Android笔记：标题栏颜色渐变效果的实现

/**
 *  @author  程龙
 *  @data  2018/12/21
 *  带滚动监听的scrollview
 */
public class GradationScrollView extends ScrollView {

    public interface ScrollViewListener {

        void onScrollChanged(GradationScrollView scrollView, int x, int y,
                             int oldx, int oldy);

    }

    private ScrollViewListener scrollViewListener = null;

    public GradationScrollView(Context context) {
        super(context);
    }

    public GradationScrollView(Context context, AttributeSet attrs,
                               int defStyle) {
        super(context, attrs, defStyle);
    }

    public GradationScrollView(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);
        }
    }

}

public class MainActivity extends Activity implements ScrollViewListener{
 
    private ObservableScrollView scrollView;
    
	private ListView listView;
	
	private ImageView imageView;
	
	private TextView textView;
	
	private int imageHeight;
 
	@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        scrollView = (ObservableScrollView) findViewById(R.id.scrollview);
        listView = (ListView) findViewById(R.id.listview);
        imageView = (ImageView) findViewById(R.id.imageview);
        textView = (TextView) findViewById(R.id.textview);
        initListeners();
        initData();
    }
	
	private void initListeners() {
		// 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);
				imageHeight = imageView.getHeight();
 
				scrollView.setScrollViewListener(MainActivity.this);
			}
		});
	}
 
 
 
	private void initData() {
		ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, getResources().getStringArray(R.array.data));
		listView.setAdapter(adapter);
	}
 
 
 
	@Override
	public void onScrollChanged(ObservableScrollView scrollView, int x, int y,
			int oldx, int oldy) {
		//这个就是关键方法了，大家可根据实际需要进行编写
		if (y <= 0) {
			textView.setBackgroundColor(Color.argb((int) 0, 227, 29, 26));
		} else if (y > 0 && y <= imageHeight) {
			float scale = (float) y / imageHeight;
			float alpha = (255 * scale);
			
			textView.setBackgroundColor(Color.argb((int) alpha, 227, 29, 26));
		} else {
			textView.setBackgroundColor(Color.argb((int) 255, 227, 29, 26));
		}
	}
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="${relativePackage}.${activityClass}" >
 
    <com.jukopro.titlebarcolor.ObservableScrollView
        android:id="@+id/scrollview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="none" >
 
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical" >
 
            <ImageView
                android:id="@+id/imageview"
                android:layout_width="match_parent"
                android:layout_height="200dp"
                android:background="@drawable/zuqiu" />
 
            <com.jukopro.titlebarcolor.MyListview
                android:id="@+id/listview"
                android:layout_width="match_parent"
                android:layout_height="wrap_content" >
            </com.jukopro.titlebarcolor.MyListview>
        </LinearLayout>
    </com.jukopro.titlebarcolor.ObservableScrollView>
 
    <TextView
        android:id="@+id/textview"
        android:layout_width="match_parent"
        android:layout_height="48dp"
        android:gravity="center"
        android:text="我是标题"
        android:textSize="18sp"
        android:textColor="@android:color/white"
        android:background="#00000000" />
 
</RelativeLayout>