我在 Android API 中看到了以下示例：
/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.example.android.apis.view;
import com.example.android.apis.R;
import android.app.ListActivity;
import android.content.Context;
import android.graphics.PixelFormat;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.view.LayoutInflater;
import android.view.WindowManager;
import android.view.WindowManager.LayoutParams;
import android.widget.AbsListView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
/**
* Another variation of the list of cheeses. In this case, we use
* {@link AbsListView#setOnScrollListener(AbsListView.OnScrollListener)
* AbsListView#setOnItemScrollListener(AbsListView.OnItemScrollListener)} to display the
* first letter of the visible range of cheeses.
*/
public class List9 extends ListActivity implements ListView.OnScrollListener {
private final class RemoveWindow implements Runnable {
public void run() {
removeWindow();
}
}
private RemoveWindow mRemoveWindow = new RemoveWindow();
Handler mHandler = new Handler();
private WindowManager mWindowManager;
private TextView mDialogText;
private boolean mShowing;
private boolean mReady;
private char mPrevLetter = Character.MIN_VALUE;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mWindowManager = (WindowManager)getSystemService(Context.WINDOW_SERVICE);
// Use an existing ListAdapter that will map an array
// of strings to TextViews
setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, mStrings));
getListView().setOnScrollListener(this);
LayoutInflater inflate = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
mDialogText = (TextView) inflate.inflate(R.layout.list_position, null);
mDialogText.setVisibility(View.INVISIBLE);
mHandler.post(new Runnable() {
public void run() {
mReady = true;
WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT,
WindowManager.LayoutParams.TYPE_APPLICATION,
WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE
| WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
PixelFormat.TRANSLUCENT);
mWindowManager.addView(mDialogText, lp);
}});
}
@Override
protected void onResume() {
super.onResume();
mReady = true;
}
@Override
protected void onPause() {
super.onPause();
removeWindow();
mReady = false;
}
@Override
protected void onDestroy() {
super.onDestroy();
mWindowManager.removeView(mDialogText);
mReady = false;
}
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
if (mReady) {
char firstLetter = mStrings[firstVisibleItem].charAt(0);
if (!mShowing && firstLetter != mPrevLetter) {
mShowing = true;
mDialogText.setVisibility(View.VISIBLE);
}
mDialogText.setText(((Character)firstLetter).toString());
mHandler.removeCallbacks(mRemoveWindow);
mHandler.postDelayed(mRemoveWindow, 3000);
mPrevLetter = firstLetter;
}
}
public void onScrollStateChanged(AbsListView view, int scrollState) {
}
private void removeWindow() {
if (mShowing) {
mShowing = false;
mDialogText.setVisibility(View.INVISIBLE);
}
}
private String[] mStrings = Cheeses.sCheeseStrings;
}
有谁知道如何使显示当前字母的窗口仅在用户滚动时出现？目前，活动开始后至少需要 3-4 秒才能消失。