Avoid object allocations during draw/layout operations

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint = new Paint(Paint.LINEAR_TEXT_FLAG);
    }

在自定义View中的onDraw中如果有new的对象，将会报出警告，警告如下：

Avoid object allocations during draw/layout operations (preallocate and reuse instead)

Issue: Looks for memory allocations within drawing code
Id: DrawAllocation

You should avoid allocating objects during a drawing or layout operation. These are called frequently, so a smooth UI can be interrupted by garbage collection pauses caused by the object allocations.

The way this is generally handled is to allocate the needed objects up front and to reuse them for each drawing operation.
Some methods allocate memory on your behalf (such as Bitmap.create), and these should be handled in the same way.

翻译大意就是必要在draw/layout（onDraw（）反复运行）这种频繁操作中分配对象，会导致大量new新的对象，频繁垃圾回收。
解决方法，将new对象放在构造函数中，在onDraw中进行复用：

class YourClass extends View
{
    //Paint paint = new Paint();也可以
    Paint paint;

    public YourClass(Context context) {
        this(context, null);
        init();
    }

    public YourClass(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
        init();
    }

    public YourClass(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }
    private void init()
    {
      paint = new Paint(Paint.LINEAR_TEXT_FLAG);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        paint.setColor(Color.WHITE);

stackoverflow

• Object allocation during draw/layout?