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：
1 public static final int KEYCODE_UNKNOWN = 0; 2 /** Key code constant: Soft Left key. */ 3 public static final int KEYCODE_SOFT_LEFT = 1; 4 /** Key code constant: Soft Right key. */ 5 public static final int KEYCODE_SOFT_RIGHT = 2; 6 /** Key code constant: Home key. */ 7 public static final int KEYCODE_HOME = 3; 8 /** Key code constant: Back key. */ 9 public static final int KEYCODE_BACK = 4; 10 /** Key code constant: Call key. */ 11 public static final int KEYCODE_CALL = 5; 12 /** Key code constant: End Call key. */ 13 public static final int KEYCODE_ENDCALL = 6; 14 /** Key code constant: '0' key. */ 15 public static final int KEYCODE_0 = 7; 16 /** Key code constant: '1' key. */ 17 public static final int KEYCODE_1 = 8; 18 /** Key code constant: '2' key. */ 19 public static final int KEYCODE_2 = 9; 20 /** Key code constant: '3' key. */ 21 public static final int KEYCODE_3 = 10; 22 /** Key code constant: '4' key. */ 23 public static final int KEYCODE_4 = 11; 24 /** Key code constant: '5' key. */ 25 public static final int KEYCODE_5 = 12; 26 /** Key code constant: '6' key. */ 27 public static final int KEYCODE_6 = 13; 28 /** Key code constant: '7' key. */ 29 public static final int KEYCODE_7 = 14; 30 /** Key code constant: '8' key. */ 31 public static final int KEYCODE_8 = 15; 32 /** Key code constant: '9' key. */ 33 public static final int KEYCODE_9 = 16; 34 /** Key code constant: '*' key. */ 35 public static final int KEYCODE_STAR = 17; 36 /** Key code constant: '#' key. */ 37 public static final int KEYCODE_POUND = 18; 38 /** Key code constant: Directional Pad Up key. 39 * May also be synthesized from trackball motions. */ 40 public static final int KEYCODE_DPAD_UP = 19; 41 /** Key code constant: Directional Pad Down key. 42 * May also be synthesized from trackball motions. */ 43 public static final int KEYCODE_DPAD_DOWN = 20; 44 /** Key code constant: Directional Pad Left key. 45 * May also be synthesized from trackball motions. */ 46 public static final int KEYCODE_DPAD_LEFT = 21; 47 /** Key code constant: Directional Pad Right key. 48 * May also be synthesized from trackball motions. */ 49 public static final int KEYCODE_DPAD_RIGHT = 22; 50 /** Key code constant: Directional Pad Center key. 51 * May also be synthesized from trackball motions. */ 52 public static final int KEYCODE_DPAD_CENTER = 23; 53 /** Key code constant: Volume Up key. 54 * Adjusts the speaker volume up. */ 55 public static final int KEYCODE_VOLUME_UP = 24; 56 /** Key code constant: Volume Down key. 57 * Adjusts the speaker volume down. */ 58 public static final int KEYCODE_VOLUME_DOWN = 25; 59 /** Key code constant: Power key. */ 60 public static final int KEYCODE_POWER = 26; 61 /** Key code constant: Camera key. 62 * Used to launch a camera application or take pictures. */ 63 public static final int KEYCODE_CAMERA = 27; 64 /** Key code constant: Clear key. */ 65 public static final int KEYCODE_CLEAR = 28; 66 /** Key code constant: 'A' key. */ 67 public static final int KEYCODE_A = 29; 68 /** Key code constant: 'B' key. */ 69 public static final int KEYCODE_B = 30; 70 /** Key code constant: 'C' key. */ 71 public static final int KEYCODE_C = 31; 72 /** Key code constant: 'D' key. */ 73 public static final int KEYCODE_D = 32; 74 /** Key code constant: 'E' key. */ 75 public static final int KEYCODE_E = 33; 76 /** Key code constant: 'F' key. */ 77 public static final int KEYCODE_F = 34; 78 /** Key code constant: 'G' key. */ 79 public static final int KEYCODE_G = 35; 80 /** Key code constant: 'H' key. */ 81 public static final int KEYCODE_H = 36; 82 /** Key code constant: 'I' key. */ 83 public static final int KEYCODE_I = 37; 84 /** Key code constant: 'J' key. */ 85 public static final int KEYCODE_J = 38; 86 /** Key code constant: 'K' key. */ 87 public static final int KEYCODE_K = 39; 88 /** Key code constant: 'L' key. */ 89 public static final int KEYCODE_L = 40; 90 /** Key code constant: 'M' key. */ 91 public static final int KEYCODE_M = 41; 92 /** Key code constant: 'N' key. */ 93 public static final int KEYCODE_N = 42; 94 /** Key code constant: 'O' key. */ 95 public static final int KEYCODE_O = 43; 96 /** Key code constant: 'P' key. */ 97 public static final int KEYCODE_P = 44; 98 /** Key code constant: 'Q' key. */ 99 public static final int KEYCODE_Q = 45; 100 /** Key code constant: 'R' key. */ 101 public static final int KEYCODE_R = 46; 102 /** Key code constant: 'S' key. */ 103 public static final int KEYCODE_S = 47; 104 /** Key code constant: 'T' key. */ 105 public static final int KEYCODE_T = 48; 106 /** Key code constant: 'U' key. */ 107 public static final int KEYCODE_U = 49; 108 /** Key code constant: 'V' key. */ 109 public static final int KEYCODE_V = 50; 110 /** Key code constant: 'W' key. */ 111 public static final int KEYCODE_W = 51; 112 /** Key code constant: 'X' key. */ 113 public static final int KEYCODE_X = 52; 114 /** Key code constant: 'Y' key. */ 115 public static final int KEYCODE_Y = 53; 116 /** Key code constant: 'Z' key. */ 117 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：
1 Instrumentation inst = new Instrumentation(); 2 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，
1 Handler handler;
b、之后在onCreate方法中定义线程并启动，
1 Thread t = new Thread() { 2 public void run() { 3 Looper.prepare(); 4 handler = new Handler() { 5 public void handleMessage(Message msg) { 6 Instrumentation inst = new Instrumentation(); 7 //inst.sendCharacterSync(msg.what); 8 inst.sendKeyDownUpSync(msg.what); 9 } 10 }; 11 Looper.loop(); 12 } 13 }; 14 t.start();
注意上述代码中的注释部分，实践证明两种方法（sendCharacterSync(int keycode)，sendKeyDownUpSync(int keycode)）都可以达到预期的效果。
c、线程开启了，就差发送带按键值的消息了，在执行代码块中添加以下代码即可，
1 Message msg = new Message(); 2 //msg.what = KeyEvent.KEYCODE_BACK; 3 String s = key_value.getText().toString(); 4 if(!("".equals(s)) && s.matches("^[0-9]*$")){ 5 msg.what = Integer.parseInt(s); 6 handler.sendMessage(msg); 7 } 8 else{ 9 Toast.makeText(getApplicationContext(),"please input a right keycde",Toast.LENGTH_SHORT).show(); 10 }
这里键值是附带在消息对象的what成员身上的，实现方法很多种，这里不一一给出了。
可以看到，代码中注释部分是将键值固定了：
msg.what = KeyEvent.KEYCODE_BACK;
这样做不管是调试，还是以后运行应用程序来模拟按键，都不太实用，每次都要重新设定并运行程序。
所以，本程序采用后面一种方式：
在主界面上多定义一个编辑框组件key_value，模拟之前输入想要的键值即可（需要将键值由输入的String型转为int型）。
当然，前提是需要对按键与对应的值有个大致的了解，而且，在发送消息之前需要对输入的键值进行空与整型的合法性判断，否则会出现难以察觉的异常。
4、经过测试，发现一些按键是不能通过模拟来达到真实效果的。
如Home键，官方给出的文档显示：Home键不再对一般应用允许模拟，即设置了权限。
和手机全屏截取API类似，需要System级或者Root级应用才可以实现想要的效果。
其所给出的替代方案也行不通：Called to process key events. You can override this to intercept all key events before they are dispatched to the window. Be sure to call this implementation for key events that should be handled normally.
5、下面给出一个比较容易的替代方案，虽然比较山寨，效果还行：
1 @Override 2 public boolean onKeyDown(int keyCode, KeyEvent event) { 3 if(keyCode == KeyEvent.KEYCODE_BACK){ 4 Intent intent = new Intent(Intent.ACTION_MAIN); 5 intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); 6 intent.addCategory(Intent.CATEGORY_HOME); 7 this.startActivity(intent); 8 return true; 9 } 10 return super.onKeyDown(keyCode, event); 11 }
需要注意的是，ACTION和CATEGORY的设置和AndroidManifest.xml文件中一致，
标志位设置为Intent.FLAG_ACTIVITY_NEW_TASK，如果不是，则不是以一个新任务的角色生成，会出现问题。