Android在线手册

Dialog一般指可以显示在Activity前面的小窗口，当前的Activity失去焦点（Focus），Dialog将接受用户输入，一般可以用来显示消息或接受用户输入等等。使用Dialog时一般不需要直接创建Dialog类的实例。而是可以使用AlertDialog,ProgressDialog,DatePickerDialog,TimePickerDialog。最常用的是AlertDialog。下面就以使用AlertDialog为例，使用AlertDialog来选择显示图像的三个例子：DrawMap, JumbleImage，SeeThroughImage。其中DrawMap暂时不介绍，将在后面介绍Internet应用显示在线地图时再说。

通常Dialog是作为Activity一部分来创建的，也就是说在Activity的onCreateDialog(int)中创建。当在onCreateDialog(int)创建Dialog时，Android系统将自动管理Dialog的状态，并把当前Activity作为Dialog的所有者。并且Dialog也继承当前Activity的一些属性，比如说Option Menu。

创建好Dialog后，可以使用showDialog(int) 来显示Dialog ，showDialog的参数为Dialog的ID。在显示Dialog之前，如果想对Dialog做些改动，可以在 onPrepareDialog(int, Dialog) 添加代码。dismiss()关闭对话框。如果在Activity中则使用dismissDialog(int) 。

本例中使用一个按钮来触发Dialog，在res\layout 在添加images.xml

<?xml version=”1.0″ encoding=”utf-8″?>
<LinearLayout xmlns:android=”Http://schemas.android.com/apk/res/android”
    android:orientation=”vertical”
    android:background=”@drawable/white”
 android:layout_width=”fill_parent”
 android:layout_height=”fill_parent”>
    <com.pstreets.graphics2d.GuidebeeGraphics2DView
     android:id=”@+id/graphics2dview”
     android:layout_weight=”1″
     android:layout_width=”fill_parent”
     android:layout_height=”wrap_content”/>
 <LinearLayout xmlns:android=”http://schemas.android.com/apk/res/android”
  android:layout_width=”wrap_content” android:layout_height=”wrap_content”
  android:orientation=”horizontal”
  
  >
  
   <Button android:text=”Images”
       android:id=”@+id/btnImages”
    android:layout_width=”wrap_content”
    android:textColor=”@color/black”
    android:checked=”true”
    android:layout_height=”wrap_content”>
   </Button>
  
 </LinearLayout>

</LinearLayout>

修改Image.java

public class Images extends Graphics2DActivity
implements OnClickListener{

 private Button btnImages;
 private int[] imageDuke;
 
 static final private int IMAGE_DIALOG=1;
 
 int w, h;
    int offX, offY;
   
 int alpha = 128;
 FontEx font = FontEx.getSystemFont();
    int fontSize = 24;
    Pen pen = new Pen(Color.RED, 2);
    char[] message = "Guidebee".toCharArray();
    int widthOfMessage = 0;
   
   
    private int numlocs = 2;
    private int numcells = numlocs * numlocs;
    private int[] cells;
    int  cw, ch;
 
 
   
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.images);
  graphic2dView = (GuidebeeGraphics2DView)
      findViewById(R.id.graphics2dview);
  btnImages = (Button) findViewById(R.id.btnImages);
  btnImages.setOnClickListener(this);
  Bitmap bitmap
    = BitmapFactory.decodeResource(getResources(),
    R.drawable.duke_skateboard);
  imageDuke = new int[bitmap.getHeight()
                          * bitmap.getWidth()];
  bitmap.getPixels(imageDuke, 0, bitmap.getWidth(), 0, 0,
    bitmap.getWidth(), bitmap.getHeight());
  widthOfMessage = font.charsWidth(message, 0,
    message.length, fontSize);
  w=bitmap.getWidth();
     h=bitmap.getHeight();
        offX = (SharedGraphics2DInstance.CANVAS_WIDTH - w) / 2;
        offY = (SharedGraphics2DInstance.CANVAS_HEIGHT - h) / 2;
      
        cw = w / numlocs;
        ch = h / numlocs;
        cells = new int[numcells];
        for (int i = 0; i < numcells; i++) {
            cells[i] = i;
        }
       

 }
 
 private void drawJumbleImage(){
  RanDOM rand = new Random();
        int ri;
        for (int i = 0; i < numcells; i++) {
            while ((ri = rand.nextInt(numlocs)) == i) {
            }

            int tmp = cells[i];
            cells[i] = cells[ri];
            cells[ri] = tmp;
        }
        graphics2D.clear(Color.WHITE);
        graphics2D.Reset();

        int dx, dy;
        for (int x = 0; x < numlocs; x++) {
            int sx = x * cw;
            for (int y = 0; y < numlocs; y++) {
                int sy = y * ch;
                int cell = cells[x * numlocs + y];
                dx = (cell / numlocs) * cw;
                dy = (cell % numlocs) * ch;
                graphics2D.drawImage(imageDuke, w, h,
                        dx + offX, dy + offY,
                        sx, sy, cw, ch);
            }
        }
       
        graphic2dView.refreshCanvas();
 }
 
 private void drawSeeThroughImage(){
  alpha += 16;
  if(alpha>255) alpha=0;
  graphics2D.clear(Color.WHITE);
  graphics2D.Reset();
  graphics2D.setDefaultPen(pen);
        graphics2D.drawChars(font, fontSize, message,
          0, message.length, offX
                + (w - widthOfMessage) / 2, offY + h / 2);
        graphics2D.drawImage(imageDuke, w, h,
                offX, offY,
                0xFFFF00FF, alpha);
        graphic2dView.refreshCanvas();
 }
 
 protected Dialog onCreateDialog(int id) {   
  Dialog dialog;   
  switch(id) {   
     case IMAGE_DIALOG:     
      final CharSequence[] items = {"DrawMap",
        "JumbleImage","SeeThroughImage"};
      AlertDialog.Builder builder
      = new AlertDialog.Builder(this);
      builder.setTitle("Images");
      builder.setSingleChoiceItems(items,
        -1, new DialogInterface.OnClickListener() {   
            public void onClick(DialogInterface dialog,
              int item) {       
               switch(item){
               case 0:
              
                break;
               case 1:
                drawJumbleImage();
                break;
               case 2:
                drawSeeThroughImage();
                break;

               }
               dialog.dismiss();
           }
           });
           AlertDialog alert = builder.create();
         dialog=alert;
         break;       
           default:       
            dialog = null;  
         } 
     return dialog;
  }
  
 @Override
 protected void drawImage() {
  drawJumbleImage();
  
 }

 @Override
 public void onClick(View view) {
  showDialog(IMAGE_DIALOG);
  
 }

}

从代码中看到，Dialog是通过AlertDialog.Builder 来创建的，这里Dialog显示了三个选项，通过builder.setSingleChoiceItems添加处理事件。实际AlertDialog可以有多种选项，具体请参考Android AlertDialog 文档。