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Shadow

View的大小位置都是通过x，y确定的，而在Android 5.0有了z轴的概念，这个z值就是View的高度（elevation），高度决定了阴影（shadow）的大小。

View的z值由两部分组成，elevation和translationZ；

eleavation是静态的成员，translationZ是用来做动画。

Z = elevation + translationZ

elevation的设置可以在layout中使用 android:elevation属性去定义，也可以在代码中使用 View.setElevation 方法去定义

translationZ的设置可以使用View.setTranslationZ方法，在做动画时可以通过ViewPropertyAnimator.z和ViewPropertyAnimator.translationZ方法设置；

代码：

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mImageView = (ImageView) findViewById(R.id.image);
        mImageView.setTranslationZ(100);
        mImageView.setElevation(50);
        mImageView.setOutlineProvider(mOutlineProvider);
        //mImageView.setClipToOutline(true);//裁剪
    }


    ViewOutlineProvider mOutlineProvider = new ViewOutlineProvider() {
        @Override
        public void getOutline(View view, Outline outline) {
            outline.setRect(new Rect(0, 0, mImageView.getWidth(), mImageView.getHeight()));
        }
    };

mImageView.setOutlineProvider一定要设置，在getOutline中设置Outline；

投影效果：

Clip

可以使用ViewOutlineProvider实现Outline和Clip

public class MainActivity extends Activity {
    private ImageView mImageView;
    private Rect mViewRect;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mImageView = (ImageView) findViewById(R.id.image);

        mImageView.setOutlineProvider(mOutlineProvider);
        mImageView.setClipToOutline(true);//裁剪
    }

    ViewOutlineProvider mOutlineProvider = new ViewOutlineProvider() {
        @Override
        public void getOutline(View view, Outline outline) {
            if(mViewRect != null){
                //outline.setRoundRect(mViewRect, 15);//绘制轮廓，圆角
                outline.setRect(mViewRect);
                //outline.canClip();//是否符合裁剪
            }else{
                outline.setRoundRect(new Rect(0, 0, mImageView.getWidth(), mImageView.getHeight()),15);
            }
        }
    };

    public void clickButton1(View view){
        mViewRect = new Rect(0, 0, mImageView.getWidth()/2, mImageView.getHeight());
        mImageView.invalidateOutline();
    }

    public void clickButton2(View view){
        mViewRect = new Rect(0, 0, mImageView.getWidth(), mImageView.getHeight()/2);
        mImageView.invalidateOutline();
    }

    public void clickButton3(View view){
        mViewRect = new Rect(mImageView.getWidth()/6, mImageView.getHeight()/8, mImageView.getWidth()*5/6, mImageView.getHeight()*7/8);
        mImageView.invalidateOutline();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

圆角效果以及Clip的三种效果