应用程序在启动时崩溃-“ onCreate（）之前的活动无法使用系统服务”

Question

我想检查一个应用程序是否正在使用以下代码运行。 但是，我的应用在启动时崩溃了。 我正在使用ActivityManager查找应用程序的存在。 isAppRunning方法采用应用程序的名称，如果ActivityManager认为它当前正在运行，则返回true。

package com.mavenmaverick.process;
import java.util.List;
import android.app.Activity;
import android.app.ActivityManager;
import android.app.ActivityManager.RunningAppProcessInfo;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    MainActivity M = new MainActivity();
    M.isAppRunning("com.mcent.app");

}

public boolean isAppRunning (String aApplicationPackageName)
{
        ActivityManager activityManager = (ActivityManager) this.getSystemService(ACTIVITY_SERVICE);
            if (activityManager == null)
            {       
                    Toast.makeText(this, "Not Running", Toast.LENGTH_SHORT).show();
                    return false;
            }
            List<RunningAppProcessInfo> procInfos = activityManager.getRunningAppProcesses();
            for(int idx = 0; idx < procInfos.size(); idx++)
                {
                    if(procInfos.get(idx).processName.equals(aApplicationPackageName))
                        {
                            Toast.makeText(this, "Running", Toast.LENGTH_SHORT).show();
                            return true;
                        }
                }
            return false;
}

LogCat

01-14 01:19:45.695: E/AndroidRuntime(3335): FATAL EXCEPTION: main
01-14 01:19:45.695: E/AndroidRuntime(3335): java.lang.RuntimeException: Unable to start activity       ComponentInfo{com.mavenmaverick.process/com.mavenmaverick.process.MainActivity}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.os.Looper.loop(Looper.java:137)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.ActivityThread.main(ActivityThread.java:5103)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at java.lang.reflect.Method.invokeNative(Native Method)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at java.lang.reflect.Method.invoke(Method.java:525)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at dalvik.system.NativeStart.main(Native Method)
01-14 01:19:45.695: E/AndroidRuntime(3335): Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.Activity.getSystemService(Activity.java:4492)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at com.mavenmaverick.process.MainActivity.isAppRunning(MainActivity.java:28)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at com.mavenmaverick.process.MainActivity.onCreate(MainActivity.java:22)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.Activity.performCreate(Activity.java:5133)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-14 01:19:45.695: E/AndroidRuntime(3335):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)

Answer 1

步骤1：删除MainActivity M = new MainActivity(); 。 永远不要手动创建Activity的实例（或者是Service或ContentProvider ）。

步骤2：更改M.isAppRunning("com.mcent.app"); 到isAppRunning("com.mcent.app");