Android简明开发教程十七：Dialog 显示图像
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
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
|
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。
