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Android ActionBar的Overlay模式如何不遮盖顶部内容的问题
关于actionbar的overlay模式请参考 如何让android的actionbar浮动且透明 一文。这篇文章讲的是如何在这种模式下让actionbar不遮住顶部的内容。
这 一般是这样的场景，在一个ListView显示图片的界面中，当ListView向下滑动的时候，actionbar是是浮动在GridView上面一层 的，但是当ListView滚动到顶部，顶部的内容是完全显示出来的，当然这种情况一般ActionBar我们会做成透明效果。
其实很多人都能想到的是，将ListView加上一个高度和actionbar的高度相同的header不就行了吗？
但是，难点是如何得到actionbar的高度。
actionbar的高度其实是在android系统主题的资源文件中定义的，如果你没有主动去修改actionbar的高度，那么可以通过下面的代码来获取：
TypedArray actionbarSizeTypedArray = getActivity().obtainStyledAttributes(new int[] { android.R.attr.actionBarSize});float h = actionbarSizeTypedArray.getDimension(0, 0);
但是这种方式并不太规范，而且在android4.4之后，statusbar所在的区域也是可以显示内容的，这时你还得去计算statusbar的高度。
其 实FrameLayout 中boolean fitSystemWindows(Rect insets)方法的insets参数就包含了非内容区域的高度。fitSystemWindows会在加载的时候被调用，如果我们在ListView重 写fitSystemWindows不就可以知道该给ListView添加多高的HeaderView了吗？
但是一般我们不希望这样用 ListView，因为使用重写的ListView的几率实在太大了（下拉刷新ListView等），而采取另外的方法，把ListView和一个重写了 fitSystemWindows方法的FrameLayout放在同一个FrameLayout中，然后通过回调的方式来通知ListView已经获取 到了actionbar（或者+statusbar）的高度了。
我们将这个实现了fitSystemWindows方法的FrameLayout命名为：DrawInsetsFrameLayout
代码如下：
/* * Copyright 2014 Google Inc. * * 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.drawinsetsframelayoutdemo;import <span style="width: auto; height: auto; float: none;" id="6_nwp"><a style="text-decoration: none;" mpid="6" target="_blank" href=http://www.mamicode.com/"http://cpro.baidu.com/cpro/ui/uijs.php?rs=1&u=http%3A%2F%2Fwww%2Ejcodecraeer%2Ecom%2Fa%2Fanzhuokaifa%2Fandroidkaifa%2F2014%2F0930%2F1720%2Ehtml&p=baidu&c=news&n=10&t=tpclicked3_hc&q=01072140_cpr&k=android&k0=android&kdi0=8&k1=style&kdi1=8&sid=1591b71c7abd51a3&ch=0&tu=u1921070&jk=3064ed901c653638&cf=29&rb=0&fv=16&stid=9&urlid=0&luki=1&seller_id=1&di=128" id="6_nwl"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">android</span></a></span>.content.Context;import android.content.res.TypedArray;import android.graphics.Canvas;import android.graphics.Rect;import android.graphics.drawable.Drawable;import android.util.AttributeSet;import android.widget.FrameLayout;/** * A layout that draws something in the insets passed to {@link #fitSystemWindows(Rect)}, i.e. the area above UI chrome * (status and navigation bars, overlay action bars). */public class DrawInsetsFrameLayout extends FrameLayout { private Drawable mInsetBackground; private Rect mInsets; private Rect mTempRect = new Rect(); private OnInsetsCallback mOnInsetsCallback; public DrawInsetsFrameLayout(Context context) { super(context); init(context, null, 0); } public DrawInsetsFrameLayout(Context context, AttributeSet attrs) { super(context, attrs); init(context, attrs, 0); } public DrawInsetsFrameLayout(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(context, attrs, defStyle); } private void init(Context context, AttributeSet attrs, int defStyle) { final TypedArray a = context.obtainStyledAttributes(attrs, R.<span style="width: auto; height: auto; float: none;" id="7_nwp"><a style="text-decoration: none;" mpid="7" target="_blank" href=http://www.mamicode.com/"http://cpro.baidu.com/cpro/ui/uijs.php?rs=1&u=http%3A%2F%2Fwww%2Ejcodecraeer%2Ecom%2Fa%2Fanzhuokaifa%2Fandroidkaifa%2F2014%2F0930%2F1720%2Ehtml&p=baidu&c=news&n=10&t=tpclicked3_hc&q=01072140_cpr&k=style&k0=android&kdi0=8&k1=style&kdi1=8&sid=1591b71c7abd51a3&ch=0&tu=u1921070&jk=3064ed901c653638&cf=29&rb=0&fv=16&stid=9&urlid=0&luki=2&seller_id=1&di=128" id="7_nwl"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">style</span></a></span>able.DrawInsetsFrameLayout, defStyle, 0); if (a == null) { return; } mInsetBackground = a.getDrawable(R.styleable.DrawInsetsFrameLayout_insetBackground); a.recycle(); setWillNotDraw(true); } @Override protected boolean fitSystemWindows(Rect insets) { mInsets = new Rect(insets); setWillNotDraw(mInsetBackground == null); postInvalidateOnAnimation(); if (mOnInsetsCallback != null) { mOnInsetsCallback.onInsetsChanged(insets); } return true; // consume insets } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); int width = getWidth(); int height = getHeight(); if (mInsets != null && mInsetBackground != null) { // Top mTempRect.set(0, 0, width, mInsets.top); mInsetBackground.setBounds(mTempRect); mInsetBackground.draw(canvas); // Bottom mTempRect.set(0, height - mInsets.bottom, width, height); mInsetBackground.setBounds(mTempRect); mInsetBackground.draw(canvas); // Left mTempRect.set(0, mInsets.top, mInsets.left, height - mInsets.bottom); mInsetBackground.setBounds(mTempRect); mInsetBackground.draw(canvas); // Right mTempRect.set(width - mInsets.right, mInsets.top, width, height - mInsets.bottom); mInsetBackground.setBounds(mTempRect); mInsetBackground.draw(canvas); } } @Override protected void onAttachedToWindow() { super.onAttachedToWindow(); if (mInsetBackground != null) { mInsetBackground.setCallback(this); } } @Override protected void onDetachedFromWindow() { super.onDetachedFromWindow(); if (mInsetBackground != null) { mInsetBackground.setCallback(null); } } /** * Allows the calling container to specify a callback for custom processing when insets change (i.e. when * {@link #fitSystemWindows(Rect)} is called. This is useful for setting padding on UI elements based on * UI chrome insets (e.g. a Google Map or a ListView). When using with ListView or GridView, remember to set * clipToPadding to false. */ public void setOnInsetsCallback(OnInsetsCallback onInsetsCallback) { mOnInsetsCallback = onInsetsCallback; } public static interface OnInsetsCallback { public void onInsetsChanged(Rect insets); }}
其中最主要的就是fitSystemWindows方法，其他的不过是绘制DrawInsetsFrameLayout在actionbar部分的显示颜色而已。
如何使用DrawInsetsFrameLayout呢？
package com.example.drawinsetsframelayoutdemo;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import <span style="width: auto; height: auto; float: none;" id="5_nwp"><a style="text-decoration: none;" mpid="5" target="_blank" href=http://www.mamicode.com/"http://cpro.baidu.com/cpro/ui/uijs.php?rs=1&u=http%3A%2F%2Fwww%2Ejcodecraeer%2Ecom%2Fa%2Fanzhuokaifa%2Fandroidkaifa%2F2014%2F0930%2F1720%2Ehtml&p=baidu&c=news&n=10&t=tpclicked3_hc&q=01072140_cpr&k=android&k0=android&kdi0=8&k1=style&kdi1=8&sid=1591b71c7abd51a3&ch=0&tu=u1921070&jk=3064ed901c653638&cf=29&rb=0&fv=16&stid=9&urlid=0&luki=1&seller_id=1&di=128" id="5_nwl"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">android</span></a></span>.app.Activity;import android.graphics.Rect;import android.graphics.drawable.ColorDrawable;import android.os.Bundle;import android.util.Log;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.Window;import android.view.ViewGroup.LayoutParams;import android.widget.AbsListView;import android.widget.ListView;import android.widget.SimpleAdapter;public class MainActivity extends Activity { private ListView listView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView= (ListView) findViewById(R.id.listview); String[] from = { "Text", "Button" }; int[] to = { R.id.text, R.id.button }; List<Map<String, ?>> list = new ArrayList<Map<String, ?>>(); for (int i = 0; i < 103; i++) { Map<String, String> m = new HashMap<String, String>(); m.put("Text", "Text" + i); m.put("Button", "Button" + i); list.add(m); } SimpleAdapter adapter = new SimpleAdapter(this, list, R.layout.listitem, from, to); listView.setAdapter(adapter); DrawInsetsFrameLayout drawInsetsFrameLayout = (DrawInsetsFrameLayout) findViewById(R.id.my_draw_insets_layout); drawInsetsFrameLayout.setOnInsetsCallback(new DrawInsetsFrameLayout.OnInsetsCallback() { @Override public void onInsetsChanged(Rect insets) { // Update the map padding (inset the compass, zoom buttons, attribution, etc.) Log.i("", "insets.top = " + insets.top); View headerView = new View(MainActivity.this); AbsListView.LayoutParams params = new AbsListView.LayoutParams(LayoutParams.FILL_PARENT, insets.top); headerView.setLayoutParams(params); headerView.setBackgroundColor(0x33000000); listView.addHeaderView(headerView); } }); } }
设置actionbar风格的xml文件：
<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:<span style="width: auto; height: auto; float: none;" id="1_nwp"><a style="text-decoration: none;" mpid="1" target="_blank" href=http://www.mamicode.com/"http://cpro.baidu.com/cpro/ui/uijs.php?rs=1&u=http%3A%2F%2Fwww%2Ejcodecraeer%2Ecom%2Fa%2Fanzhuokaifa%2Fandroidkaifa%2F2014%2F0930%2F1720%2Ehtml&p=baidu&c=news&n=10&t=tpclicked3_hc&q=01072140_cpr&k=android&k0=android&kdi0=8&k1=style&kdi1=8&sid=1591b71c7abd51a3&ch=0&tu=u1921070&jk=3064ed901c653638&cf=29&rb=0&fv=16&stid=9&urlid=0&luki=1&seller_id=1&di=128" id="1_nwl"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">android</span></a></span>="http://schemas.android.com/apk/res/android" xmlns:yourapp="http://schemas.android.com/apk/res-auto" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ListView android:id="@+id/listview" android:layout_width="match_parent" android:layout_height="match_parent" /> <com.example.drawinsetsframelayoutdemo.DrawInsetsFrameLayout <span style="width: auto; height: auto; float: none;" id="2_nwp"><a style="text-decoration: none;" mpid="2" target="_blank" href=http://www.mamicode.com/"http://cpro.baidu.com/cpro/ui/uijs.php?rs=1&u=http%3A%2F%2Fwww%2Ejcodecraeer%2Ecom%2Fa%2Fanzhuokaifa%2Fandroidkaifa%2F2014%2F0930%2F1720%2Ehtml&p=baidu&c=news&n=10&t=tpclicked3_hc&q=01072140_cpr&k=android&k0=android&kdi0=8&k1=style&kdi1=8&sid=1591b71c7abd51a3&ch=0&tu=u1921070&jk=3064ed901c653638&cf=29&rb=0&fv=16&stid=9&urlid=0&luki=1&seller_id=1&di=128" id="2_nwl"><span style="color:#0000ff;font-size:14px;width:auto;height:auto;float:none;">android</span></a></span>:id="@+id/my_draw_insets_layout" android:layout_width="match_parent" android:layout_height="match_parent" yourapp:insetBackground="#9000" /></FrameLayout>
效果图：
Android ActionBar的Overlay模式如何不遮盖顶部内容的问题
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