[移动开发]java中级——消除过期的对象引用

例1——自动管理内存的类需注意内存泄漏

如下简单的栈结构

class Stack {
    private Object[] elements = new Object[16];
    private int size = 0;

    public void push(Object e) {
        elements[size++] = e;
    }

    public Object pop() {
        return elements[--size];
    }
}

在以下代码运行后就会出现内存泄漏

Stack stack = new Stack();
stack.push(1);
stack.push(2);
stack.pop();

因为刚刚pop()弹出来的elements[1]已不能通过size寻到并使用，但是栈内部的elements仍保存其引用，而解决办法是将其引用取消并告知虚拟机进行回收，如下修改pop()

public Object pop() {
    Object result = elements[--size];
    elements[size] = null;
    return result;
}

例2——注册的回调需要取消

这在Android中比较常用，在某控件的生命周期结束时，需要将回调取消，如下在onCreate()中注册网络变化的监听事件，在onDestroy()时要取消注册

public class MainActivity extends AppCompatActivity {

    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
        networkChangeReceiver = new NetworkChangeReceiver();
        registerReceiver(networkChangeReceiver, intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver);
    }

    private class NetworkChangeReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
            if (networkInfo != null && networkInfo.isAvailable()) {
                Toast.makeText(context, "Network Available", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(context, "Network Unavailable", Toast.LENGTH_SHORT).show();

            }
        }
    }
}