Android滑动组件悬浮固定在顶部效果

本文实例为大家分享了Android滑动组件悬浮固定在顶部效果的具体代码，供大家参考，具体内容如下

要想实现的效果是如下：

场景：有些时候是内容中间的组件当滑动至顶部的时候固定显示在顶部。

实现的思路：

1.目标组件（button）有两套，放在顶部和内容中间；

2.当内容中间的组件滑动至顶部栏位置时控制显示/隐藏顶部和中间的组件（涉及到组件获取在屏幕的位置知识点）；

activity代码：

public class MainActivity extends AppCompatActivity implements ObservableScrollView.ScrollViewListener {
private ObservableScrollView scrollView;
private Button topBtn1, topBtn2, middleBtn1, middleBtn2;
private View topPanel, middlePanel;
private int topHeight;

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 initViews();
 initListeners();

}

@Override
public void onWindowFocusChanged(boolean hasFocus) {
 super.onWindowFocusChanged(hasFocus);

Rect frame = new Rect();
 getWindow().getDecorView().getWindowVisibleDisplayFrame(frame);
 int statusBarHeight = frame.top;//状态栏高度

int titleBarHeight = getWindow().findViewById(Window.ID_ANDROID_CONTENT).getTop();//标题栏高度
 topHeight = titleBarHeight + statusBarHeight;
}

private void initViews() {
 scrollView = (ObservableScrollView) findViewById(R.id.scrollView);
 topPanel = findViewById(R.id.topPanel);
 topBtn1 = (Button) topPanel.findViewById(R.id.button1);
 topBtn2 = (Button) topPanel.findViewById(R.id.button2);

middlePanel = findViewById(R.id.middlePanel);
 middleBtn1 = (Button) middlePanel.findViewById(R.id.button1);
 middleBtn2 = (Button) middlePanel.findViewById(R.id.button2);

}

private void initListeners() {
 topBtn1.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View view) {
   middleBtn1.setBackgroundColor(Color.WHITE);
   topBtn1.setBackgroundColor(Color.WHITE);
  }
 });

middleBtn1.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View view) {
   middleBtn1.setBackgroundColor(Color.BLUE);
   topBtn1.setBackgroundColor(Color.BLUE);
  }
 });

scrollView.setScrollViewListener(this);

}

@Override
public void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy) {
 int[] location = new int[2];
 middleBtn1.getLocationOnScreen(location);
 int locationY = location[1];
 Log.e("locationY", locationY + " " + "topHeight的值是：" + topHeight);

if (locationY <= topHeight && (topPanel.getVisibility() == View.GONE || topPanel.getVisibility() == View.INVISIBLE)) {
  topPanel.setVisibility(View.VISIBLE);
 }

if (locationY > topHeight && topPanel.getVisibility() == View.VISIBLE) {
  topPanel.setVisibility(View.GONE);
 }

}
}

要点解析：

1.在onWindowFocusChanged()方法中获取屏幕状态栏和标题栏的高度（在onCreate()方法中是获取是0）；

2.因为布局中的ScrollView的onScrollChangeListener()方法低版本API不支持——>所以activity实现了自定义ScrollView中的onScrollChanged()接口方法——>在此方法中实现组件的显示/隐藏；

自定义ScrollView的代码：

public class ObservableScrollView extends ScrollView {

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);
 }
}

public interface ScrollViewListener {

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

}
}

然后是布局文件：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.administrator.slideholdapp.MainActivity">

<com.example.administrator.slideholdapp.ObservableScrollView
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:id="@+id/scrollView">

<LinearLayout
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:orientation="vertical">

<TextView
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:layout_marginBottom="30dp"
   android:text="@string/content" />

<include android:id="@+id/middlePanel" layout="@layout/middle_item_layout"></include>

<TextView
   android:layout_width="match_parent"
   android:layout_height="wrap_content"
   android:layout_marginTop="30dp"
   android:text="@string/content" />

</LinearLayout>

</com.example.administrator.slideholdapp.ObservableScrollView>

<include android:id="@+id/topPanel" layout="@layout/middle_item_layout" android:visibility="gone"/>
</FrameLayout>