Question

我有一个活动说A，开始时需要额外的东西。问题是，当使用 setDisplayHomeAsUpEnabled（true）; 时，在另一个活动上按下后退按钮时说B 我收到错误。错误显然是由于没有从B发送额外内容。当使用 setDisplayHomeAsUpEnabled（true）;

时，如何使用后退按钮将附加内容从B发送到A.

活动A从主要活动

开始

protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_subscreen);
     Bundle extras = getIntent().getExtras();

    titleTask = extras.getString(DatabaseHelper.COLUMN_TITLE);
    titleid = extras.getLong(DatabaseHelper.COLUMN_ROWID);
    actionBar = getSupportActionBar();
    actionBar.setTitle(titleTask);
    actionBar.setDisplayHomeAsUpEnabled(true);
}

从B

按下后退按钮时，记录错误如下

04-26 12:39:54.355: E/AndroidRuntime(15573): java.lang.RuntimeException: Unable to start activity 

ComponentInfo{com.group.RedPanda.FinalProject/com.group.RedPanda.FinalProject.SubScreen}: java.lang.NullPointerException
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.ActivityThread.access$2300(ActivityThread.java:125)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.os.Handler.dispatchMessage(Handler.java:99)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.os.Looper.loop(Looper.java:123)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.ActivityThread.main(ActivityThread.java:4627)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at java.lang.reflect.Method.invokeNative(Native Method)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at java.lang.reflect.Method.invoke(Method.java:521)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at dalvik.system.NativeStart.main(Native Method)
04-26 12:39:54.355: E/AndroidRuntime(15573): Caused by: java.lang.NullPointerException
04-26 12:39:54.355: E/AndroidRuntime(15573):    at com.group.RedPanda.FinalProject.SubScreen.onCreate(SubScreen.java:29)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-26 12:39:54.355: E/AndroidRuntime(15573):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)

Answer 1

试试这个......你真正想做的事情就是这样：

@Override
public boolean onOptionsItemSelected(MenuItem menuItem) {
    switch (menuItem.getItemId()) {
    case android.R.id.home:
      Intent homeIntent = new Intent(this, HomeActivity.class);
      homeIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
      startActivity(homeIntent);
    }
  return (super.onOptionsItemSelected(menuItem));
}

这将带您进入父活动，而不只是通过后台堆栈。我还添加了Intent.Flag以清除后台堆栈，当你进入家庭活动时它是一个很有用的，当用户使用“向上”按钮时可以阻止后台陷入困境

使用操作栏中的后退按钮时出错

1 个答案: