android 代码实现back键功能

方案一，简单但响应慢：

    doExec("input keyevent 4");

    public String doExec(String cmd) {
        String s = "/n";
        try {
            Process p = Runtime.getRuntime().exec(cmd);
            BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = null;
            while ((line = in.readLine()) != null) {
                s += line + "/n";
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return cmd;
    }

　　

方案二，响应快：

    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                switch (v.getId()) {
                    case R.id.bottom_nav_back:
                        mDownTime = SystemClock.uptimeMillis();
                        sendEvent(KeyEvent.ACTION_DOWN, 0);
                        break;
                break;
            case MotionEvent.ACTION_UP:
                switch (v.getId()) {
                    case R.id.bottom_nav_back:
                    case R.id.tv_back_dec:
                        sendEvent(KeyEvent.ACTION_UP, 0);
                        break;
                break;
			...
			
    private void sendEvent(int action, int flags) {
        sendEvent(action, flags, SystemClock.uptimeMillis());
    }

    private void sendEvent(int action, int flags, long when) {
        final int repeatCount = (flags & KeyEvent.FLAG_LONG_PRESS) != 0 ? 1 : 0;
        final KeyEvent ev = new KeyEvent(mDownTime, when, action, KeyEvent.KEYCODE_BACK, 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);
    }