(text);
    spannable.setSpan(new RoundedBackgroundSpannable(), 0, value.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
}
}

来自我的客户的代码spannable

public class RoundedBackgroundSpannable extends ReplacementSpan
{
private static int CORNER_RADIUS = 20;

private final int backgroundColor = 0xFFFFFFFF;
private final int textColor = 0xFF000000;
private final int borderColor = 0xFF000000;

private final float strokeWidth = 5f;

public RoundedBackgroundSpannable()
{
    super();
}

@Override
public void draw(Canvas canvas, CharSequence text, int start, int end, float x, int top, int y, int bottom, Paint paint)
{

    final RectF rectF = new RectF(x, top, x + measureText(paint, text, start, end ), bottom);
    paint.setColor(backgroundColor);
    canvas.drawRoundRect(rectF, CORNER_RADIUS, CORNER_RADIUS, paint);

    paint.setColor(textColor);
    canvas.drawText(text, start, end, x, y, paint);

    paint.setColor(borderColor);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(strokeWidth);

    final Path path = new Path();
    path.addRoundRect(rectF, CORNER_RADIUS, CORNER_RADIUS, Path.Direction.CW);
    canvas.drawPath(path, paint);
}

@Override
public int getSize(Paint paint, CharSequence text, int start, int end, Paint.FontMetricsInt fm)
{
    return Math.round(paint.measureText(text, start, end));
}

private float measureText(Paint paint, CharSequence text, int start, int end)
{
    return paint.measureText(text, start, end);
}
}

我对自定义组件的使用

<com.metalcrunch.ui.MetalTextView
    android:id="@+id/metalTextView"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_marginTop="@dimen/textview_headline_margin_top"
    android:layout_weight="0.1"
    android:gravity="center"
    android:text="Some Text"
    android:textSize="@dimen/textview_headline_text_size"/>

textview在api 25级消失的原因是什么？