音视频开发任务（1）——绘制图片

一、ImageView设置图片的方式

1. imageView.setImageDrawable
   imageView.setImageDrawable(ContextCompat.getDrawable(getApplicationContext(),R.drawable.baby1));
   drawable中有一张图片baby.png

2. imageView.setsetImageBitmap(bitmap)
   查看该方式源码：

   public void setImageBitmap(Bitmap bm) {
           // Hacky fix to force setImageDrawable to do a full setImageDrawable
           // instead of doing an object reference comparison
           mDrawable = null;
           if (mRecycleableBitmapDrawable == null) {
               mRecycleableBitmapDrawable = new BitmapDrawable(mContext.getResources(), bm);
           } else {
               mRecycleableBitmapDrawable.setBitmap(bm);
           }
           setImageDrawable(mRecycleableBitmapDrawable);
       }

   可以看出该方法依旧时是把bitmap图像转为了drawable对象

3. imageView.setImageResource(int id)
   使用这种方式，图片必须是drawable目录下的资源，另外该方法是在UI线程中对图片读取和解析，可能会造成延迟,官方注释如下：

   /**
    * Sets a drawable as the content of this ImageView.
    * 
   This does Bitmap reading and decoding on the UI
    * thread, which can cause a latency hiccup.  If that's a concern,
    * consider using {@link #setImageDrawable(android.graphics.drawable.Drawable)} or
    * {@link #setImageBitmap(android.graphics.Bitmap)} and
    * {@link android.graphics.BitmapFactory} instead.
    *
    * @param resId the resource identifier of the drawable
    *
    * @attr ref android.R.styleable#ImageView_src
    */
   @android.view.RemotableViewMethod(asyncImpl="setImageResourceAsync")
   public void setImageResource(@DrawableRes int resId) 

二、SurfaceView绘制图片

surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder surfaceHolder) {
                Log.i(TAG,"surfaceCreated");
                if (surfaceHolder == null) {
                    return;
                }

                Paint paint = new Paint();
                paint.setAntiAlias(true);
                paint.setStyle(Paint.Style.STROKE);

                Bitmap bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.baby2);  // 获取bitmap
                //原始尺寸
                int width=bitmap.getWidth();
                int height=bitmap.getHeight();
                Log.i(TAG,"w:"+width+"  "+"h:"+height);
                //目标尺寸
                int newWidth=surfaceView.getWidth();
                int newHeigtht=surfaceView.getHeight();
                //压缩比
                float scaleWidth=(float)newWidth/width;
                float scaleHeight=(float)newHeigtht/height;
                //获取matrix
                Matrix matrix=new Matrix();
                matrix.postScale(scaleWidth,scaleHeight);
                //获取新的bitmap
                bitmap=Bitmap.createBitmap(bitmap,0,0,width,height,matrix,true);
                Canvas canvas = surfaceHolder.lockCanvas();  // 先锁定当前surfaceView的画布
                canvas.drawBitmap(bitmap, 0, 0, paint); //执行绘制操作
                surfaceHolder.unlockCanvasAndPost(canvas); // 解除锁定并显示在界面上
            }

            @Override
            public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

            }

            @Override
            public void surfaceDestroyed(SurfaceHolder surfaceHolder) {

            }
        });

三、自定义View绘制图片

1. 创建自定义View

   public class MyView extends View {
   Paint paint=new Paint();
   
   public MyView(Context context) {
       super(context);
   }
   
   public MyView(Context context, AttributeSet attrs) {
       super(context, attrs);
   }
   
   public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
       super(context, attrs, defStyleAttr);
   }
   
   @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
   public MyView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
       super(context, attrs, defStyleAttr, defStyleRes);
   
   }
   
   @Override
   protected void onDraw(Canvas canvas){
       super.onDraw(canvas);
       paint.setAntiAlias(true); // 是否抗锯齿
   
       //画圆
       //canvas.drawCircle(50,50,50,paint);
   
       //画图片
       Bitmap bitmap= BitmapFactory.decodeResource(getResources(),R.drawable.baby2);
       int width=bitmap.getWidth();
       int height=bitmap.getHeight();
       //目标尺寸
       int newWidth=300;
       int newHeigtht=200;
       //压缩比
       float scaleWidth=(float)newWidth/width;
       float scaleHeight=(float)newHeigtht/height;
       //获取matrix
       Matrix matrix=new Matrix();
       matrix.postScale(scaleWidth,scaleHeight);
       //获取新的bitmap
       bitmap=Bitmap.createBitmap(bitmap,0,0,width,height,matrix,true);
       canvas.drawBitmap(bitmap,0,0,paint);
   
   }

}

然后在XML布局文件中引入Myview即可