消息提醒---帶陰影的圓形小球

自定義的屬性

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="RedDotTextView">
        <attr name="shadowWidth" format="dimension" />
        <attr name="circleBackground" format="reference|color" />
    </declare-styleable>
</resources>

java代碼

public class RedDotTextView extends AppCompatTextView {

    private Paint mPaint;
    private RectF mBgRect;
    private int mShadowWidth;
    private int mBgColor;

    public RedDotTextView(Context context) {
        super(context);
        init(context, null);
    }

    public RedDotTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public RedDotTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context, attrs);
    }

    private void init(Context context, AttributeSet attrs){
        if (attrs != null) {
            TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.RedDotTextView, 0, 0);
            try {
                if (a.hasValue(R.styleable.RedDotTextView_shadowWidth)) {
                    mShadowWidth = a.getDimensionPixelSize(R.styleable.RedDotTextView_shadowWidth, -1);
                }
                if (a.hasValue(R.styleable.RedDotTextView_circleBackground)) {
                    mBgColor = a.getColor(R.styleable.RedDotTextView_circleBackground, 0);
                }
            } finally {
                a.recycle();
            }
        }

        mPaint = new Paint();
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setAntiAlias(true);
        mPaint.setColor(mBgColor);
        mPaint.setShadowLayer(1, 0, mShadowWidth, Color.parseColor("#7f565656"));
        setLayerType(LAYER_TYPE_SOFTWARE, mPaint);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        int width = getWidth();
        mBgRect = new RectF(0, 0, width, width);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawArc(mBgRect, 0, 360, false, mPaint);
        super.onDraw(canvas);
    }
}

使用：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.test.reddottextview.MainActivity">

    <com.test.reddottextview.RedDotTextView
        android:layout_width="50dp"
        android:layout_height="51dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:shadowWidth="1dp"
        app:circleBackground="@color/colorAccent"
        android:text="hello"
        android:gravity="center"/>

</android.support.constraint.ConstraintLayout>

效果：