解決android應用被強殺或應用被回收導致的空指針問題

如上所示，我們新建了一個App狀態常量類用於方便統一參數，同時新建了一個AppStatus單例類，這個單例類中定義了一個int類型的參數，參數默認值為-1，也就是默認為進程關閉的狀態，而這個值是什麼時候被改變的呢，很簡單在SpalshActivity的onCreate方法被改變就可以啦！在SpalshActivity中改成正常態2即可。

public class SplashActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        AppStatusManager.getInstance().setAppStatus(AppStatusConstant.STATUS_NORMAL); //進入應用初始化設置成未登錄狀態
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_splash);
        handler.sendEmptyMessageDelayed(0, 3000);

    }

    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            startActivity(new Intent(SplashActivity.this, MainActivity.class));
            finish();
        }
    };
}

當我們的停留在某個頁面的時候應用被回收統一跳轉到MainActivity即可，因為MainActivity為SINGLETASK啟動模式，所以此時Activity棧中就只剩MainActivity一個Activity，在MainActivity中finish掉自己的同時在跳轉SplashActivity即可完成，這樣也就強制APP重新走了啟動流程，為了統一管理，我們新建一個BaseActivity，其他Activty繼承這個BaseActivity，改造後的代碼如下：

/**
 * Created by lvzishen on 2016/5/5.
 */
public abstract class BaseActivity extends AppCompatActivity {
    /**
     * @param savedInstanceState
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        switch (AppStatusManager.getInstance().getAppStatus()) {
            /**
             * 應用被強殺
             */
            case AppStatusConstant.STATUS_FORCE_KILLED:
                //跳到主頁,主頁lauchmode SINGLETASK
                protectApp();
                break;
            /**
             * 用戶被踢或者TOKEN失效
             */
            case AppStatusConstant.STATUS_KICK_OUT:
                //彈出對話框,點擊之後跳到主頁,清除用戶信息,運行退出登錄邏輯
//                Intent intent=new Intent(this,MainActivity.class);
//                startActivity(intent);
                break;
            case AppStatusConstant.STATUS_NORMAL:
                setUpContentView();
                setUpView();
                setUpData(savedInstanceState);
                break;
        }


    }

    /**
     * 加載布局
     */
    protected abstract void setUpContentView();

    /**
     * view初始化
     */
    protected abstract void setUpView();

    /**
     * 加載數據
     */
    protected abstract void setUpData(Bundle savedInstanceState);

    protected void protectApp() {
        Intent intent = new Intent(this, MainActivity.class);
        intent.putExtra(AppStatusConstant.KEY_HOME_ACTION, AppStatusConstant.ACTION_RESTART_APP);
        startActivity(intent);
    }

    @Override
    public void onBackPressed() {
        // 返回默認結束當前頁面
        finish();
    }


}

public class SplashActivity extends BaseActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        AppStatusManager.getInstance().setAppStatus(AppStatusConstant.STATUS_NORMAL); //進入應用初始化設置成未登錄狀態
        super.onCreate(savedInstanceState);

    }

    @Override
    protected void setUpContentView() {
        setContentView(R.layout.activity_splash);
    }

    @Override
    protected void setUpView() {

    }

    @Override
    protected void setUpData(Bundle savedInstanceState) {
        handler.sendEmptyMessageDelayed(0, 3000);
    }

    Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            startActivity(new Intent(SplashActivity.this, MainActivity.class));
            finish();
        }
    };
}

public class MainActivity extends BaseActivity {
    Button button;
    @Override
    protected void setUpContentView() {
        setContentView(R.layout.activity_main);
    }

    @Override
    protected void setUpView() {
        button= (Button) findViewById(R.id.activity_main_btn);
    }

    @Override
    protected void setUpData(Bundle savedInstanceState) {
        MyApplication.list=new ArrayList<>();
        MyApplication.list.add("我從MAINACTIVITY來");
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, InfoActivity.class));
            }
        });
    }


    @Override
    protected void protectApp() {
     Toast.makeText(getApplicationContext(),"應用被回收重啟走流程",Toast.LENGTH_LONG).show();
        startActivity(new Intent(this, SplashActivity.class));
        finish();
    }
    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        int action = intent.getIntExtra(AppStatusConstant.KEY_HOME_ACTION, AppStatusConstant.ACTION_BACK_TO_HOME);
        switch (action) {
            case AppStatusConstant.ACTION_RESTART_APP:
                protectApp();
                break;
            case AppStatusConstant.ACTION_KICK_OUT:
                break;
            case AppStatusConstant.ACTION_BACK_TO_HOME:
                break;
        }
    }

}

public class InfoActivity extends BaseActivity {
    TextView textView;

    @Override
    protected void setUpContentView() {
        setContentView(R.layout.activity_info);
    }

    @Override
    protected void setUpView() {
        TextView textView= (TextView) findViewById(R.id.text);
    }

    @Override
    protected void setUpData(Bundle savedInstanceState) {
        textView.setText(MyApplication.list.get(0));
    }
}