Android实现未读消息小红点显示实例

import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.ShapeDrawable;

import androidx.annotation.IntRange;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;


public class CircleDrawable extends ShapeDrawable {
    private Paint mPaint;
    private int mRadio;

    public CircleDrawable(int radio, int painColor) {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setColor(painColor);
        mRadio = radio;
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        canvas.drawCircle(mRadio, mRadio, mRadio, mPaint);
    }

    @Override
    public void setAlpha(@IntRange(from = 0, to = 255) int i) {
        mPaint.setAlpha(i);
    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {
        mPaint.setColorFilter(colorFilter);
    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }

    /***
     * drawable实际宽高，圆形关键
     *
     * @return
     */
    @Override
    public int getIntrinsicWidth() {
        return mRadio * 2;
    }

    @Override
    public int getIntrinsicHeight() {
        return mRadio * 2;
    }
}

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Rect;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.graphics.drawable.shapes.RoundRectShape;
import android.util.AttributeSet;
import android.util.Printer;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import android.widget.TextView;

import androidx.annotation.Nullable;

import com.primer.common.constant.GravityDirection;
import com.primer.common.mvp.LoginInterface;
import com.primer.common.util.LogHelper;
import com.primer.common.util.UiHelper;
import com.primer.common.view.drawable.CircleDrawable;

public class BadgeView extends TextView {

    private final int DEFAULT_BADGE_RADIO = 5;
    private final int DEFAULT_TEXT_SIZE = 5;
    private final int DEFAULT_TEXT_COLOR = Color.WHITE;
    private final int DEFAULT_BADGE_COLOR = Color.RED;
    private final int DEFAULT_BADGE_GRAVITY = GravityDirection.DIRECT_TOP_LEFT;

    private String mText;
    private int mBadgeColor = DEFAULT_BADGE_COLOR;
    private int mTextColor = DEFAULT_TEXT_COLOR;
    private int mTextSize = DEFAULT_TEXT_SIZE;
    private int mBadgeRadio = DEFAULT_BADGE_RADIO;
    private int mBadgeGravity = DEFAULT_BADGE_GRAVITY;

    private FrameLayout mFragmentLayout;
    private ViewGroup mTargetViewGroup;
    private View mTarget;
    private Context mContext;

    public BadgeView(Context context) {
        super(context);
        init(context);
    }

    public BadgeView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public BadgeView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    public BadgeView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init(context);
    }

    private void init(Context context) {
        mFragmentLayout = new FrameLayout(context);
        mFragmentLayout.setLayoutParams(new FrameLayout.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
        mContext = context;
    }

    /***
     *
     * @param content
     * @param target
     * @param textColor
     * @param textSize
     * @param badgeColor
     * @param badgeRadio
     */
    public void showBadgeView(String content, View target, int textColor, int textSize, int badgeColor, int badgeRadio) {
        if (target == null) {
            throw new IllegalArgumentException("target view must not be null");
        }

        mTarget = target;
        mTargetViewGroup = (ViewGroup) target.getParent();
        mTargetViewGroup.removeView(target);
        mTargetViewGroup.addView(mFragmentLayout, target.getLayoutParams());

        setTextColor(mTextColor);
        setTextSize(mTextSize);
        setGravity(Gravity.CENTER);
        if (content != null && content.length() <= 3) {
            setText(content);
        }

          //文字和半径之间的适配
        if (content != null) {
            Rect rect = new Rect();
            this.getPaint().getTextBounds(content, 0, content.length(), rect);
            if (content.length() <= 3 && rect.width() >= mBadgeRadio) {
                mBadgeRadio = (UiHelper.px2dip(mContext, rect.width()) / 2) + 1;
            }
        }

        setBackgroundDrawable(getShapeDrawable());
        mFragmentLayout.addView(target);
        mFragmentLayout.addView(this);
        mTargetViewGroup.invalidate();
    }


    private ShapeDrawable getShapeDrawable() {
        int radio = UiHelper.dip2px(mContext, mBadgeRadio);
        CircleDrawable drawable = new CircleDrawable(radio, mBadgeColor);
        return drawable;
    }

    /***
     *
     * @param content
     * @param target
     */
    public void showBadgeView(String content, View target) {
        showBadgeView(content, target,
                DEFAULT_TEXT_COLOR,
                DEFAULT_TEXT_SIZE,
                DEFAULT_BADGE_COLOR,
                DEFAULT_BADGE_RADIO);
    }

    public void showBadgeView(View target) {
        showBadgeView(null, target,
                DEFAULT_TEXT_COLOR,
                DEFAULT_TEXT_SIZE,
                DEFAULT_BADGE_COLOR,
                DEFAULT_BADGE_RADIO);
    }

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

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

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

    private BadgeView mReadBadgeView;
    private TextView mRead;

	mReadBadgeView = new BadgeView(getActivity());
    mReadBadgeView.showBadgeView("+99", mRead);