android 判断app处于前后台

判断

onActivityResumed() 方法表示进入了前台
onActivityStopped() 方法表示进入了后台

实现方式:

在application中利用接口实现

   registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                Log.d(TAG, "onActivityCreated");
            }

            @Override
            public void onActivityStarted(Activity activity) {
                Log.d(TAG, "onActivityStarted");
                mActivityCount++;
            }

            @Override
            public void onActivityResumed(Activity activity) {
                Log.d(TAG, "onActivityResumed");
            }

            @Override
            public void onActivityPaused(Activity activity) {
                Log.d(TAG, "onActivityPaused");
            }

            @Override
            public void onActivityStopped(Activity activity) {
                Log.d(TAG, "onActivityStopped");
                mActivityCount--;
            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
                Log.d(TAG, "onActivitySaveInstanceState");
            }

            @Override
            public void onActivityDestroyed(Activity activity) {
                Log.d(TAG, "onActivityDestroyed");
            }
        });

完整代码

import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import android.util.Log;
public class TestActivityLifecycleApplcation extends Application {
    
    private final String TAG = "TestActivityLifecycle";
    private static TestActivityLifecycleApplcation mApplcation;
    private int mActivityCount = 0;

    @Override
    public void onCreate() {
        super.onCreate();
        mApplcation = new TestActivityLifecycleApplcation();

        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                Log.d(TAG, "onActivityCreated");
            }

            @Override
            public void onActivityStarted(Activity activity) {
                Log.d(TAG, "onActivityStarted");
                mActivityCount++;
            }

            @Override
            public void onActivityResumed(Activity activity) {
                Log.d(TAG, "onActivityResumed");
            }

            @Override
            public void onActivityPaused(Activity activity) {
                Log.d(TAG, "onActivityPaused");
            }

            @Override
            public void onActivityStopped(Activity activity) {
                Log.d(TAG, "onActivityStopped");
                mActivityCount--;
            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
                Log.d(TAG, "onActivitySaveInstanceState");
            }

            @Override
            public void onActivityDestroyed(Activity activity) {
                Log.d(TAG, "onActivityDestroyed");
            }
        });
    }

    public static TestActivityLifecycleApplcation getInstance() {
        if (null == mApplcation)
            mApplcation = new TestActivityLifecycleApplcation();
        return mApplcation;
    }

    public int getActivityCount() {
        return mActivityCount;
    }
}