转自：http://www.eoeandroid.com/thread-577241-1-1.html
最近看到最美等应用里面有一个特效，自己上网查了下，写了个demo如下：
在写这个demo之前，查了很多资料，主要是参考github上面的一个例子：
https://github.com/ksoichiro/Android-ObservableScrollView
这个例子里面写了很多特效，但是下载下来后，导入Studio里面很多错误，无法跑起来，所以，自己抠了其中的一个特效，修改了一些代码，效果如上图所示。
主要代码片段：（后面会有解释）
import android.content.res.TypedArray;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.util.TypedValue;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;
import com.nineoldandroids.view.ViewHelper;
public class MainActivity extends ActionBarActivity implements ObservableScrollViewCallbacks{
private static final float MAX_TEXT_SCALE_DELTA = 0.3f;
private static final boolean TOOLBAR_IS_STICKY = true;
private View mToolbar;
private View mImageView;
private View mOverlayView;
private ObservableScrollView mScrollView;
private TextView mTitleView;
private View mFab;
private int mActionBarSize;
private int mFlexibleSpaceShowFabOffset;
private int mFlexibleSpaceImageHeight;
private int mToolbarColor;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setSupportActionBar((Toolbar) findViewById(R.id.toolbar));
mFlexibleSpaceImageHeight = getResources().getDimensionPixelSize(R.dimen.flexible_space_image_height);
mActionBarSize = getActionBarSize();
mToolbarColor = getResources().getColor(R.color.primary);
mToolbar = findViewById(R.id.toolbar);
if (!TOOLBAR_IS_STICKY) {
mToolbar.setBackgroundColor(Color.TRANSPARENT);
}
mImageView = findViewById(R.id.image);
mOverlayView = findViewById(R.id.overlay);
mScrollView = (ObservableScrollView) findViewById(R.id.scroll);
mScrollView.setScrollViewCallbacks(this);
mTitleView = (TextView) findViewById(R.id.title);
mTitleView.setText(getTitle());
setTitle(null);
ScrollUtils.addOnGlobalLayoutListener(mScrollView, new Runnable() {
@Override
public void run() {
mScrollView.scrollTo(0, mFlexibleSpaceImageHeight - mActionBarSize);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
return super.onOptionsItemSelected(item);
}
protected int getActionBarSize() {
TypedValue typedValue = new TypedValue();
int[] textSizeAttr = new int[]{R.attr.actionBarSize};
int indexOfAttrTextSize = 0;
TypedArray a = obtainStyledAttributes(typedValue.data, textSizeAttr);
int actionBarSize = a.getDimensionPixelSize(indexOfAttrTextSize, -1);
a.recycle();
return actionBarSize;
}
@Override
public void onScrollChanged(int scrollY, boolean firstScroll, boolean dragging) {
float flexibleRange = mFlexibleSpaceImageHeight - mActionBarSize;
int minOverlayTransitionY = mActionBarSize - mOverlayView.getHeight();
ViewHelper.setTranslationY(mOverlayView, ScrollUtils.getFloat(-scrollY, minOverlayTransitionY, 0));
ViewHelper.setTranslationY(mImageView, ScrollUtils.getFloat(-scrollY / 2, minOverlayTransitionY, 0));
// Change alpha of overlay
ViewHelper.setAlpha(mOverlayView, ScrollUtils.getFloat((float) scrollY / flexibleRange, 0, 1));
// Scale title text
float scale = 1 + ScrollUtils.getFloat((flexibleRange - scrollY) / flexibleRange, 0, MAX_TEXT_SCALE_DELTA);
ViewHelper.setPivotX(mTitleView, 0);
ViewHelper.setPivotY(mTitleView, 0);
ViewHelper.setScaleX(mTitleView, scale);
ViewHelper.setScaleY(mTitleView, scale);
// Translate title text
int maxTitleTranslationY = (int) (mFlexibleSpaceImageHeight - mTitleView.getHeight() * scale);
int titleTranslationY = maxTitleTranslationY - scrollY;
if (TOOLBAR_IS_STICKY) {
titleTranslationY = Math.max(0, titleTranslationY);
}
ViewHelper.setTranslationY(mTitleView, titleTranslationY);
if (TOOLBAR_IS_STICKY) {
// Change alpha of toolbar background
if (-scrollY + mFlexibleSpaceImageHeight <= mActionBarSize) {
mToolbar.setBackgroundColor(ScrollUtils.getColorWithAlpha(1, mToolbarColor));
} else {
mToolbar.setBackgroundColor(ScrollUtils.getColorWithAlpha(0, mToolbarColor));
}
} else {
// Translate Toolbar
if (scrollY < mFlexibleSpaceImageHeight) {
ViewHelper.setTranslationY(mToolbar, 0);
} else {
ViewHelper.setTranslationY(mToolbar, -scrollY);
}
}
}
@Override
public void onDownMotionEvent() {
}
@Override
public void onUpOrCancelMotionEvent(ScrollState scrollState) {
}
}
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activity_main.xml文件
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="@+id/image"
android:layout_width="match_parent"
android:layout_height="@dimen/flexible_space_image_height"
android:scaleType="centerCrop"
android:src="@mipmap/ic_pic" />
<View
android:id="@+id/overlay"
android:layout_width="match_parent"
android:layout_height="@dimen/flexible_space_image_height"
android:background="?attr/colorPrimary" />
<com.picasso.observablescrollviewdemo.ObservableScrollView
android:id="@+id/scroll"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:overScrollMode="never"
android:scrollbars="none">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<View
android:layout_width="match_parent"
android:layout_height="@dimen/flexible_space_image_height"
android:background="@android:color/transparent" />
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/white"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:text="@string/desc" />
</LinearLayout>
</com.picasso.observablescrollviewdemo.ObservableScrollView>
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?attr/colorPrimary"
android:minHeight="?attr/actionBarSize"
app:popupTheme="@style/Theme.AppCompat.Light.DarkActionBar"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
>
<TextView
android:id="@+id/title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ellipsize="end"
android:gravity="center_vertical"
android:maxLines="1"
android:minHeight="?attr/actionBarSize"
android:textColor="@android:color/white"
android:text="Make Attractive"
android:paddingLeft="@dimen/activity_vertical_margin"
android:textSize="20sp" />
<View
android:layout_width="match_parent"
android:layout_height="@dimen/flexible_space_image_height"
android:background="@android:color/transparent" />
</LinearLayout>
</FrameLayout>
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其实，效果实现很简单，控件ObservableScrollView主要是继承了ScrollView并实现了Scrollable接口，在MainActivity中，重写onScrollChanged方法，在方法中，主要做了这几部操作：
1、随着滑动，让图片mImageView上移
2、随着滑动，让盖在图片上的view上移，长度是imageView上移的2倍
3、随着滑动，让盖在图片上的view的alpha值逐渐变大（就是那个渐渐变绿的效果）
4、随着滑动，让Title的字体逐渐变小并让title上移到ToolBar的位置
5、当滑动到ToolBar的位置时，让ToolBar显示
下载源码如下：
ObservableScrollViewDemo.rar