关于Android系统栏中back和home键的实现

分类：Android, Java 阅读 (2,705)

8月 252020

转载请注明原文地址：http://bcoder.com/java/implemention-of-back-button-and-home-button-in-android-system-ui-bar

本文基于Android8.1系统编写

一、背景

　　今天想实现自定义的back和home键，比着葫芦画瓢，把back和home键的部局抄过来了。但怎么也没找到back和home键的java功能实现部分。

后来度娘了一下才找到实现的原理。

　　参考链接：http://blog.chinaunix.net/uid-701715-id-3054850.html

　　自己也记录一下

二、按钮的组件类KeyButtonView

　　在部局中可以看到，back和home键用了一个自定义view，开始我还以为是为了实现按钮的动画效果才自定义了一个这个view，现在发现自己天真了！

　　KeyButtonView的核心在于，他定义了一个可设置的部局属性keyCode，用于设置按钮对应的键，如下back键的部局代码：

<com.android.systemui.statusbar.policy.KeyButtonView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:systemui="http://schemas.android.com/apk/res-auto"
    android:id="@+id/back"
    android:layout_width="@dimen/navigation_key_width"
    android:layout_height="match_parent"
    android:layout_weight="0"
    systemui:keyCode="4"
    android:scaleType="fitCenter"
    android:contentDescription="@string/accessibility_back"
    android:paddingTop="15dp"
    android:paddingBottom="15dp"
    android:paddingStart="@dimen/navigation_key_padding"
    android:paddingEnd="@dimen/navigation_key_padding"

<com.android.systemui.statusbar.policy.KeyButtonView

xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:systemui="http://schemas.android.com/apk/res-auto"

android:id="@+id/back"

android:layout_width="@dimen/navigation_key_width"

android:layout_height="match_parent"

android:layout_weight="0"

systemui:keyCode="4"

android:scaleType="fitCenter"

android:contentDescription="@string/accessibility_back"

android:paddingTop="15dp"

android:paddingBottom="15dp"

android:paddingStart="@dimen/navigation_key_padding"

android:paddingEnd="@dimen/navigation_key_padding"

　　keyCode=”4″对应的为KeyEvent.KEYCODE_BACK键

　　在KeyButtonView的构造函数中，读取并保存了这个属性：

    public KeyButtonView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs);

        //...省略前面的代码
        mCode = a.getInteger(R.styleable.KeyButtonView_keyCode, 0);
　　//...省略后面的代码
    }

public KeyButtonView(Context context, AttributeSet attrs, int defStyle) {

super(context, attrs);

//...省略前面的代码

mCode = a.getInteger(R.styleable.KeyButtonView_keyCode, 0);

　　//...省略后面的代码

}

　　如此，在部局文件中设置的keyCode读到了类中

三、模拟发送按键

　　原理是，拦截onTouch事件，当按钮按下时发送keyCode的ACTION_DOWN操作，当按钮弹开时发送keyCode的ACTION_UP操作，完成一次按键的操作。

    public boolean onTouchEvent(MotionEvent ev) {
　　//...省略部分代码

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mDownTime = SystemClock.uptimeMillis();
                mLongClicked = false;
                setPressed(true);
                if (mCode != 0) {
                    sendEvent(KeyEvent.ACTION_DOWN, 0, mDownTime);
                } else {
                    // Provide the same haptic feedback that the system offers for virtual keys.
                    performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY);
                }
                playSoundEffect(SoundEffectConstants.CLICK);
                removeCallbacks(mCheckLongPress);
                postDelayed(mCheckLongPress, ViewConfiguration.getLongPressTimeout());
                break;
            case MotionEvent.ACTION_MOVE:
                //...省略
            case MotionEvent.ACTION_CANCEL:
　　　　//...省略
                break;
            case MotionEvent.ACTION_UP:
                final boolean doIt = isPressed() && !mLongClicked;
                setPressed(false);
                // Always send a release ourselves because it doesn't seem to be sent elsewhere
                // and it feels weird to sometimes get a release haptic and other times not.
                if ((SystemClock.uptimeMillis() - mDownTime) > 150 && !mLongClicked) {
                    performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY_RELEASE);
                }
                if (mCode != 0) {
                    if (doIt) {
                        sendEvent(KeyEvent.ACTION_UP, 0);
                        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
                    } else {
                        sendEvent(KeyEvent.ACTION_UP, KeyEvent.FLAG_CANCELED);
                    }
                } else {
                    // no key code, just a regular ImageView
                    if (doIt && mOnClickListener != null) {
                        mOnClickListener.onClick(this);
                        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
                    }
                }
                removeCallbacks(mCheckLongPress);
                break;
        }

        return true;
    }

public boolean onTouchEvent(MotionEvent ev) {

　　//...省略部分代码

switch (action) {

case MotionEvent.ACTION_DOWN:

mDownTime = SystemClock.uptimeMillis();

mLongClicked = false;

setPressed(true);

if (mCode != 0) {

sendEvent(KeyEvent.ACTION_DOWN, 0, mDownTime);

} else {

// Provide the same haptic feedback that the system offers for virtual keys.

performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY);

}

playSoundEffect(SoundEffectConstants.CLICK);

removeCallbacks(mCheckLongPress);

postDelayed(mCheckLongPress, ViewConfiguration.getLongPressTimeout());

break;

case MotionEvent.ACTION_MOVE:

//...省略

case MotionEvent.ACTION_CANCEL:

　　　　//...省略

break;

case MotionEvent.ACTION_UP:

final boolean doIt = isPressed() && !mLongClicked;

setPressed(false);

// Always send a release ourselves because it doesn't seem to be sent elsewhere

// and it feels weird to sometimes get a release haptic and other times not.

if ((SystemClock.uptimeMillis() - mDownTime) > 150 && !mLongClicked) {

performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY_RELEASE);

}

if (mCode != 0) {

if (doIt) {

sendEvent(KeyEvent.ACTION_UP, 0);

sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

} else {

sendEvent(KeyEvent.ACTION_UP, KeyEvent.FLAG_CANCELED);

}

} else {

// no key code, just a regular ImageView

if (doIt && mOnClickListener != null) {

mOnClickListener.onClick(this);

sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);

}

removeCallbacks(mCheckLongPress);

break;

}

return true;

}

　　sendEvent函数，先构造KeyEvent对象，然后通过InputManager发送到系统，代码如下：

    void sendEvent(int action, int flags, long when) {
        //...省略部分代码
        final int repeatCount = (flags & KeyEvent.FLAG_LONG_PRESS) != 0 ? 1 : 0;
        final KeyEvent ev = new KeyEvent(mDownTime, when, action, mCode, repeatCount,
                0, KeyCharacterMap.VIRTUAL_KEYBOARD, 0,
                flags | KeyEvent.FLAG_FROM_SYSTEM | KeyEvent.FLAG_VIRTUAL_HARD_KEY,
                InputDevice.SOURCE_KEYBOARD);
        InputManager.getInstance().injectInputEvent(ev,
                InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);
    }

void sendEvent(int action, int flags, long when) {

//...省略部分代码

final int repeatCount = (flags & KeyEvent.FLAG_LONG_PRESS) != 0 ? 1 : 0;

final KeyEvent ev = new KeyEvent(mDownTime, when, action, mCode, repeatCount,

0, KeyCharacterMap.VIRTUAL_KEYBOARD, 0,

flags | KeyEvent.FLAG_FROM_SYSTEM | KeyEvent.FLAG_VIRTUAL_HARD_KEY,

InputDevice.SOURCE_KEYBOARD);

InputManager.getInstance().injectInputEvent(ev,

InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);

}

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