當要進行耗時的操作的時候，往往會看見“請稍候”字樣的對話框。例如，用戶正在登入服務器，此時並不允許用戶使用這個軟件，或者應用程序把結果返回給用戶之前，要進行某些耗時的計算。在這些情況下，顯示一個“進度條”對話框，能友好地讓用戶等待，同時也能阻止用戶進行某些不必要的操作。
1.創建一個名為Dialog的工程。
2.main.xml中的代碼。
[java] <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<Button
android:id="@+id/btn_dialog2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="onClick2"
android:text="Click to display a progress dialog" />
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<Button
android:id="@+id/btn_dialog2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="onClick2"
android:text="Click to display a progress dialog" />
</LinearLayout> 3.DialogActivity.java中的代碼。
[java] package net.horsttnann.Dialog;
import net.horsttnann.Dialog.R;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.view.View;
public class DialogActivity extends Activity {
ProgressDialog progressDialog;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void onClick2(View v) {
// —show the dialog—
final ProgressDialog dialog = ProgressDialog.show(this,
"Doing something", "Please wait…", true);
new Thread(new Runnable() {
public void run() {
try {
// —simulate doing something lengthy—
Thread.sleep(5000);
// —dismiss the dialog—
dialog.dismiss();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
}
}
package net.horsttnann.Dialog;
import net.horsttnann.Dialog.R;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.view.View;
public class DialogActivity extends Activity {
ProgressDialog progressDialog;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void onClick2(View v) {
// —show the dialog—
final ProgressDialog dialog = ProgressDialog.show(this,
"Doing something", "Please wait…", true);
new Thread(new Runnable() {
public void run() {
try {
// —simulate doing something lengthy—
Thread.sleep(5000);
// —dismiss the dialog—
dialog.dismiss();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
}
}
4.按F11調試，點擊按鈕，彈出“進度條”對話框。
效果圖：
提示：
基本上，想要創建一個“進度條”對話框，隻需要創建一個ProgressDialog類的實例，然後調用show()方法：
[java] // —show the dialog—
final ProgressDialog dialog = ProgressDialog.show(this,
"Doing something", "Please wait…", true);
// —show the dialog—
final ProgressDialog dialog = ProgressDialog.show(this,
"Doing something", "Please wait…", true); 因為它是一個“模態”的對話框，所以它就會把其他UI組件給遮蓋住，直到它被解除。如果想要在後臺執行一個“長期運行”的任務，可以創建一個線程。run()方法裡面的代碼將會在一個獨立的線程裡面執行。下面的代碼使用sleep()方法，模擬瞭一個需要5秒執行的後臺任務：
[java] new Thread(new Runnable() {
public void run() {
try {
// —simulate doing something lengthy—
Thread.sleep(5000);
// —dismiss the dialog—
dialog.dismiss();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
// —simulate doing something lengthy—
Thread.sleep(5000);
// —dismiss the dialog—
dialog.dismiss();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start(); 5秒鐘之後，執行dismiss()方法，對話框就被解除瞭。
摘自 horsttnann的專欄
