android意圖給nullpointer異常

Question

package com.org.myOxygen.activities;

import java.util.Stack;

import android.app.Activity;
import android.app.ActivityGroup;
import android.app.LocalActivityManager;
import android.content.Intent;
import android.os.Bundle;
import android.view.Window;

public class ApplicationTabActivityGroup extends ActivityGroup{

private static Stack<String> stack;

 @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (stack == null) stack = new Stack<String>();

    //start default activity
    push("Search Activity", new Intent(this, ApplicaitonActivity.class));

  }

  @Override
  public void finishFromChild(Activity child) {

          pop();
  }

  @Override
  public void onBackPressed() 
  {

          pop();
  }


  public void push(String id, Intent intent) 
  {
    Window window = getLocalActivityManager().startActivity(id, intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP));
    if (window != null) {
      stack.push(id);
      setContentView(window.getDecorView());
    }
  }

  public void pop() 
  {
    if (stack.size() == 1) finish();
    LocalActivityManager manager = getLocalActivityManager();

    manager.destroyActivity(stack.pop(), true);

    if (stack.size() > 0) 
    {
      Intent lastIntent = manager.getActivity(stack.peek()).getIntent();
      Window newWindow = manager.startActivity(stack.peek(), lastIntent);
      setContentView(newWindow.getDecorView());
    }
  }

}

我在網上遇到錯誤

Intent lastIntent = manager.getActivity(stack.peek()).getIntent();

錯誤是NullPointerException 。

那里可能出什么問題了？

編輯-1

  11-26 14:58:57.256: E/AndroidRuntime(557): FATAL EXCEPTION: main
11-26 14:58:57.256: E/AndroidRuntime(557): java.lang.NullPointerException
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.org.myOxygen.activities.SearchTabActivityGroup.pop(SearchTabActivityGroup.java:59)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.org.myOxygen.activities.SearchTabActivityGroup.onBackPressed(SearchTabActivityGroup.java:36)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.app.Activity.onKeyUp(Activity.java:1888)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.KeyEvent.dispatch(KeyEvent.java:1061)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.app.Activity.dispatchKeyEvent(Activity.java:2068)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1643)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.widget.TabHost.dispatchKeyEvent(TabHost.java:275)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:788)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:1667)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1102)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.app.Activity.dispatchKeyEvent(Activity.java:2063)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1643)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2471)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2441)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1735)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.os.Handler.dispatchMessage(Handler.java:99)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.os.Looper.loop(Looper.java:123)
11-26 14:58:57.256: E/AndroidRuntime(557):  at android.app.ActivityThread.main(ActivityThread.java:4627)
11-26 14:58:57.256: E/AndroidRuntime(557):  at java.lang.reflect.Method.invokeNative(Native Method)
11-26 14:58:57.256: E/AndroidRuntime(557):  at java.lang.reflect.Method.invoke(Method.java:521)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
11-26 14:58:57.256: E/AndroidRuntime(557):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
11-26 14:58:57.256: E/AndroidRuntime(557):  at dalvik.system.NativeStart.main(Native Method)

這是堆棧跟蹤！

Answer 1

通過查看您的代碼，我發現了一個可以創建NullPointerException的原因，也就是說，可能是您將具有相同id（String）的方法“ public void push（String id，Intent intent）”用於不同的活動。

它創建空指針異常的原因是，當您使用相同的id（String）調用push方法並且Android內存管理器銷毀了與該名稱關聯的舊活動，並且在您的pop方法期間，它返回了null。

希望此答案有助於解決錯誤。

干杯，維拉傑

Answer 2

Javadoc指出getActivity將返回

關聯的Activity對象；如果id未知或當前未實例化其活動，則返回null

也許您的活動沒有被激活，或者被android破壞了。 然后，您應該考慮啟動它。

問候，斯特凡