从线程调用 Handler 会导致 NullPointerException

发布于 2024-11-28 08:26:04 字数 1300 浏览 2 评论 0原文

我需要从 Thread 调用 Handler，这是我的 Thread：

new Thread(){
    public void run(){
        try{
            Thread.sleep(2000); 
        }
        catch(Exception ex){}

        actHandler.sendEmptyMessage(0);
    }}.start();

我像这样调用 Handler有时

actHandler=new Handler(){
    public void handleMessage(android.os.Message msg){

    }
};

它工作正常，有时它会导致该行出现 NullPointerException actHandler.sendEmptyMessage(0);

这是我的所有代码：

public class Casinos extends Activity {
    ProgressDialog pd;
    Handler actHandler;

    @Override
    public void onCreate(Bundle bundle){
        super.onCreate(bundle);
        pd=ProgressDialog.show(this,"","Please wait...");
        new Thread(){
            public void run(){
            try{
                Thread.sleep(2000); 
            }
            catch(Exception ex){}

            actHandler.sendEmptyMessage(0);
        }}.start();

        setContentView(R.layout.casinos);

        actHandler = new Handler(){
        public void handleMessage(android.os.Message msg){
            super.handleMessage(msg);
                pd.dismiss();
        }};

    }

}

该怎么办？

提前致谢。

原文

I need to call the Handler from a Thread, Here is my Thread:

new Thread(){
    public void run(){
        try{
            Thread.sleep(2000); 
        }
        catch(Exception ex){}

        actHandler.sendEmptyMessage(0);
    }}.start();

I'm calling the Handler like this

actHandler=new Handler(){
    public void handleMessage(android.os.Message msg){

    }
};

Some times its working fine and some times it leads to a NullPointerException at the line
actHandler.sendEmptyMessage(0);

Here is all my code:

public class Casinos extends Activity {
    ProgressDialog pd;
    Handler actHandler;

    @Override
    public void onCreate(Bundle bundle){
        super.onCreate(bundle);
        pd=ProgressDialog.show(this,"","Please wait...");
        new Thread(){
            public void run(){
            try{
                Thread.sleep(2000); 
            }
            catch(Exception ex){}

            actHandler.sendEmptyMessage(0);
        }}.start();

        setContentView(R.layout.casinos);

        actHandler = new Handler(){
        public void handleMessage(android.os.Message msg){
            super.handleMessage(msg);
                pd.dismiss();
        }};

    }

}

What to do?

Thanks in advance.

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

源来凯始玺欢你 2024-12-05 08:26:04

尝试这样：

Message msg = new Message();
msg.arg1 = int value;
actHandler.sendMessage(msg);

在您的情况下，如果处理消息队列的循环器正在退出，那么它将返回失败。

try like this:

Message msg = new Message();
msg.arg1 = int value;
actHandler.sendMessage(msg);

In your case if the looper processing the messsage queue is exiting then it will return failure.

回复收藏 0 原文

雨夜星沙 2024-12-05 08:26:04

您可能在 new Thread() 语句之后实例化了 actHandler。

actHandler = new Handler();

请向我们展示更多代码来验证，但情况可能就是这样。

解决方案

您已在线程声明后初始化了actHandler

public class Casinos extends Activity {
    ProgressDialog pd;
    Handler actHandler;
    @Override
    public void onCreate(Bundle bundle){
        super.onCreate(bundle);
        pd=ProgressDialog.show(this,"","Please wait...");
        //move this HERE!!
        actHandler=new Handler(){
            public void handleMessage(android.os.Message msg)
            {
                super.handleMessage(msg);
                pd.dismiss();
            }
        };

        new Thread(){
            public void run(){
                try{
                    Thread.sleep(2000); 
                }
                catch(Exception ex){}
                actHandler.sendEmptyMessage(0);
            }
        }.start();
        setContentView(R.layout.casinos);
    }
}

You may have instantiated actHandler after the new Thread() statement.

actHandler = new Handler();

Please show us some more code to verify but this is probably the case.

SOLUTION

You have initialised actHandler after the Thread declaration

public class Casinos extends Activity {
    ProgressDialog pd;
    Handler actHandler;
    @Override
    public void onCreate(Bundle bundle){
        super.onCreate(bundle);
        pd=ProgressDialog.show(this,"","Please wait...");
        //move this HERE!!
        actHandler=new Handler(){
            public void handleMessage(android.os.Message msg)
            {
                super.handleMessage(msg);
                pd.dismiss();
            }
        };

        new Thread(){
            public void run(){
                try{
                    Thread.sleep(2000); 
                }
                catch(Exception ex){}
                actHandler.sendEmptyMessage(0);
            }
        }.start();
        setContentView(R.layout.casinos);
    }
}

回复收藏 0 原文