Android小知识

Android一些琐碎小知识的积累记录,不定期更~

mDrawable.draw(canvas)使用;

Drawable mDrawable = getResources().getDrawable(R.drawable.music);
//获取drawable图像的真实宽高
int dHeight = mDrawable.getIntrinsicHeight();
int dWidth = mDrawable.getintrinsicWidth();
//在调用mDrawable.draw()方法前,必须要对mDrawable进行setBounds()
mDrawable.setBounds(0, 0, dWidth, dHeight);
//将mDrawable的图像信息画到画布上
mDrawable.draw(canvas);

ldpi	mdpi	hdpi	xhdpi	xxhdpi
120	160	240	320	480

Camera和Matrix简单使用

init();

Camera mCamera = new Camera();
Matrix mMatrix = new Matrix();
//设置camera的Z轴投射坐标,避免出现呼脸效果
mCamera.setLocation(0, 0, 100);

onDraw();

//使用Matrix
mCamera.save();
mMatrix.reset();
mCamera.rotateX(degree);
mCamera.getMatrix(mMatrix);
mCamera.restore();
​
mMatrix.preTranslate(-centerX, -centerY);
mMatrix.postTranslate(centerX, centerY);
mCanvas.concat(mMatrix);
​
mCanvas.drawXXX();
mCanvas.restore();

//直接使用canvas.translate
mCamera.save();
mCamera.retateX(degree);
mCanvas.translate(centerX, centerY);
mCamera.applyToCanvas(canvas);
mCanvas.translate(-centerX, -centerY);
mCamera.restore();
​
mCanvas.drawXXX();
mCanvas.restore();

HandlerThread简单使用

HandlerThread其实是内部建立了Looper的Thread.(新建线程是没有开启消息循环的)

注意:HandlerThread仍为普通线程,串行执行任务

private HandlerThread mHandlerThread;
private Handler mHander;
​
onCreate(){
    ...
    //创建HandlerThread,并将线程命名为:handlerThread
    mHandlerThread = new HandlerThread("handlerThread");
    mHandlerThread.start();
    mHandler = new Handler(mHandlerThread.getLooper){
        @Overtide
        public void handleMessage(Message msg){
            super.handleMessage(msg);
            //该方法运行在HandlerThread线程中,可执行耗时操作
            Log.e("Msg:", msg.what + "线程 : " + Thread.currentThread().getName());
        }
    }
  
    mHandler.sendEmptyMessage(0);
    //使用post同样可以将run()操作运行在HandlerThread中
    mHandler.post(new Runnable() {
                @Override
                public void run() {
                    Log.e("Msg:", 1 + "线程 : " + Thread.currentThread().getName());
                }
            });
  
}
​

Log:
Msg:0 线程 : handlerThread
Msg:1 线程 : handlerThread