今天早上幫朋友調試代碼,說是退出應用代碼無效,仔細看了代碼,寫法上的確沒什麼問題,於是研究了一下,原因如下:
先看兩種情況:
(1)public class MainActivity extends TabActivity implements OnCheckedChangeListener
(2)public class MainActivity extends Activity
都是要在MainActivity下退出整個應用,第一種情況主Activity繼承自TabActivity,第二種情況主Activity繼承自Activity,這是兩者最大的不同,也就是這點差異,能把有效的退出應用代碼變的無效。
雖然TabActivity是Activity的間接子類,但是在TabActivity中,OnKeyDown()事件無法獲取焦點,因爲焦點都在子activity裏面,本人親自做了驗證,在(1)情況下,在onKeyDown()處打斷點無效,無法進行DeBug調試,但在(2)情況下,可以進入DeBug中。下面是退出引用程序的代碼
(1)情況下適用代碼:
@Override
public boolean dispatchKeyEvent(KeyEvent event)
{
// TODO Auto-generated method stub
if (event.getAction() == KeyEvent.ACTION_DOWN &&
event.getKeyCode() == KeyEvent.KEYCODE_BACK)
{
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("您確定要退出應用?").setTitle("提醒")
.setNegativeButton("取消", new DialogInterface.OnClickListener()
{
@Override
public void onClick(DialogInterface arg0, int arg1)
{
arg0.cancel();
}
}).setPositiveButton("確定", new DialogInterface.OnClickListener()
{
public void onClick(DialogInterface dialog, int id)
{
finish();
}
});
AlertDialog alert = builder.create();
alert.show();
return false;
}
return super.dispatchKeyEvent(event);
}
(2)情況下適用代碼一:
@Override
public boolean onKeyDown(int keyCode, KeyEvent event)
{
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0)
{
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("提醒");
builder.setMessage("確認退出應用?");
builder.setPositiveButton("確定", new OnClickListener()
{
@Override
public void onClick(DialogInterface arg0, int arg1)
{
intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
android.os.Process.killProcess(android.os.Process.myPid());
}
});
builder.setNegativeButton("取消", new OnClickListener()
{
@Override
public void onClick(DialogInterface arg0, int arg1)
{
}
});
builder.show();
return true;
}
return super.onKeyDown(keyCode, event);
}
(2)情況下適用代碼二:
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("提示ʾ");
builder.setMessage("確定要退出應用");
builder.setPositiveButton("確定", new OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
finish();
// System.exit(code);
}
});
builder.setNegativeButton("取消", new OnClickListener() {
@Override
public void onClick(DialogInterface arg0, int arg1) {
// TODO Auto-generated method stub
}
});
builder.show();
return true;
}
return super.onKeyDown(keyCode, event);
}
總之一句話,如果繼承的是Activity,就通過OnKeyDown()方法退出程序,如果繼承的事TabActivity,就通過dispathKeyEvent()方法退出應用。