一、什么是Android Keycode
Android Keycode(按键代码)是一种描述在安卓设备上触摸屏幕或按下物理按键的操作。在 Android 中, KeyEvent 就是用来描述按键操作的类。KeyEvent 类会保存一个按键动作(如:ACTION_DOWN, ACTION_MULTIPLE, ACTION_UP)和按键码(键值)。
Android定义了一个整型变量叫作KeyCode。按下每个不同的键都会产生不同的KeyCode,KeyCode可以用于定义哪些按键是用于OSD控制按钮、哪些按键是用于输入文本或者控制系统的快捷键。
二、常用的Android Keycode
1. 常用字母数字键
/** * 0键 - 9键 (数字键盘) */ public static final int KEYCODE_0 = 7; public static final int KEYCODE_1 = 8; public static final int KEYCODE_2 = 9; public static final int KEYCODE_3 = 10; public static final int KEYCODE_4 = 11; public static final int KEYCODE_5 = 12; public static final int KEYCODE_6 = 13; public static final int KEYCODE_7 = 14; public static final int KEYCODE_8 = 15; public static final int KEYCODE_9 = 16; /** * A键 - Z键 (字母键盘) */ public static final int KEYCODE_A = 29; public static final int KEYCODE_B = 30; public static final int KEYCODE_C = 31; public static final int KEYCODE_D = 32; public static final int KEYCODE_E = 33; public static final int KEYCODE_F = 34; public static final int KEYCODE_G = 35; public static final int KEYCODE_H = 36; public static final int KEYCODE_I = 37; public static final int KEYCODE_J = 38; public static final int KEYCODE_K = 39; public static final int KEYCODE_L = 40; public static final int KEYCODE_M = 41; public static final int KEYCODE_N = 42; public static final int KEYCODE_O = 43; public static final int KEYCODE_P = 44; public static final int KEYCODE_Q = 45; public static final int KEYCODE_R = 46; public static final int KEYCODE_S = 47; public static final int KEYCODE_T = 48; public static final int KEYCODE_U = 49; public static final int KEYCODE_V = 50; public static final int KEYCODE_W = 51; public static final int KEYCODE_X = 52; public static final int KEYCODE_Y = 53; public static final int KEYCODE_Z = 54;
2. 功能键
功能键位于键盘的左下角,主要控制输入的操作,比如回车、删除等。
public static final int KEYCODE_ENTER = 66; //回车 public static final int KEYCODE_DEL = 67; //删除 public static final int KEYCODE_TAB = 61; //Tab /** * 方向键 */ public static final int KEYCODE_DPAD_UP = 19; // 上箭头 public static final int KEYCODE_DPAD_DOWN = 20; // 下箭头 public static final int KEYCODE_DPAD_LEFT = 21; // 左箭头 public static final int KEYCODE_DPAD_RIGHT = 22; // 右箭头
3. 控制键
如Home按钮、Menu按钮、返回按钮、音量键、亮度键等控制设备的按键。
/** * 控制键 */ public static final int KEYCODE_BACK = 4; //返回键(左下角) public static final int KEYCODE_HOME = 3; //Home键(中间大圆钮) public static final int KEYCODE_APP_SWITCH = 187; //任务键(最近打开的应用列表键) public static final int KEYCODE_VOLUME_UP = 24; //音量增加 public static final int KEYCODE_VOLUME_DOWN = 25; //音量减少 public static final int KEYCODE_BRIGHTNESS_UP = 220;//增加亮度 public static final int KEYCODE_BRIGHTNESS_DOWN = 221;//降低亮度
三、Android Keycode的使用场景
1. 监听键盘事件
我们可以使用 setOnKeyListener()
监听按键事件。
EditText editText = findViewById(R.id.et_input); editText.setOnKeyListener(new View.OnKeyListener() { @Override public boolean onKey(View v, int keyCode, KeyEvent event) { switch (keyCode) { case KeyEvent.KEYCODE_ENTER: //执行回车操作 break; case KeyEvent.KEYCODE_DEL: //执行删除操作 break; } return false; } });
2. 控制音量和亮度
我们可以使用 Keycode 配合AudioManager
和Settings.System
控制音量和亮度。比如,下面这个例子显示了如何控制音量。
AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE); audioManager.adjustStreamVolume(AudioManager.STREAM_MUSIC, AudioManager.ADJUST_LOWER, AudioManager.FLAG_PLAY_SOUND);
下面这个例子展示了如何使用Keycode和API改变屏幕亮度。
int oldBrightness = Settings.System.getInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, 125); int newBrightness = oldBrightness + 10; if (newBrightness > 255) { newBrightness = 255; } else if (newBrightness < 0) { newBrightness = 0; } Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, newBrightness); WindowManager.LayoutParams layoutParams = getWindow().getAttributes(); layoutParams.screenBrightness = newBrightness / 255.0f; getWindow().setAttributes(layoutParams);
3. 控制按键绑定
我们还可以绑定按键到系统事件。例如,我们可以设置KEYCODE_VOLUME_UP
按键控制音量增加。
public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_VOLUME_UP) { // 增加音量 return true; } return super.onKeyDown(keyCode, event); }
四、总结
在 Android 开发中,Keycode 功能强大。可以用来控制设备的按键事件、调节音量和亮度、绑定按键到系统事件等。掌握 Keycode 的基本用法,可以帮助我们更好地开发出满足用户需求的应用。