安卓获取输入法高度与ViewTreeObserver讲解

为了方便部分精力少的朋友，本文开始就直接介绍安卓获取输入法高度的方法，然后再逐步讲解。

安卓获取输入法高度

前言

在某些场景下， 比如写一个聊天界面，包括输入框和发送以及上面的消息列表，简单的使用LinearLayout或者RelativeLayout布局，当点击输入框，键盘弹起后，通常是不会遮挡输入框和发送的（有时就比较蛋疼了，不知为啥，它就是遮挡），因为它们也随键盘弹了起来。但布局再复杂点，比如说再加个表情栏或者更多栏，这样你肯定要手动控制输入框的高度了。因此，你就必须手动控制输入框的升降，但问题是升多高呢？？？这时，就要想办法获取输入法高度了(～￣▽￣)～

由于目前安卓上还没有提供直接获取输入法高度的api，因此只好我们自己想办法获取它的高度了。

注：此思路由国外一大神提出，附上他的 Github ;

清单

这里有两个文件：

interface KeyboardHeightObserver
class KeyboardHeightProvider

前一个用在待观测页面的作为回调函数，后面是主要的方法所在的类了。

开始

文章后面会附上源码，引入这两个文件后，在要获取输入法高度的页面，首先实现接口KeyboardHeightObserver，即第一个文件，并重写里面的方法；

然后再定义变量 KeyboardHeightProvider keyboardHeightProvider;
实例化

     /**
     * Construct a new KeyboardHeightProvider
     *
     * @param activity The parent activity
     * @param layoutId   R.layout.*
     */
       // 以上为构造函数的相关注释，当然这里是我修改的，这样可以同时支持观测多个页面
       keyboardHeightProvider = new KeyboardHeightProvider(this, R.layout.activity_chat);

       new Handler().post(new Runnable() {
            @Override
            public void run() {
                keyboardHeightProvider.start();
            }
        });

这时还要在onStart()函数里面加上 keyboardHeightProvider.setKeyboardHeightObserver(this); 即：

    @Override
    public void onStart() {
        super.onStart();
        // 这里使用了刚才实现的接口
        keyboardHeightProvider.setKeyboardHeightObserver(this);
    }

考虑更全的话，还可以加上以下语句：

    @Override
    public void onPause() {
        super.onPause();
        keyboardHeightProvider.setKeyboardHeightObserver(null);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        keyboardHeightProvider.close();
    }

这样一来，在回调函数 onKeyboardHeightChanged里面就回收到回调结果了，大功告成！

ViewTreeObserver讲解

这里就结合上面输入法的例子，讲讲ViewTreeObserver。

获取输入法高度原理

思路

在要获取输入法高度的页面，创建一个看不见的弹窗，即宽为0，高为全屏，并为弹窗设置全局布局监听器。当布局有变化，比如有输入法弹窗出现或消失时，监听器回调函数就会被调用。而其中的关键就是当输入法弹出时，它会把之前我们创建的那个看不见的弹窗往上挤，这样我们创建的那个弹窗的位置就变化了，只要获取它底部高度的变化值就可以间接的获取输入法的高度了。

实现

首先创建类KeyboardHeightProvider，继承自PopupWindow；

然后构造器内完成相关初始化：


        super(activity);
        this.activity = activity;

       LayoutInflater inflator = (LayoutInflater) activity.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        this.popupView = inflator.inflate(layoutId, null, false);
        setContentView(popupView);

        setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_RESIZE | WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);
        setInputMethodMode(PopupWindow.INPUT_METHOD_NEEDED);

        parentView = activity.findViewById(android.R.id.content);

        // 设置宽高
        setWidth(0);
        setHeight(WindowManager.LayoutParams.MATCH_PARENT);

然后就是重点，为popupView的观测者（感觉用 ViewTreeObserver还是更合适）设置全局布局监听器

        popupView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                if (popupView != null) {
                    handleOnGlobalLayout();
                }
            }
        });

其中handleOnGlobalLayout函数功能则是：获取弹窗高度，并作差得出输入法高度，以及通知回调。

    /**
     * Popup window itself is as big as the window of the Activity.
     * The keyboard can then be calculated by extracting the popup view bottom
     * from the activity window height.
     */
    private void handleOnGlobalLayout() {

        Point screenSize = new Point();
        activity.getWindowManager().getDefaultDisplay().getSize(screenSize);

        Rect rect = new Rect();
        popupView.getWindowVisibleDisplayFrame(rect);

        // REMIND, you may like to change this using the fullscreen size of the phone
        // and also using the status bar and navigation bar heights of the phone to calculate
        // the keyboard height. But this worked fine on a Nexus.
        int orientation = getScreenOrientation();
        int keyboardHeight = screenSize.y - rect.bottom;

        if (keyboardHeight == 0) {
            notifyKeyboardHeightChanged(0, orientation);
        }
        else if (orientation == Configuration.ORIENTATION_PORTRAIT) {
            this.keyboardPortraitHeight = keyboardHeight;
            notifyKeyboardHeightChanged(keyboardPortraitHeight, orientation);
        }
        else {
            this.keyboardLandscapeHeight = keyboardHeight;
            notifyKeyboardHeightChanged(keyboardLandscapeHeight, orientation);
        }
    }

嗯，大概就是这样(*￣3￣)╭

关于ViewTreeObserver

定义

首先自然要给出官方的定义：

/**
 * A view tree observer is used to register listeners that can be notified of global
 * changes in the view tree. Such global events include, but are not limited to,
 * layout of the whole tree, beginning of the drawing pass, touch mode change....
 *
 * A ViewTreeObserver should never be instantiated by applications as it is provided
 * by the views hierarchy. Refer to {@link android.view.View#getViewTreeObserver()}
 * for more information.
 */

翻译过来大概是

// 原谅我英语不好（╯︿╰）， 不过我发现谷歌翻译的效果还是不错的

/**
* 视图树观察器用于注册可以在视图树中通知全局
* 更改的侦听器。此类全局事件包括但不限于
* 整个树的布局，绘图过程的开始，触摸模式更改.... 
* 
* ViewTreeObserver永远不应由应用程序实例化，因为它由视图层次结构提供
* 。有关更多信息，请参阅{@link android.view.View＃getViewTreeObserver（）}
* 。 
*/

继承

java.lang.Object
       android.view.ViewTreeObserver

直接继承自Object，没有另外的继承关系

摘要

Nested Classes
interface	ViewTreeObserver.OnDrawListener	Interface definition for a callback to be invoked when the view tree is about to be drawn.
interface	ViewTreeObserver.OnGlobalFocusChangeListener	Interface definition for a callback to be invoked when the focus state within the view tree changes.
interface	ViewTreeObserver.OnGlobalLayoutListener	Interface definition for a callback to be invoked when the global layout state or the visibility of views within the view tree changes.
interface	ViewTreeObserver.OnPreDrawListener	Interface definition for a callback to be invoked when the view tree is about to be drawn.
interface	ViewTreeObserver.OnScrollChangedListener	Interface definition for a callback to be invoked when something in the view tree has been scrolled.
interface	ViewTreeObserver.OnTouchModeChangeListener	Interface definition for a callback to be invoked when the touch mode changes.

另外方法挺多的，我就不列举了。

获取View高度的三种方法

注：此处参考了小马快跑 的博客

在某些时候，我们要获取view的高度，但获取到的为0，为什么呢？这样通常时由于页面还未测量导致的，比如在onCreate中调用的话就会直接返回0。这是就需要我们手动获取了。

View的MeasureSpec.UNSPECIFIED

通过设置View的MeasureSpec.UNSPECIFIED来测量：

int w = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
int h = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
view.measure(w, h);
//获得宽高
int viewWidth=view.getMeasuredWidth();
int viewHeight=view.getMeasuredHeight();

设置我们的SpecMode为UNSPECIFIED，然后去调用onMeasure测量宽高，就可以得到宽高。

ViewTreeObserver .addOnGlobalLayoutListener

通过ViewTreeObserver .addOnGlobalLayoutListener来获得宽高，当获得正确的宽高后，请移除这个观察者，否则回调会多次执行：

//获得ViewTreeObserver 
ViewTreeObserver observer=view.getViewTreeObserver();
//注册观察者，监听变化
observer.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
     @Override
     public void onGlobalLayout() {
            //判断ViewTreeObserver 是否alive，如果存活的话移除这个观察者
           if(observer.isAlive()){
             observer.removeGlobalOnLayoutListener(this);
             //获得宽高
             int viewWidth=view.getMeasuredWidth();
             int viewHeight=view.getMeasuredHeight();
           }
        }
   });

ViewTreeObserver .addOnPreDrawListener

通过ViewTreeObserver .addOnPreDrawListener来获得宽高，在执行onDraw之前已经执行了onLayout()和onMeasure()，可以得到宽高了，当获得正确的宽高后，请移除这个观察者，否则回调会多次执行

//获得ViewTreeObserver 
ViewTreeObserver observer=view.getViewTreeObserver();
//注册观察者，监听变化
observer.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
       @Override
       public boolean onPreDraw() {
          if(observer.isAlive()){
            observer.removeOnDrawListener(this);
             }
          //获得宽高
           int viewWidth=view.getMeasuredWidth();
           int viewHeight=view.getMeasuredHeight();
           return true;
     }
   });

源码

interface KeyboardHeightObserver


public interface KeyboardHeightObserver {
    /**
     * Called when the keyboard height has changed, 0 means keyboard is closed,
     * >= 1 means keyboard is opened.
     *
     * @param height        The height of the keyboard in pixels
     * @param orientation   The orientation either: Configuration.ORIENTATION_PORTRAIT or
     *                      Configuration.ORIENTATION_LANDSCAPE
     */
    void onKeyboardHeightChanged(int height, int orientation);
}

class KeyboardHeightProvider


import android.app.Activity;
import android.content.res.Configuration;
import android.graphics.Point;
import android.graphics.Rect;
import android.graphics.drawable.ColorDrawable;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewTreeObserver;
import android.view.WindowManager;
import android.widget.PopupWindow;

/**
 * The keyboard height provider, this class uses a PopupWindow
 * to calculate the window height when the floating keyboard is opened and closed.
 */
public class KeyboardHeightProvider extends PopupWindow {

    /** The tag for logging purposes */
    private final static String TAG = "sample_KeyboardHeightProvider";

    /** The keyboard height observer */
    private KeyboardHeightObserver observer;

    /** The cached landscape height of the keyboard */
    private int keyboardLandscapeHeight;

    /** The cached portrait height of the keyboard */
    private int keyboardPortraitHeight;

    /** The view that is used to calculate the keyboard height */
    private View popupView;

    /** The parent view */
    private View parentView;

    /** The root activity that uses this KeyboardHeightProvider */
    private Activity activity;

    /**
     * Construct a new KeyboardHeightProvider
     *
     * @param activity The parent activity
     * @param layoutId   R.layout.*
     */
    public KeyboardHeightProvider(Activity activity, int layoutId) {
        super(activity);
        this.activity = activity;

        LayoutInflater inflator = (LayoutInflater) activity.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        this.popupView = inflator.inflate(layoutId, null, false);
        setContentView(popupView);

        setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_RESIZE | WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_VISIBLE);
        setInputMethodMode(PopupWindow.INPUT_METHOD_NEEDED);

        parentView = activity.findViewById(android.R.id.content);

        setWidth(0);
        setHeight(WindowManager.LayoutParams.MATCH_PARENT);

        popupView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                if (popupView != null) {
                    handleOnGlobalLayout();
                }
            }
        });
    }

    /**
     * Start the KeyboardHeightProvider, this must be called after the onResume of the Activity.
     * PopupWindows are not allowed to be registered before the onResume has finished
     * of the Activity.
     */
    public void start() {

        if (!isShowing() && parentView.getWindowToken() != null) {
            setBackgroundDrawable(new ColorDrawable(0));
            showAtLocation(parentView, Gravity.NO_GRAVITY, 0, 0);
        }
    }

    /**
     * Close the keyboard height provider,
     * this provider will not be used anymore.
     */
    public void close() {
        this.observer = null;
        dismiss();
    }

    /**
     * Set the keyboard height observer to this provider. The
     * observer will be notified when the keyboard height has changed.
     * For example when the keyboard is opened or closed.
     *
     * @param observer The observer to be added to this provider.
     */
    public void setKeyboardHeightObserver(KeyboardHeightObserver observer) {
        this.observer = observer;
    }

    /**
     * Get the screen orientation
     *
     * @return the screen orientation
     */
    private int getScreenOrientation() {
        return activity.getResources().getConfiguration().orientation;
    }

    /**
     * Popup window itself is as big as the window of the Activity.
     * The keyboard can then be calculated by extracting the popup view bottom
     * from the activity window height.
     */
    private void handleOnGlobalLayout() {

        Point screenSize = new Point();
        activity.getWindowManager().getDefaultDisplay().getSize(screenSize);

        Rect rect = new Rect();
        popupView.getWindowVisibleDisplayFrame(rect);

        // REMIND, you may like to change this using the fullscreen size of the phone
        // and also using the status bar and navigation bar heights of the phone to calculate
        // the keyboard height. But this worked fine on a Nexus.
        int orientation = getScreenOrientation();
        int keyboardHeight = screenSize.y - rect.bottom;

        if (keyboardHeight == 0) {
            notifyKeyboardHeightChanged(0, orientation);
        }
        else if (orientation == Configuration.ORIENTATION_PORTRAIT) {
            this.keyboardPortraitHeight = keyboardHeight;
            notifyKeyboardHeightChanged(keyboardPortraitHeight, orientation);
        }
        else {
            this.keyboardLandscapeHeight = keyboardHeight;
            notifyKeyboardHeightChanged(keyboardLandscapeHeight, orientation);
        }
    }

    private void notifyKeyboardHeightChanged(int height, int orientation) {
        if (observer != null) {
            observer.onKeyboardHeightChanged(height, orientation);
        }
    }
}

转载于:https://www.cnblogs.com/asche/p/10104459.html