要想實現(xiàn)的效果是如下：
場景：有些時候是內(nèi)容中間的組件當(dāng)滑動至頂部的時候固定顯示在頂部。
實現(xiàn)的思路：
1.目標(biāo)組件（button）有兩套，放在頂部和內(nèi)容中間；
2.當(dāng)內(nèi)容中間的組件滑動至頂部欄位置時控制顯示/隱藏頂部和中間的組件（涉及到組件獲取在屏幕的位置知識點）；
activity代碼：
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;//狀態(tài)欄高度 int titleBarHeight = getWindow().findViewById(Window.ID_ANDROID_CONTENT).getTop();//標(biāo)題欄高度 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); } } } 要點解析：
1.在onWindowFocusChanged()方法中獲取屏幕狀態(tài)欄和標(biāo)題欄的高度（在onCreate()方法中是獲取是0）；
2.因為布局中的ScrollView的onScrollChangeListener()方法低版本API不支持――>所以activity實現(xiàn)了自定義ScrollView中的onScrollChanged()接口方法――>在此方法中實現(xiàn)組件的顯示/隱藏；
自定義ScrollView的代碼：
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>
以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持武林網(wǎng)。
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