Fatal编程技术网
  • android/
  • Android：类中没有活动的警报对话框

Android：类中没有活动的警报对话框

android

Android：类中没有活动的警报对话框,android,android-activity,android-alertdialog,Android,Android Activity,Android Alertdialog,我有这门课： public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> { ImageFromWeb ifw; private String url; private final WeakReference<ImageView> imageViewReference; public DownloadImageTask(ImageView imageView) { imageVi

我有这门课：

public class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {

ImageFromWeb ifw;
private String url;
private final WeakReference<ImageView> imageViewReference;

public DownloadImageTask(ImageView imageView) {
    imageViewReference = new WeakReference<ImageView>(imageView);
}

@Override
protected Bitmap doInBackground(String... params) {
    url = params[0];
    try {
        return BitmapFactory.decodeStream(new URL(url).openConnection().getInputStream());
    } catch (MalformedURLException e) {
        e.printStackTrace();
        return null;
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }
}

@Override
protected void onPostExecute(Bitmap result) {
    if (isCancelled()) {
        result = null;
    }
    if (imageViewReference != null) {
        ImageView imageView = imageViewReference.get();
        if (imageView != null) {
            imageView.setImageBitmap(result);
        }
    }
}

@Override
protected void onPreExecute() {
    if (imageViewReference != null) {
        ImageView imageView = imageViewReference.get();
        if (imageView != null) {
 ---------> imageView.setImageResource(R.drawable.pw);     
        }
    }
}
}

我想在箭头点（在DownloadImageTask类中）中放置一个警报对话框！我该怎么做？因为这门课不是一项活动

谢谢：）

更改构造函数并传递
上下文
对象

Context mContext;
public DownloadImageTask(ImageView imageView,Context mContext) {
    imageViewReference = new WeakReference<ImageView>(imageView);
    this.mContext = mContext;
}

Context-mContext；
公共下载ImageTask（ImageView、上下文mContext）{
imageViewReference=新的WeakReference（imageView）；
this.mContext=mContext；
}
现在，您可以使用此上下文创建对话框

您甚至可以将
mContext
强制转换为活动类并调用活动中的函数

更改构造函数并传递
上下文
对象

Context mContext;
public DownloadImageTask(ImageView imageView,Context mContext) {
    imageViewReference = new WeakReference<ImageView>(imageView);
    this.mContext = mContext;
}

Context-mContext；
公共下载ImageTask（ImageView、上下文mContext）{
imageViewReference=新的WeakReference（imageView）；
this.mContext=mContext；
}
现在，您可以使用此上下文创建对话框

您甚至可以将
mContext
强制转换为活动类，并调用活动中的函数

将异步任务移动到活动中，并使用该任务调用下载的ImageTask类和方法。这将使您的生活更加轻松。

将异步任务移动到您的活动中，并使用它调用您的DownloadImageTask类和方法。这将使您的生活更加轻松。

将活动实例传递给要显示对话框的类，然后检查

if(!actvity.isFinishing){
//show dialog
}
将活动实例传递给要显示对话框的类，并选中

if(!actvity.isFinishing){
//show dialog
}
您的应用程序中可以有如下静态上下文：

public static Context CurrentContext;

public abstract class CustomActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApplication.CurrentContext = this;
    }
}

AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
                    dlgBuilder.setTitle("Context Example");
                    dlgBuilder.setMessage("I am being shown from the application Static context!");
                    dlgBuilder.setNeutralButton("Ok", null);
                    dlgBuilder.show();
以及一个自定义抽象活动，该活动在创建时设置currentContext，如下所示：

public static Context CurrentContext;

public abstract class CustomActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApplication.CurrentContext = this;
    }
}

AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
                    dlgBuilder.setTitle("Context Example");
                    dlgBuilder.setMessage("I am being shown from the application Static context!");
                    dlgBuilder.setNeutralButton("Ok", null);
                    dlgBuilder.show();
然后您将获得如下上下文：

public static Context CurrentContext;

public abstract class CustomActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApplication.CurrentContext = this;
    }
}

AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
                    dlgBuilder.setTitle("Context Example");
                    dlgBuilder.setMessage("I am being shown from the application Static context!");
                    dlgBuilder.setNeutralButton("Ok", null);
                    dlgBuilder.show();
这样，无论您是在后台任务中还是直接在活动中，您都不必担心上下文。在大多数情况下，它都会起作用

希望这有帮助

应用程序中可以有如下静态上下文：

public static Context CurrentContext;

public abstract class CustomActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApplication.CurrentContext = this;
    }
}

AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
                    dlgBuilder.setTitle("Context Example");
                    dlgBuilder.setMessage("I am being shown from the application Static context!");
                    dlgBuilder.setNeutralButton("Ok", null);
                    dlgBuilder.show();
以及一个自定义抽象活动，该活动在创建时设置currentContext，如下所示：

public static Context CurrentContext;

public abstract class CustomActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApplication.CurrentContext = this;
    }
}

AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
                    dlgBuilder.setTitle("Context Example");
                    dlgBuilder.setMessage("I am being shown from the application Static context!");
                    dlgBuilder.setNeutralButton("Ok", null);
                    dlgBuilder.show();
然后您将获得如下上下文：

public static Context CurrentContext;

public abstract class CustomActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyApplication.CurrentContext = this;
    }
}

AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(MyApplication.CurrentContext);
                    dlgBuilder.setTitle("Context Example");
                    dlgBuilder.setMessage("I am being shown from the application Static context!");
                    dlgBuilder.setNeutralButton("Ok", null);
                    dlgBuilder.show();
这样，无论您是在后台任务中还是直接在活动中，您都不必担心上下文。在大多数情况下，它都会起作用

希望这有帮助

我这样做了，在“new DownloadImageTask（mChart）.execute（path）；”行中，我把这个“new DownloadImageTask（mChart，this.getApplicationContext（））.execute（path）；”！是这样吗？我在这方面有个错误！[update]我在onCreate方法中加入了“Context mContext=this；”，在“new DownloadImageTask（mChart，mContext）.execute（path）；”之后，它工作了！谢谢！我这样做了，在“new DownloadImageTask（mChart）.execute（path）；”行中，我把这个“new DownloadImageTask（mChart，this.getApplicationContext（））.execute（path）；”！是这样吗？我在这方面有个错误！[update]我在onCreate方法中加入了“Context mContext=this；”，在“new DownloadImageTask（mChart，mContext）.execute（path）；”之后，它工作了！谢谢！