Android自定義View實現(xiàn)飄動的葉子效果（三）

更新時間：2017年03月23日 10:25:23 作者：罔少年

這篇文章主要為大家詳細介紹了Android自定義View實現(xiàn)飄動的葉子效果，具有一定的參考價值，感興趣的小伙伴們可以參考一下

上一篇對自定義View及一些方法有所了解，下面做一個簡單的葉子飄動的例子

主要技術(shù)點

1、添加背景圖片canvas.drawBitmap()

2、Matrix動畫類

3、Matrix添加到畫布上

步驟

1、添加背景顏色

public LeafView(Context context, AttributeSet attrs) {
  super(context, attrs);
  bgPaint = new Paint();
  bgPaint.setColor(mResources.getColor(R.color.bg_color));
 }


 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  width = w;
  height = h;
 }

 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  bgRect = new RectF(0, 0 , width, height);
  canvas.drawRect(bgRect, bgPaint);
}

2、添加背景圖片

 public LeafView(Context context, AttributeSet attrs) {
  super(context, attrs);
  mResources = getResources();
  bgBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf_kuang, null)).getBitmap();
  bgPaint = new Paint();
  bgPaint.setColor(mResources.getColor(R.color.bg_color));
 }


 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  width = w;
  height = h;
  bgDestRect = new Rect(0, 0 , width, height);
 }

 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  bgRect = new RectF(0, 0 , width, height);
  canvas.drawRect(bgRect, bgPaint);
  canvas.drawBitmap(bgBitmap, null, bgDestRect, null);
}

canvas.drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint) 添加圖片到畫布

Rect src：圖片剪裁,null圖片顯示全屏， RectF dst：圖片在Canvas畫布區(qū)域

3、添加葉子

public LeafView(Context context, AttributeSet attrs) {
  super(context, attrs);
  mResources = getResources();
  bgBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf_kuang, null)).getBitmap();
  leafBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf, null))).getBitmap();
  bgPaint = new Paint();
  bgPaint.setColor(mResources.getColor(R.color.bg_color));
 }


 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  width = w;
  height = h;
  bgDestRect = new Rect(0, 0 , width, height);
 }

 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  bgRect = new RectF(0, 0 , width, height);
  //添加背景
  canvas.drawRect(bgRect, bgPaint);
  //添加背景圖片
  canvas.drawBitmap(bgBitmap, null, bgDestRect, null);
  //添加葉子
  canvas.drawBitmap(leafBitmap, new Matrix(), new Paint());
}

canvas.drawBitmap(Bitmap bitmap, Matrix matrix, Paint paint)添加一個帶動畫的bitmap到畫布

這里matrix什么都沒定義，所以默認如下顯示，左上角葉子

4、給葉子添加Matrix動畫

Matrix作用：

a、translate 平移

b、rotate 旋轉(zhuǎn)

c、scale 縮放

d、skew 傾斜

這里要用到matrix.postTranslate(float x, float y)，以畫布左上角為(0,0); xy為平移絕對值

public LeafView(Context context, AttributeSet attrs) {
  super(context, attrs);
  mResources = getResources();
  bgBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf_kuang, null)).getBitmap();
  leafBitmap = ((BitmapDrawable) mResources.getDrawable(R.drawable.leaf, null))).getBitmap();
  mLeafHeight = leafBitmap.getWidht();  

  bgPaint = new Paint();
  bgPaint.setColor(mResources.getColor(R.color.bg_color));
 }

 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  width = w;
  height = h;
  bgDestRect = new Rect(0, 0 , width, height);
 }

 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  bgRect = new RectF(0, 0 , width, height);
  //添加背景
  canvas.drawRect(bgRect, bgPaint);
  //添加背景圖片
  canvas.drawBitmap(bgBitmap, null, bgDestRect, null);
  //添加葉子
  Matrix matrix = new Matrix();
  matrix.postTranslate(getMatriX(), (height-mLeadHeight)/2);
  canvas.drawBitmap(leafBitmap, new Matrix(), new Paint());
  //重復調(diào)用onDraw()
  postInvalidate();
 }
 long cycleTime = 5000; //葉子滑動一周的時間5秒
 long startTime = 0;  //葉子滑動開始時間
 private float getMatriX() {
  float betweenTime = startTime - System.currentTimeMillis();
  //周期結(jié)束再加一個cycleTime
  if(betweenTime < 0) {
   startTime = System.currentTimeMillis() + cycleTime;
   betweenTime = cycleTime;
  }
  //通過時間差計算出葉子的坐標
  float fraction = (float) betweenTime / cycleTime;
  float x = (int)(width * fraction);
  return x;
 }

好了，看到的效果就是如下，由于Matrix沒有設置動畫時間長度概念，所以通過時間差來計算出位移值的方式，來設置滑動快慢