望塵軒中一盞茶

場景描述：進入一個界面需要先去網絡加載內容，浮出一個進度框提示正在加載中，這時如果按下back鍵返回，本意是返回上一個界面，而系統默認只是dismiss掉了進度框，需要再按一次back鍵才能返回上一個界面。現在想只按一次back鍵就返回上一個界面，催生了本次實驗。具體實現參考代碼：

首先繼承ProgressDialog類，實現自己的進度框類，這里主要是為了在進度框處于焦點時，捕獲其按鍵事件。具體代碼如下：

public class MyDialog extends ProgressDialog {
    private Activity parentActivity;
    public MyDialog(Context context) {
	super(context);
	parentActivity = (Activity) context;
    }
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
	if(parentActivity != null) {
            return parentActivity.onKeyDown(keyCode, event);
	}
	return super.onKeyDown(keyCode, event);
    }
}

這里在進度框處于焦點狀態按下back鍵時，調用了打開進度框的activity的按鍵監聽事件，將相關處理交給activity進行處理。Activity的實現代碼如下：

public class DialogTestActivity extends Activity {

	private MyDialog pDialog;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        showLoadingDialog();
    }

    private void showLoadingDialog() {
    	pDialog = new MyDialog(this);
    	pDialog.setMessage("正在加載中...");
		pDialog.setCancelable(true);
		pDialog.show();
	}

	private void dismissLoadingDialog() {
		if(pDialog != null && pDialog.isShowing()) {
			pDialog.dismiss();
		}
	}

	@Override
	public boolean onKeyDown(int keyCode, KeyEvent event) {
		finish();
		return super.onKeyDown(keyCode, event);
	}

	@Override
	protected void onDestroy() {
		dismissLoadingDialog();
		super.onDestroy();
	}
}

這里在onKeyDown實現里直接調用了Activity的finish()方法來結束Activity，如果不調用此方法就不能實現想要的效果；并在onDestroy()方法里調用了關掉進度框的操作，這里是非常必要的。雖然不調用程序一樣會正常返回，但是在logcat中會看到這里有問題，具體信息如下：

12-20 15:24:51.315: E/WindowManager(6759): Activity com.jade.dialog.DialogTestActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f493c8 that was originally added here
12-20 15:24:51.315: E/WindowManager(6759): android.view.WindowLeaked: Activity com.jade.dialog.DialogTestActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@44f493c8 that was originally added here
12-20 15:24:51.315: E/WindowManager(6759): 	at android.view.ViewRoot.(ViewRoot.java:247)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.view.Window$LocalWindowManager.addView(Window.java:424)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.Dialog.show(Dialog.java:241)
12-20 15:24:51.315: E/WindowManager(6759): 	at com.jade.dialog.DialogTestActivity.showLoadingDialog(DialogTestActivity.java:23)
12-20 15:24:51.315: E/WindowManager(6759): 	at com.jade.dialog.DialogTestActivity.onCreate(DialogTestActivity.java:15)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.ActivityThread.access$2300(ActivityThread.java:125)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.os.Handler.dispatchMessage(Handler.java:99)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.os.Looper.loop(Looper.java:123)
12-20 15:24:51.315: E/WindowManager(6759): 	at android.app.ActivityThread.main(ActivityThread.java:4627)
12-20 15:24:51.315: E/WindowManager(6759): 	at java.lang.reflect.Method.invokeNative(Native Method)
12-20 15:24:51.315: E/WindowManager(6759): 	at java.lang.reflect.Method.invoke(Method.java:521)
12-20 15:24:51.315: E/WindowManager(6759): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
12-20 15:24:51.315: E/WindowManager(6759): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
12-20 15:24:51.315: E/WindowManager(6759): 	at dalvik.system.NativeStart.main(Native Method)

出現上述問題的原因是在Activity調用finish()方法結束自己的時候，進度框尚未關閉。當然也有另外一種方案，就是修改MyDialog中按鍵處理部分，首先dismiss()自己，然后再調用activity的按鍵事件處理方法。具體代碼如下：

public boolean onKeyDown(int keyCode, KeyEvent event) {
	if(parentActivity != null) {
		dismiss(); //在這里自己關掉自己嘍～
		return parentActivity.onKeyDown(keyCode, event);
	}
	return super.onKeyDown(keyCode, event);
}