上一篇對(duì)自定義View及一些方法有所了解，下面做一個(gè)簡(jiǎn)單的葉子飄動(dòng)的例子

主要技術(shù)點(diǎn)

1、添加背景圖片canvas.drawBitmap()

2、Matrix動(dòng)畫(huà)類

3、Matrix添加到畫(huà)布上

步驟

1、添加黃色背景顏色

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(huà)布

Rect src：圖片剪裁,null圖片顯示全屏，? RectF dst：圖片在Canvas畫(huà)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);

//添加黃色背景

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(gè)帶動(dòng)畫(huà)的bitmap到畫(huà)布

這里matrix什么都沒(méi)定義，所以默認(rèn)如下顯示，左上角葉子

4、給葉子添加Matrix動(dòng)畫(huà)

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(huà)布左上角為(0,0); xy為平移絕對(duì)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);

//添加黃色背景

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(fù)調(diào)用onDraw()

postInvalidate();

}

long cycleTime = 5000; //葉子滑動(dòng)一周的時(shí)間5秒

long startTime = 0; //葉子滑動(dòng)開(kāi)始時(shí)間

private float getMatriX() {

float betweenTime = startTime - System.currentTimeMillis();

//周期結(jié)束再加一個(gè)cycleTime

if(betweenTime < 0) {

startTime = System.currentTimeMillis() + cycleTime;

betweenTime = cycleTime;

}

//通過(guò)時(shí)間差計(jì)算出葉子的坐標(biāo)

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(méi)有設(shè)置動(dòng)畫(huà)時(shí)間長(zhǎng)度概念，所以通過(guò)時(shí)間差來(lái)計(jì)算出位移值的方式，來(lái)設(shè)置滑動(dòng)快慢

完整代碼不貼了，就把上面這段代碼復(fù)制到一個(gè)LeafView extends View中，然后在里面定義幾個(gè)全局變量就好了。

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