Android自定义view实现圆的扩散效果

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public class MainActivity extends AppCompatActivity {
  private Button button;
  private Button button2;
  private DiffuseView diffuseView;


  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    button =  findViewById(R.id.button);
    button2 =  findViewById(R.id.button2);
    diffuseView = findViewById(R.id.diffuseView);

    button.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        diffuseView.start();
      }
    });

    button2.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        diffuseView.stop();
      }
    });
  }
}

public class DiffuseView extends View {

  /** 扩散圆圈颜色 */
  private int mColor = getResources().getColor(R.color.colorAccent);
  /** 圆圈中心颜色 */
  private int mCoreColor = getResources().getColor(R.color.colorPrimary);
  /** 中心圆半径 */
  private float mCoreRadius = 150;
  /** 扩散圆宽度 */
  private int mDiffuseWidth = 3;
  /** 最大宽度 */
  private Integer mMaxWidth = 255;
  /** 扩散速度 */
  private int mDiffuseSpeed = 5;
  /** 是否正在扩散中 */
  private boolean mIsDiffuse = false;
  // 透明度集合
  private List mAlphas = new ArrayList<>();
  // 扩散圆半径集合
  private List mWidths = new ArrayList<>();
  private Paint mPaint;

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

  public DiffuseView(Context context, AttributeSet attrs) {
    this(context, attrs, -1);
  }

  public DiffuseView(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();

    TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.DiffuseView, defStyleAttr, 0);
    mColor = a.getColor(R.styleable.DiffuseView_diffuse_color, mColor);
    mCoreColor = a.getColor(R.styleable.DiffuseView_diffuse_coreColor, mCoreColor);
    mCoreRadius = a.getFloat(R.styleable.DiffuseView_diffuse_coreRadius, mCoreRadius);
    mDiffuseWidth = a.getInt(R.styleable.DiffuseView_diffuse_width, mDiffuseWidth);
    mMaxWidth = a.getInt(R.styleable.DiffuseView_diffuse_maxWidth, mMaxWidth);
    mDiffuseSpeed = a.getInt(R.styleable.DiffuseView_diffuse_speed, mDiffuseSpeed);
    a.recycle();
  }

  private void init() {
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mAlphas.add(255);
    mWidths.add(0);
  }

  @Override
  public void invalidate() {
    if(hasWindowFocus()){
      super.invalidate();
    }
  }

  @Override
  public void onWindowFocusChanged(boolean hasWindowFocus) {
    super.onWindowFocusChanged(hasWindowFocus);
    if(hasWindowFocus){
      invalidate();
    }
  }

  @Override
  public void onDraw(Canvas canvas) {
    // 绘制扩散圆
    mPaint.setColor(mColor);
    for (int i = 0; i < mAlphas.size(); i ++) {
      // 设置透明度
      Integer alpha = mAlphas.get(i);
      mPaint.setAlpha(alpha);
      // 绘制扩散圆
      Integer width = mWidths.get(i);
      canvas.drawCircle(getWidth() / 2, getHeight() / 2, mCoreRadius + width, mPaint);

      if(alpha > 0 && width < mMaxWidth){
        mAlphas.set(i, alpha - mDiffuseSpeed > 0 ? alpha - mDiffuseSpeed : 1);
        mWidths.set(i, width + mDiffuseSpeed);
      }
    }
    // 判断当扩散圆扩散到指定宽度时添加新扩散圆
    if (mWidths.get(mWidths.size() - 1) >= mMaxWidth / mDiffuseWidth) {
      mAlphas.add(255);
      mWidths.add(0);
    }
    // 超过10个扩散圆，删除最外层
    if(mWidths.size() >= 10){
      mWidths.remove(0);
      mAlphas.remove(0);
    }

    // 绘制中心圆
    mPaint.setAlpha(255);
    mPaint.setColor(mCoreColor);
    canvas.drawCircle(getWidth() / 2, getHeight() / 2, mCoreRadius, mPaint);

    if(mIsDiffuse){
      invalidate();
    }
  }

  /**
   * 开始扩散
   */
  public void start() {
    mIsDiffuse = true;
    invalidate();
  }

  /**
   * 停止扩散
   */
  public void stop() {
    mIsDiffuse = false;
    mWidths.clear();
    mAlphas.clear();
    mAlphas.add(255);
    mWidths.add(0);
    invalidate();
  }

  /**
   * 是否扩散中
   */
  public boolean isDiffuse(){
    return mIsDiffuse;
  }

  /**
   * 设置扩散圆颜色
   */
  public void setColor(int colorId){
    mColor = colorId;
  }

  /**
   * 设置中心圆颜色
   */
  public void setCoreColor(int colorId){
    mCoreColor = colorId;
  }

  /**
   * 设置中心圆半径
   */
  public void setCoreRadius(int radius){
    mCoreRadius = radius;
  }

  /**
   * 设置扩散圆宽度(值越小宽度越大)
   */
  public void setDiffuseWidth(int width){
    mDiffuseWidth = width;
  }

  /**
   * 设置最大宽度
   */
  public void setMaxWidth(int maxWidth){
    mMaxWidth = maxWidth;
  }

  /**
   * 设置扩散速度，值越大速度越快
   */
  public void setDiffuseSpeed(int speed){
    mDiffuseSpeed = speed;
  }
}

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