android之DPAD上下左右四个键控制

我们代码的目的很简单，那就是监听上下左右中这几个键的事件触发。直接上代码：

dpad.xml

<?xml version="1.0" encoding="utf-8"?><AbsoluteLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="#FFFFFF" > <Button android:id="@+id/myButton1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="move me" android:layout_x="20px" android:layout_y="40px" /></AbsoluteLayout>

activity代码：

package cn.com.chenzheng_java;import android.app.Activity;import android.os.Bundle;import android.util.DisplayMetrics;import android.view.KeyEvent;import android.widget.AbsoluteLayout;import android.widget.Button;import android.widget.Toast;/** * @description 控制手机的上下左右四个方向键 * @author chenzheng_java * */public class DpadActivity extends Activity {Button button;DisplayMetrics metrics = new DisplayMetrics();int screenx = 0 ;//屏幕宽度int screeny = 0 ;//屏幕高度int buttonWidth = 80;//按钮宽度int buttonHeight = 40 ;// 按钮高度int currentX = 0;// 按钮的当前x坐标int currentY = 0;// 按钮的当前Y坐标int step = 0;//移动时候的步长@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.dpad);button = (Button) findViewById(R.id.myButton1);getWindowManager().getDefaultDisplay().getMetrics(metrics);screenx = metrics.widthPixels;screeny = metrics.heightPixels;/*buttonWidth = button.getWidth();buttonHeight = button.getHeight();*/currentX = (screenx-buttonWidth)/2;currentY = (screeny-buttonHeight)/2;step = 2;button.setLayoutParams(new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, currentX, currentY));}/** * 当前后左右键被按下的时候，被触发(这里可是有前提的哦，那就是当前的activity中必须没有view正在监听按键 * ，例如：当前如果有一个EditText正在等待输入，当我们按下dpad时，不会触发事件哦) * Activity.onKeyDown(); 当某个键被按下时会触发，但不会被任何的该Activity内的任何view处理。 默认按下KEYCODE_BACK键后会回到上一个Activity。 */@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {switch (keyCode) {case KeyEvent.KEYCODE_DPAD_DOWN://按向下键moveDown();break;case KeyEvent.KEYCODE_DPAD_UP:// 按向上键moveUp();case KeyEvent.KEYCODE_DPAD_LEFT://按向左键moveLeft();case KeyEvent.KEYCODE_DPAD_RIGHT://按向右键moveRight();default:break;}return super.onKeyDown(keyCode, event);}@SuppressWarnings("deprecation")private void moveDown(){int temp = currentY+step;if(temp>(screeny-buttonHeight)){showToast("到头了哦！");button.setLayoutParams(new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, screenx, screeny-buttonHeight));}else{currentY = currentY+step;AbsoluteLayout.LayoutParams params = new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, currentX, currentY);button.setLayoutParams(params);}//button.setLayoutParams(new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, currentX, currentY-2));}@SuppressWarnings("deprecation")private void moveUp(){int temp = currentY-step;if(temp<=0){showToast("往上到头了哦！");button.setLayoutParams(new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, screenx, 0));}else{currentY = currentY-step;AbsoluteLayout.LayoutParams params = new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, currentX, currentY);button.setLayoutParams(params);}}@SuppressWarnings("deprecation")private void moveLeft(){int temp = currentX-step;if(temp<=0){showToast("往左边到头了哦！");button.setLayoutParams(new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, 0, screeny));}else{currentX = currentX-step;AbsoluteLayout.LayoutParams params = new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, currentX, currentY);button.setLayoutParams(params);}}@SuppressWarnings("deprecation")private void moveRight(){int temp = currentX+step;if(temp>=(screenx-buttonWidth)){showToast("往右边到头了哦！");button.setLayoutParams(new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, screenx-buttonWidth, currentY));}else{currentX = currentX+step;AbsoluteLayout.LayoutParams params = new AbsoluteLayout.LayoutParams(buttonWidth, buttonHeight, currentX, currentY);button.setLayoutParams(params);}}/** * 弹出提示信息 * @param text 提示信息 */private void showToast(String text){Toast.makeText(this, text, Toast.LENGTH_LONG).show();}}

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       这里我们可以看到，要想监听这几个方向键，那么我们必须重写 public boolean onKeyDown(int keyCode, KeyEvent event)这个方法，该方法定义在Activity中，其中keyCode便是代表着你点击的那个键的标识符，KeyEvent 则是一个事件。

      需要注意的是，坐标问题：我们控制的按钮的坐标实际上是左上角的坐标。而屏幕的向左是X轴，向下是Y轴，也就是说，只要在屏幕内显示的组件，其坐标都是正数的。

     当然键盘中所有的键都可以监听的，我们亦可以来监听A-Z这些键，他们的keyCode依次是KEYCODE_A -------KEYCODE_Z.

     这里有一个小技巧，可以判断出用户输入的是什么A-Z那个字符，代码如下：

int code = 'A'+keycode-29;char ch = (char)code;

如果我们无法获取当前的按键，我们可以通过keycode_unknown来捕捉。

控制音量大小：keycode_volume_down / keycode_volume_up.

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关于KeyEvent，它代表了我们点击键盘时的事件，看下图，我们可以创建自己的键盘事件

其中参数中的action，代表了用户的操作，值为ACTION_DOWN、ACTION_UP、ACTION_MULTIPLE其中的一个。而code则代表了我们的标识符，入上面提到的keycode_volume_down 就是一个code。