尝试在空对象引用上调用虚拟方法'android.view.View android.view.View.getRootView()' [英] Attempt to invoke virtual method 'android.view.View android.view.View.getRootView()' on a null object reference

问题描述

我收到此错误

试图调用虚拟方法'android.view.ViewNULL对象引用上的android.view.View.getRootView()'

"Attempt to invoke virtual method 'android.view.View android.view.View.getRootView()' on a null object reference"

这是我的代码.

black.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            View bView = findViewById(R.id.lin);
            View root = bView.getRootView();
            root.setBackgroundColor(Color.parseColor("#000000"));
        }
    });

我有两个视图，一个称为overlay_view，另一个称为activity_main.我正在尝试更改overlay_view的颜色，但出现此错误.我将setcontentView设置为activity_main，如果将其切换为overlay_view，则不会出现错误.但是我不想将setContentView切换为overlay_view，所以还有另一种方法吗?谢谢

I have two views, one called overlay_view and the other activity_main. I am trying to change the color of overlay_view but I am getting this error. I have the setcontentView to activity_main, and if I switch it to overlay_view it does not give me a error. However I do not want to switch the setContentView to overlay_view so is there another way to do this? Thanks

我有一个添加了overlay_view的服务.该服务是从mainactivity调用的.这是在主要活动中调用它的地方:

I have a service which adds in overlay_view. The service is called from the mainactivity. Here is where it is called from in the main activity:

    public void sendMessage(){
    Intent intent = new Intent(this, DrawOverAppsService.class);

    startService(intent);
    Intent intent1 = new Intent(this, MainActivity.class);
}

这是服务:

public class DrawOverAppsService extends Service {

public static final String TAG = "DrawOverAppsService";



View mOverlayView;

@Override
public IBinder onBind(Intent intent) {
    return null;
}

@Override
public void onCreate() {
    super.onCreate();

    Log.d(TAG, "onCreate");


    final WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            WindowManager.LayoutParams.MATCH_PARENT,
            WindowManager.LayoutParams.MATCH_PARENT,
            WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY,
            WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
                    WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL |
                    WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN |
                    WindowManager.LayoutParams.FLAG_DIM_BEHIND,
            PixelFormat.TRANSLUCENT);

    // An alpha value to apply to this entire window.
    // An alpha of 1.0 means fully opaque and 0.0 means fully transparent
    params.alpha = 0.1F;

    // When FLAG_DIM_BEHIND is set, this is the amount of dimming to apply.
    // Range is from 1.0 for completely opaque to 0.0 for no dim.
    params.dimAmount = 0.9F;

    WindowManager wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);


    LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);


    mOverlayView = inflater.inflate(R.layout.overlay_view, null);

    wm.addView(mOverlayView, params);





}

@Override
public void onDestroy() {
    super.onDestroy();

    Log.d(TAG, "onDestroy");

        WindowManager wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
        wm.removeView(mOverlayView);


}
}

这是overlay_view的xml:

This is the xml for overlay_view:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/lin"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#FF4081"
    android:orientation="vertical"></LinearLayout>

推荐答案

您的问题是，您在服务中创建了一个视图，并希望在主活动中引用该视图以更改其背景颜色.您的行 View bView = findViewById(R.id.lin )给您一个空值，因为系统无法在 activity_main . R.id.lin 确实存在于 overlay_view 中，这就是为什么在setContentView()中使用该视图时不会出现错误的原因.

Your issue is that you create a view in a service and want to reference it in the main activity to change its background color. Your line View bView = findViewById(R.id.lin) is giving you a null value because the system cannot find R.id.lin in activity_main. R.id.lin does exist in overlay_view and that is why you don't get the error with that view used in setContentView().

服务类变量 mOverlayView 具有对所需视图的引用.我不知道通过窗口管理器添加的视图的 findViewById()功能，因此您将需要在活动和服务之间实现连接.更改背景的服务代码如下所示:

The service class variable mOverlayView has a reference to the view you want. I don't know of findViewById() functionality for views added via the window manager, so you will need to implement a connection between the activity and the service. The service code to change the background will look something like this:

View bView = mOverlayView.findViewById(R.id.lin);
if (bView != null) {}
    View root = bView.getRootView();
    root.setBackgroundColor(Color.parseColor("#000000"));
}

在活动的 onClick 处理程序中，您将通知服务更改背景.有几种方法可以解决此问题，您可能已经有一种向服务发送命令的方法.如果不是，请查看 startService

In the onClick handler of the activity, you will notify the service to change the background. There are several ways to handle this and you may already have a way to send commands to the service. If not, take a look at startService

每次调用此方法都将导致对目标服务的onStartCommand(Intent，int，int)方法的相应调用，并在此给出意图.这提供了一种便捷的方式，可以将作业提交给服务，而不必绑定并调用其接口.

Every call to this method will result in a corresponding call to the target service's onStartCommand(Intent, int, int) method, with the intent given here. This provides a convenient way to submit jobs to a service without having to bind and call on to its interface.

您还可以设置本地广播管理器或绑定服务.搜索"android活动服务交流" ，以获取其他处理方式的结果.

You can also set up a local broadcast manager or bind the service. Search for "android activity service communication" for results on alternate ways to handle this.

在继续操作之前，您可能还想熟悉此问题.

You may also want to familiarize yourself with this issue before proceeding.

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