How to trigger a function when a user goes back to a background app?

问题

For example, an user opens an app, presses the home button, and then comes back to the app again.

Is there any way to trigger certain functions when the user navigates back to the app? Such as auto load a view object when the user is back to the app.

This question is for both Android & iOS.

回答1:

Use the following to your likings in the projects's AppDelegate.m file (iOS only)

- (void)applicationWillResignActive:(UIApplication *)application
{
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}

回答2:

In onPause() method write this code to know that your application is went to background.

public void onPause()
{
 ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
Boolean flag=false;     

List<RunningTaskInfo> tasks = am.getRunningTasks(1);
        if (!tasks.isEmpty()) {
          ComponentName topActivity = tasks.get(0).topActivity;
          if (!topActivity.getPackageName().equals(context.getPackageName())) {
            flag=true;
          }
        }
if(flag)
{
//App went to background...
}

}

Use the above flag in onResume() to know that your application was resumed.

回答3:

for android you can right your code in onResume function which is called when backgroud app come to front. but remember android life cycle which is

onCreate-->onResume.

so onResume is always called even app runs first time or come from background. but onCreate called only when Activity created first time.

you can set some variable on onPause method which is called when app is going to background

and when you get that variable "true" and onResume called you can perform you task.

enjoy.

回答4:

try to use a boolean variable in Two methods of the acitivity, onKeyDown and onPause.

boolean backFromBackground = false;

onCreate(){
 //whatever you want
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {     

    if(keyCode == KeyEvent.KEYCODE_HOME)
    {

       backFromBackground = true;
    }
}
onPause(){
 if(backFromBackground){
  //do what ever you want
 }
}

来源：https://stackoverflow.com/questions/13512180/how-to-trigger-a-function-when-a-user-goes-back-to-a-background-app