上一篇对自定义View及一些方法有所了解，下面做一个简单的叶子飘动的例子
主要技术点
1、添加背景图片canvas.drawBitmap()
2、Matrix动画类
3、Matrix添加到画布上
步骤
1、添加黄色背景颜色
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、添加背景图片
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) 添加图片到画布
Rect src：图片剪裁,null图片显示全屏， RectF dst：图片在Canvas画布区域
3、添加叶子
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);
//添加黄色背景
canvas.drawRect(bgRect, bgPaint);
//添加背景图片
canvas.drawBitmap(bgBitmap, null, bgDestRect, null);
//添加叶子
canvas.drawBitmap(leafBitmap, new Matrix(), new Paint());
}
canvas.drawBitmap(Bitmap bitmap, Matrix matrix, Paint paint)添加一个带动画的bitmap到画布
这里matrix什么都没定义，所以默认如下显示，左上角叶子
4、给叶子添加Matrix动画
Matrix作用：
a、translate 平移
b、rotate 旋转
c、scale 缩放
d、skew 倾斜
这里要用到matrix.postTranslate(float x, float y)，以画布左上角为(0,0); xy为平移绝对值
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);
//添加黄色背景
canvas.drawRect(bgRect, bgPaint);
//添加背景图片
canvas.drawBitmap(bgBitmap, null, bgDestRect, null);
//添加叶子
Matrix matrix = new Matrix();
matrix.postTranslate(getMatriX(), (height-mLeadHeight)/2);
canvas.drawBitmap(leafBitmap, new Matrix(), new Paint());
//重复调用onDraw()
postInvalidate();
}
long cycleTime = 5000; //叶子滑动一周的时间5秒
long startTime = 0; //叶子滑动开始时间
private float getMatriX() {
float betweenTime = startTime - System.currentTimeMillis();
//周期结束再加一个cycleTime
if(betweenTime < 0) {
startTime = System.currentTimeMillis() + cycleTime;
betweenTime = cycleTime;
}
//通过时间差计算出叶子的坐标
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没有设置动画时间长度概念，所以通过时间差来计算出位移值的方式，来设置滑动快慢
完整代码不贴了，就把上面这段代码复制到一个LeafView extends View中，然后在里面定义几个全局变量就好了。
