主要用于研发，写软件，玩的话就没有必要了。
例子：
adb shell input keyevent 4 #这条命令相当于按了设备的Backkey键
adb shell input keyevent 3 #press home key
每个数字与keycode对应表如下：
0 --> "KEYCODE_UNKNOWN"
1 --> "KEYCODE_MENU"2 --> "KEYCODE_SOFT_RIGHT"3 --> "KEYCODE_HOME"4 --> "KEYCODE_BACK"5 --> "KEYCODE_CALL"6 --> "KEYCODE_ENDCALL"7 --> "KEYCODE_0"8 --> "KEYCODE_1"9 --> "KEYCODE_2"10 --> "KEYCODE_3"11 --> "KEYCODE_4"12 --> "KEYCODE_5"13 --> "KEYCODE_6"14 --> "KEYCODE_7"15 --> "KEYCODE_8"16 --> "KEYCODE_9"17 --> "KEYCODE_STAR"18 --> "KEYCODE_POUND"19 --> "KEYCODE_DPAD_UP"20 --> "KEYCODE_DPAD_DOWN"21 --> "KEYCODE_DPAD_LEFT"22 --> "KEYCODE_DPAD_RIGHT"23 --> "KEYCODE_DPAD_CENTER"24 --> "KEYCODE_VOLUME_UP"25 --> "KEYCODE_VOLUME_DOWN"26 --> "KEYCODE_POWER"27 --> "KEYCODE_CAMERA"28 --> "KEYCODE_CLEAR"29 --> "KEYCODE_A"30 --> "KEYCODE_B"31 --> "KEYCODE_C"32 --> "KEYCODE_D"33 --> "KEYCODE_E"34 --> "KEYCODE_F"35 --> "KEYCODE_G"36 --> "KEYCODE_H"37 --> "KEYCODE_I"38 --> "KEYCODE_J"39 --> "KEYCODE_K"40 --> "KEYCODE_L"41 --> "KEYCODE_M"42 --> "KEYCODE_N"43 --> "KEYCODE_O"44 --> "KEYCODE_P"45 --> "KEYCODE_Q"46 --> "KEYCODE_R"47 --> "KEYCODE_S"48 --> "KEYCODE_T"49 --> "KEYCODE_U"50 --> "KEYCODE_V"51 --> "KEYCODE_W"52 --> "KEYCODE_X"53 --> "KEYCODE_Y"54 --> "KEYCODE_Z"55 --> "KEYCODE_COMMA"56 --> "KEYCODE_PERIOD"57 --> "KEYCODE_ALT_LEFT"58 --> "KEYCODE_ALT_RIGHT"59 --> "KEYCODE_SHIFT_LEFT"60 --> "KEYCODE_SHIFT_RIGHT"61 --> "KEYCODE_TAB"62 --> "KEYCODE_SPACE"63 --> "KEYCODE_SYM"64 --> "KEYCODE_EXPLORER"65 --> "KEYCODE_ENVELOPE"66 --> "KEYCODE_ENTER"67 --> "KEYCODE_DEL"68 --> "KEYCODE_GRAVE"69 --> "KEYCODE_MINUS"70 --> "KEYCODE_EQUALS"71 --> "KEYCODE_LEFT_BRACKET"72 --> "KEYCODE_RIGHT_BRACKET"73 --> "KEYCODE_BACKSLASH"74 --> "KEYCODE_SEMICOLON"75 --> "KEYCODE_APOSTROPHE"76 --> "KEYCODE_SLASH"77 --> "KEYCODE_AT"78 --> "KEYCODE_NUM"79 --> "KEYCODE_HEADSETHOOK"80 --> "KEYCODE_FOCUS"81 --> "KEYCODE_PLUS"82 --> "KEYCODE_MENU"83 --> "KEYCODE_NOTIFICATION"84 --> "KEYCODE_SEARCH"85 --> "TAG_LAST_KEYCODE"