记得以前在做一个C++项目时，需要在某一步操作之后人为用代码模拟敲键盘上的回车键（Enter）效果。出于好奇，这几天研究了一下Android中手机（或平板）上各种按键的键值、模拟方法及最终效果。
1、先来看看Android中对按键和值的定义方式：
public static final int KEYCODE_UNKNOWN = 0;
/** Key code constant: Soft Left key. */
public static final int KEYCODE_SOFT_LEFT = 1;
/** Key code constant: Soft Right key. */
public static final int KEYCODE_SOFT_RIGHT = 2;
/** Key code constant: Home key. */
public static final int KEYCODE_HOME = 3;
/** Key code constant: Back key. */
public static final int KEYCODE_BACK = 4;
/** Key code constant: Call key. */
public static final int KEYCODE_CALL = 5;
/** Key code constant: End Call key. */
public static final int KEYCODE_ENDCALL = 6;
/** Key code constant: '0' key. */
public static final int KEYCODE_0 = 7;
/** Key code constant: '1' key. */
public static final int KEYCODE_1 = 8;
/** Key code constant: '2' key. */
public static final int KEYCODE_2 = 9;
/** Key code constant: '3' key. */
public static final int KEYCODE_3 = 10;
/** Key code constant: '4' key. */
public static final int KEYCODE_4 = 11;
/** Key code constant: '5' key. */
public static final int KEYCODE_5 = 12;
/** Key code constant: '6' key. */
public static final int KEYCODE_6 = 13;
/** Key code constant: '7' key. */
public static final int KEYCODE_7 = 14;
/** Key code constant: '8' key. */
public static final int KEYCODE_8 = 15;
/** Key code constant: '9' key. */
public static final int KEYCODE_9 = 16;
/** Key code constant: '*' key. */
public static final int KEYCODE_STAR = 17;
/** Key code constant: '#' key. */
public static final int KEYCODE_POUND = 18;
/** Key code constant: Directional Pad Up key.
* May also be synthesized from trackball motions. */
public static final int KEYCODE_DPAD_UP = 19;
/** Key code constant: Directional Pad Down key.
* May also be synthesized from trackball motions. */
public static final int KEYCODE_DPAD_DOWN = 20;
/** Key code constant: Directional Pad Left key.
* May also be synthesized from trackball motions. */
public static final int KEYCODE_DPAD_LEFT = 21;
/** Key code constant: Directional Pad Right key.
* May also be synthesized from trackball motions. */
public static final int KEYCODE_DPAD_RIGHT = 22;
/** Key code constant: Directional Pad Center key.
* May also be synthesized from trackball motions. */
public static final int KEYCODE_DPAD_CENTER = 23;
/** Key code constant: Volume Up key.
* Adjusts the speaker volume up. */
public static final int KEYCODE_VOLUME_UP = 24;
/** Key code constant: Volume Down key.
* Adjusts the speaker volume down. */
public static final int KEYCODE_VOLUME_DOWN = 25;
/** Key code constant: Power key. */
public static final int KEYCODE_POWER = 26;
/** Key code constant: Camera key.
* Used to launch a camera application or take pictures. */
public static final int KEYCODE_CAMERA = 27;
/** Key code constant: Clear key. */
public static final int KEYCODE_CLEAR = 28;
/** Key code constant: 'A' key. */
public static final int KEYCODE_A = 29;
/** Key code constant: 'B' key. */
public static final int KEYCODE_B = 30;
/** Key code constant: 'C' key. */
public static final int KEYCODE_C = 31;
/** Key code constant: 'D' key. */
public static final int KEYCODE_D = 32;
/** Key code constant: 'E' key. */
public static final int KEYCODE_E = 33;
/** Key code constant: 'F' key. */
public static final int KEYCODE_F = 34;
/** Key code constant: 'G' key. */
public static final int KEYCODE_G = 35;
/** Key code constant: 'H' key. */
public static final int KEYCODE_H = 36;
/** Key code constant: 'I' key. */
public static final int KEYCODE_I = 37;
/** Key code constant: 'J' key. */
public static final int KEYCODE_J = 38;
/** Key code constant: 'K' key. */
public static final int KEYCODE_K = 39;
/** Key code constant: 'L' key. */
public static final int KEYCODE_L = 40;
/** Key code constant: 'M' key. */
public static final int KEYCODE_M = 41;
/** Key code constant: 'N' key. */
public static final int KEYCODE_N = 42;
/** Key code constant: 'O' key. */
public static final int KEYCODE_O = 43;
/** Key code constant: 'P' key. */
public static final int KEYCODE_P = 44;
/** Key code constant: 'Q' key. */
public static final int KEYCODE_Q = 45;
/** Key code constant: 'R' key. */
public static final int KEYCODE_R = 46;
/** Key code constant: 'S' key. */
public static final int KEYCODE_S = 47;
/** Key code constant: 'T' key. */
public static final int KEYCODE_T = 48;
/** Key code constant: 'U' key. */
public static final int KEYCODE_U = 49;
/** Key code constant: 'V' key. */
public static final int KEYCODE_V = 50;
/** Key code constant: 'W' key. */
public static final int KEYCODE_W = 51;
/** Key code constant: 'X' key. */
public static final int KEYCODE_X = 52;
/** Key code constant: 'Y' key. */
public static final int KEYCODE_Y = 53;
/** Key code constant: 'Z' key. */
public static final int KEYCODE_Z = 54;
其实，在源文件KeyEvent.java中总共定义了将近260个键值，这里只给出了27个（Back、Home、数字、大写字母等）。
2、而要在程序代码中模拟按键的作用，最好是结合线程一起使用，否则有些按键在模拟过程中会出现程序异常终止的情况。
如返回键Back，键值为4，若是直接模拟，就会运行即终止。代码很简单，只需要两句：
Instrumentation inst = new Instrumentation();
inst.sendCharacterSync(KeyEvent.KEYCODE_BACK);
Instrumentation和Activity有点类似，只不过Activity是需要一个界面的，而Instrumentation并不是这样的。
我们可以将它理解为一种没有图形界面的，具有启动能力的，用于监控其他类(用Target Package声明)的工具类。
3、接下来，老老实实利用线程（Thread）来实现按键的模拟效果，当然还用到了消息机制（Handler、Message）：
a、首先在onCreate()方法之前定义Handler对象handler，
Handler handler;
b、之后在onCreate方法中定义线程并启动，