Android開發 - 獲取系統輸入法高度的正確姿勢

問題與解決

在Android應用的開發中，有一些需求需要我們獲取到輸入法的高度，但是官方的API并沒有提供類似的方法，所以我們需要自己來實現。

查閱了網上很多資料，試過以后都不理想。

比如有的方法通過監聽布局的變化來計算輸入法的高度，這種方式在Activity的配置中配置為"android:windowSoftInputMode="adjustResize""時沒有問題，可以正確獲取輸入法的高度，因為布局此時確實會動態的調整。

但是當Activity配置為"android:windowSoftInputMode="adjustNothing""時，布局不會在輸入法彈出時進行調整，上面的方式就會撲街。

不過經過一番探索和測試，終于發現了一種方式可以在即使設置為adjustNothing時也可以正確計算高度放方法。

同時也感謝這位外國朋友：
GitHub地址

其實也就兩個類，我也做了一些修改，解決了一些問題，這里也貼出來：

• KeyboardHeightObserver.java

/**
 * The observer that will be notified when the height of 
 * the keyboard has changed
 */
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);
}

• KeyboardHeightProvider.java

/**
 * 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
     */
    public KeyboardHeightProvider(Activity activity) {
        super(activity);
        this.activity = activity;

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

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

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

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

        popupView.getViewTreeObserver().addOnGlobalLayoutListener(new 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);
        }
    }
}

使用方法

此處以在Activity中的使用進行舉例。

實現接口

引入這兩個類后，在當前Activity中實現接口KeyboardHeightObserver：

@Override
public void onKeyboardHeightChanged(int height, int orientation) {
    String or = orientation == Configuration.ORIENTATION_PORTRAIT ? "portrait" : "landscape";
    Logger.d(TAG, "onKeyboardHeightChanged in pixels: " + height + " " + or);
}

定義并初始化

在當前Activity定義成員變量，并在onCreate()中進行初始化

private KeyboardHeightProvider mKeyboardHeightProvider;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    ...
    mKeyboardHeightProvider = new KeyboardHeightProvider(this);
    new Handler().post(() -> mKeyboardHeightProvider.start());
}

生命周期處理

初始化完成后，我們要在Activity中的生命周期中也要進行處理，以免內存泄露。

@Override
protected void onResume() {
    super.onResume();
    mKeyboardHeightProvider.setKeyboardHeightObserver(this);
}

@Override
protected void onPause() {
    super.onPause();
    mKeyboardHeightProvider.setKeyboardHeightObserver(null);
}

@Override
protected void onDestroy() {
    super.onDestroy();
    mKeyboardHeightProvider.close();
}

總結

此時我們就可以正確獲取的當前輸入法的高度了，即使android:windowSoftInputMode="adjustNothing"時也可以正確獲取到，這正是這個方法的強大之處，利用這個方法可以實現比如類似微信聊天的界面，流暢切換輸入框，表情框等。

如有更多疑問，請參考我的其它Android相關博客：我的博客地址