android仿知乎ScrollView滚动改变标题栏透明度

import com.example.d_changealphabyscroll.widget.ObservableScrollView;import com.example.d_changealphabyscroll.widget.ObservableScrollView.ScrollViewListener; import android.app.Activity;import android.graphics.Color;import android.os.Bundle;import android.util.Log;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.ViewTreeObserver;import android.view.ViewTreeObserver.OnGlobalLayoutListener;import android.webkit.WebSettings;import android.webkit.WebView;import android.webkit.WebViewClient;import android.widget.ImageView;import android.widget.ScrollView; public class MainActivity extends Activity implements ScrollViewListener{  private View layoutHead; private ObservableScrollView scrollView; private ImageView imageView; private WebView webView;  private int height ;  @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main);  initView(); }   private void initView() { webView = (WebView) findViewById(R.id.webview1); scrollView = (ObservableScrollView) findViewById(R.id.scrollview); layoutHead = findViewById(R.id.view_head); imageView = (ImageView) findViewById(R.id.imageView1); layoutHead.setBackgroundColor(Color.argb(0, 0xfd, 0x91, 0x5b));  //初始化webview //启用支持javascript  WebSettings settings = webView.getSettings();  settings.setJavaScriptEnabled(true);  webView.loadUrl("http://www.topit.me/");  //覆盖WebView默认使用第三方或系统默认浏览器打开网页的行为，使网页用WebView打开  webView.setWebViewClient(new WebViewClient(){   @Override  public boolean shouldOverrideUrlLoading(WebView view, String url) {    //返回值是true的时候控制去WebView打开，为false调用系统浏览器或第三方浏览器    view.loadUrl(url);   return true;  }  });   //获取顶部图片高度后，设置滚动监听 ViewTreeObserver vto = imageView.getViewTreeObserver();   vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {   @Override    public void onGlobalLayout() {    imageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);    height = imageView.getHeight();    imageView.getWidth();        scrollView.setScrollViewListener(MainActivity.this);   }   });       }   @Override public void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy) { // Log.i("TAG","y--->"+y+" height-->"+height); if(y<=height){ float scale =(float) y /height; float alpha = (255 * scale);// Log.i("TAG","alpha--->"+alpha);  //layout全部透明// layoutHead.setAlpha(scale);  //只是layout背景透明(仿知乎滑动效果) layoutHead.setBackgroundColor(Color.argb((int) alpha, 0xfd, 0x91, 0x5b)); }  }}

import android.content.Context;import android.util.AttributeSet;import android.widget.ScrollView;/** * 带滚动监听的scrollview * */public class ObservableScrollView extends ScrollView {  public interface ScrollViewListener {  void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy);  }  private ScrollViewListener scrollViewListener = null;  public ObservableScrollView(Context context) { super(context); }  public ObservableScrollView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); }  public ObservableScrollView(Context context, AttributeSet attrs) { super(context, attrs); }  public void setScrollViewListener(ScrollViewListener scrollViewListener) { this.scrollViewListener = scrollViewListener; }  @Override protected void onScrollChanged(int x, int y, int oldx, int oldy) { super.onScrollChanged(x, y, oldx, oldy); if (scrollViewListener != null) { scrollViewListener.onScrollChanged(this, x, y, oldx, oldy); } } }