Android 无法解析符号“上下文”

Cannot resolve symbol 'context'

提问by hexicle

I'm trying to write an Android app which automatically uploads a picture to a server, but I am stuck on just one line of code:

我正在尝试编写一个自动将图片上传到服务器的 Android 应用程序，但我只停留在一行代码上：

        File f = File(context.getCacheDir(), "filename");

The error I get is

我得到的错误是

This puzzles me because I see so many examples on the web of people using context.getCacheDir()just fine, whereas I get the error message. It's probably something wrong with my IDE settings. I am using IntelliJ IDE.

这让我很困惑，因为我在网上看到很多人使用context.getCacheDir()很好的例子，而我却收到了错误消息。我的IDE设置可能有问题。我正在使用 IntelliJ IDE。

Here's is the context of the context problem:

这是上下文问题的上下文：

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data)
    {
        super.onActivityResult(requestCode, resultCode, data);
        if( requestCode == CAMERA_PIC_REQUEST)
        {
            Bitmap thumbnail = (Bitmap) data.getExtras().get("data");
            ImageView image =(ImageView) findViewById(R.id.PhotoCaptured);
            image.setImageBitmap(thumbnail);

            //create a file to write bitmap data
            File f = File(context.getCacheDir(), "filename");
            try {
                f.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }

回答by Simon

You need to do some basic Java programming tutorials. Java is totally different to JavaScript.

您需要学习一些基本的 Java 编程教程。Java 与 JavaScript 完全不同。

Here, you use contextas a variable but you have neither declared it, or initialised it, hence the error.

在这里，您context用作变量，但您既没有声明它，也没有初始化它，因此出现错误。

You could define it (and initialise at the same time)

您可以定义它（并同时初始化）

 Context context = this;

since thisrefers to the current object instance of a class and Activityis a Context, or more precisely, it extendsContext.

因为this指的是类的当前对象实例，并且Activity是 a Context，或者更准确地说是 it extendsContext。

Alternatively, you could just use this.

或者，您可以只使用this.

File f = File(UploadToServer.this.getCacheDir(), "filename");

回答by dmSherazi

The error is bacuse you havent declared context, neither it has been passed as a parameter

错误是因为你没有声明context，也没有作为参数传递

change context.getCacheDir()to getApplicationContext.getCacheDir()or this.getCacheDir()

更改context.getCacheDir()为getApplicationContext.getCacheDir()或this.getCacheDir()

so

所以

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data)
{
    super.onActivityResult(requestCode, resultCode, data);
    if( requestCode == CAMERA_PIC_REQUEST)
    {
        Bitmap thumbnail = (Bitmap) data.getExtras().get("data");
        ImageView image =(ImageView) findViewById(R.id.PhotoCaptured);
        image.setImageBitmap(thumbnail);

        //create a file to write bitmap data
        File f = File(context.getCacheDir(), "filename");
        try {
            f.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

will become

会变成

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data)
{
    super.onActivityResult(requestCode, resultCode, data);
    if( requestCode == CAMERA_PIC_REQUEST)
    {
        Bitmap thumbnail = (Bitmap) data.getExtras().get("data");
        ImageView image =(ImageView) findViewById(R.id.PhotoCaptured);
        image.setImageBitmap(thumbnail);

        //create a file to write bitmap data
        File f = File(getApplicationContext.getCacheDir(), "filename");
        try {
            f.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

回答by Damo Gurcinovski

Add this :

添加这个：

Context context = this;

You need this to initialize context

你需要这个来初始化上下文

Then Alt+Enter

然后 Alt+Enter

You must assign context to this Activity

您必须为此活动分配上下文