java - Android-打开已创建的 Activity

我有问题我有两个 Activity -MainActivity和ActivityB

一个。第一个 Activity (MainActivity)具有一个启动ActivityB的按钮

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                Intent activityB = new Intent(MainActivity.this, activityB.class);
                startActivity(activityB);
            }
        });

b。第二 Activity 没有几个文本字段

当我在ActivityB中单击后退按钮时，应用程序切换到MainActivity，但我没有完成()ActivityB。

我如何编程MainActivity上的按钮，它将检查是否已创建ActivityB。如果是，则仅切换到ActivityB(也许在文本字段中输入一些键入的数据)，否则创建ActivityB并切换到它？

此时，每次单击按钮都会创建新的 Activity (新的文本字段等，因此用户在数据之前会先写一些)。

我试过了

android:launchMode="singleInstance"

并标记FLAG_ACTIVITY_REORDER_TO_FRONT ...

最佳答案

ActivityA-> ActivityB-> ActivityA(重复使用)

在启动ActivityA时在ActivityB中:

使用标志:

    /**
     * When an existing singleTask activity is launched,
     * all other activities above it in the stack will be destroyed.
     * It's different when launchMode is "Standard".
     * The task which contains flag will come to the foreground
     * and keep the state the same as before.
     * When you press HOME and launch the activity again,
     * ActivityManger calls an intent
     *     {act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER]
     *      flag=FLAG_ACTIVITY_NEW_TASK|FLAG_ACTIVITY_RESET_IF_NEEDED cmp=A}
     */

 Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_SINGLE_TOP;

设置演员或动作

并在ActivityA中覆盖:

  /**
 * This is called for activities that set launchMode to "singleTop" in
 * their package, or if a client used the {@link Intent#FLAG_ACTIVITY_SINGLE_TOP}
 * flag when calling {@link #startActivity}.  In either case, when the
 * activity is re-launched while at the top of the activity stack instead
 * of a new instance of the activity being started, onNewIntent() will be
 * called on the existing instance with the Intent that was used to
 * re-launch it.
 *
 * <p>An activity will always be paused before receiving a new intent, so
 * you can count on {@link #onResume} being called after this method.
 *
 * <p>Note that {@link #getIntent} still returns the original Intent.  You
 * can use {@link #setIntent} to update it to this new Intent.
 *
 * @param intent The new intent that was started for the activity.
 *
 * @see #getIntent
 * @see #setIntent
 * @see #onResume
 */
@Override
protected void onNewIntent(Intent intent) {
    super.onNewIntent(intent);
    setIntent(intent);
    /** when we are back check here intent action for example or extras  */
}

那不是我的意思。请再读一遍:如何对MainActivity上的按钮进行编程，它将检查是否已创建ActivityB。如果是，则仅切换到ActivityB(也许在文本字段中输入一些键入的数据)，否则创建ActivityB并切换到它？ -朱利叶斯·哈吉达基(Juliusz Hajdacki)

@ juliusz-hajdacki是的，这正是您想要的:)

第一个 Activity ，带有按钮

按钮侦听器以标志

开始 Activity

检查第二个 Activity

中的onNewIntent方法是否被击中或onCreate

返回结果到第一个 Activity (通过带有附加功能的开始 Activity )

请再仔细阅读一次时间:)

关于java - Android-打开已创建的 Activity ，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/34687808/