Question

我想在异步任务onPreExecute()中显示进度条。但是我无法通过context。有人可以帮忙吗？

public class myClass extends AsyncTask<Void,Void,Void>{
    Context ctx;
    ProgressDialog d;
    String s;


    public myClass (String S, Context con) {
        this.ctx = con;
        this.s = S;
    }


    @Override
        protected void onPreExecute() {
            d = new ProgressDialog(this.ctx);
            d.setMessage("Please wait...");
            d.setIndeterminate(true);
            d.show();
        }

从主要活动中调用

 new myClass(MainActivity.this);
 myClassObj.execute(s);

Answer 1

它应该是这样的，传递给构造函数。

testProj/include

这样称呼它。

public class myClass extends AsyncTask<Void,Void,Void>{
    private ProgressDialog dialog;
    private String paramOne;
    private int paramTwo;

    public myClass (Activity activity, String paramOne, int paramTwo) {
       dialog = new ProgressDialog(activity);
       this.paramOne = paramOne; // "Hello"
       this.paramTwo = paramTwo; // 123
    }

    @Override
    protected void onPreExecute() {
       dialog.setMessage("Please wait...");
       dialog.setIndeterminate(true);
       dialog.show();
    }

Answer 2

我有更好的方法，在你的活动或片段中使用进度条，一旦你开始你的asynctask设置可见性到VISIBLE，当你在postExecute上得到结果时，通过使用活动中的界面设置可见性。像这样的东西

/**
     * Listener for listening events happening in background task, whether cancelled or completed
     * with error or success.
     */
    public interface Listener {
        /**
         * Callback invoked when request is completed and response is got with
         * code == {@value java.net.HttpURLConnection#HTTP_OK}.
         */
        void onSuccess(Response response);

        /**
         * Callback invoked when request is cancelled or completed with response
         * code != {@value java.net.HttpURLConnection#HTTP_OK}.
         */
        void onError(Response response);
    }

并在您的活动中

   void onSuccess(Response response){
       //Visibility to Gone.
   }

Answer 3

将有两种情况调用AsyncTask，在同一个Activity中调用AsyncTask时： -

public class myClass extends AsyncTask<Void,Void,Void>{
ProgressDialog d;
String s;

public myClass (String str) {
    this.s= str;
}
@Override
    protected void onPreExecute() {
        d = new ProgressDialog(getApplicatinContext());
        d.setMessage("Please wait...");
        d.setIndeterminate(true);
        d.show();
    }

从主要活动中调用

myClassObj.execute();

如果你需要在单独的Activity或单独的文件中调用，那么你需要遵循以下代码： -

public class myClass extends AsyncTask<Void,Void,Void>{
    Activity act;
    ProgressDialog d;


public myClass (Activity act) {
    this.act = act;
}


@Override
    protected void onPreExecute() {
        d = new ProgressDialog(act.getApplicationContext());
        d.setMessage("Please wait...");
        d.setIndeterminate(true);
        d.show();
    }

从主要活动中调用

new myClass(MainActivity.this);
myClassObj.execute(s);

在Android中的异步任务中显示进度条

3 个答案: