ActionBar的Overlay模式如何不遮盖顶部内容的问题

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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：

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TypedArray actionbarSizeTypedArray = getActivity().obtainStyledAttributes(newint[] {

        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：

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/*

 * 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 android.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 = newRect();

    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.styleable.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 = newRect(insets);

        setWillNotDraw(mInsetBackground == null);

        postInvalidateOnAnimation();

        if(mOnInsetsCallback != null) {

            mOnInsetsCallback.onInsetsChanged(insets);

        }

        returntrue;// 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？

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package com.example.drawinsetsframelayoutdemo;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import android.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 = newArrayList<Map<String, ?>>();

        for(int i = 0; i < 103; i++) {

            Map<String, String> m = newHashMap<String, String>();

            m.put("Text","Text"+ i);

            m.put("Button","Button"+ i);

            list.add(m);

        }

        SimpleAdapter adapter = newSimpleAdapter(this, list, R.layout.listitem, from, to);

        listView.setAdapter(adapter);

                                                                                                                                                                                                                          

        DrawInsetsFrameLayout drawInsetsFrameLayout = (DrawInsetsFrameLayout) findViewById(R.id.my_draw_insets_layout);

        drawInsetsFrameLayout.setOnInsetsCallback(newDrawInsetsFrameLayout.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 = newView(MainActivity.this);

                AbsListView.LayoutParams params = newAbsListView.LayoutParams(LayoutParams.FILL_PARENT, insets.top);

                                                                                                                                                                                                                                 

                headerView.setLayoutParams(params);

                headerView.setBackgroundColor(0x33000000);

                listView.addHeaderView(headerView);

            }

        });

    }

                                                                                                                                                                                                                 

}

设置actionbar风格的xml文件：

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<!-- Application theme. -->

<style name="AppTheme"parent="AppBaseTheme">

    <item name="android:actionBarStyle">@style/TranslucentActionBar</item>

    <item name="android:windowActionBarOverlay">true</item>

    <item name="android:windowTranslucentStatus">true</item>

</style>

<style name="TranslucentActionBar"parent="android:Widget.Holo.Light.ActionBar.Solid.Inverse">

    <item name="android:background">@null</item>

</style>

其中TranslucentActionBar是为DrawInsetsFrameLayout自定义的一个属性，而activity的actionbar和statusbar在这里我们都是设置成了浮动模式的，注意<item name="android:windowTranslucentStatus">true</item>。

最后是布局代码：

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<?xml version="1.0"encoding="utf-8"?>

<FrameLayout xmlns:android="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

        android:id="@+id/my_draw_insets_layout"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        yourapp:insetBackground="#9000"/>

</FrameLayout>

效果图：

-----

完整的demo代码在这里下载：http://download.csdn.net/detail/jianghejie123/7992853