Asynctask 有 4 个覆盖方法 onPreExecute()
, doInBackground()
, onProgressUpdate()
, onPostExecute()
除了 onProgressUpdate
一切都在工作。
我应该怎么做才能使 onProgressUpdate() 起作用。
谁能简单解释一下onProgressUpdate()
有什么用,里面应该写什么?
最佳答案
onProgressUpdate()
用于通过该方法操作异步操作的进度。注意数据类型为 Integer
的参数。这对应于类定义中的第二个参数。可以通过调用 publishProgress()
从 doInBackground()
方法的主体内触发此回调。
示例
import android.app.Activity;
import android.content.Context;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class AsyncTaskExample extends Activity {
protected TextView _percentField;
protected Button _cancelButton;
protected InitTask _initTask;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
_percentField = (TextView) findViewById(R.id.percent_field);
_cancelButton = (Button) findViewById(R.id.cancel_button);
_cancelButton.setOnClickListener(new CancelButtonListener());
_initTask = new InitTask();
_initTask.execute(this);
}
protected class CancelButtonListener implements View.OnClickListener {
public void onClick(View v) {
_initTask.cancel(true);
}
}
/**
* sub-class of AsyncTask
*/
protected class InitTask extends AsyncTask<Context, Integer, String> {
// -- run intensive processes here
// -- notice that the datatype of the first param in the class definition matches the param passed to this
// method
// -- and that the datatype of the last param in the class definition matches the return type of this method
@Override
protected String doInBackground(Context... params) {
// -- on every iteration
// -- runs a while loop that causes the thread to sleep for 50 milliseconds
// -- publishes the progress - calls the onProgressUpdate handler defined below
// -- and increments the counter variable i by one
int i = 0;
while (i <= 50) {
try {
Thread.sleep(50);
publishProgress(i);
i++;
}
catch (Exception e) {
Log.i("makemachine", e.getMessage());
}
}
return "COMPLETE!";
}
// -- gets called just before thread begins
@Override
protected void onPreExecute() {
Log.i("makemachine", "onPreExecute()");
super.onPreExecute();
}
// -- called from the publish progress
// -- notice that the datatype of the second param gets passed to this method
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
Log.i("makemachine", "onProgressUpdate(): " + String.valueOf(values[0]));
_percentField.setText((values[0] * 2) + "%");
_percentField.setTextSize(values[0]);
}
// -- called if the cancel button is pressed
@Override
protected void onCancelled() {
super.onCancelled();
Log.i("makemachine", "onCancelled()");
_percentField.setText("Cancelled!");
_percentField.setTextColor(0xFFFF0000);
}
// -- called as soon as doInBackground method completes
// -- notice that the third param gets passed to this method
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
Log.i("makemachine", "onPostExecute(): " + result);
_percentField.setText(result);
_percentField.setTextColor(0xFF69adea);
_cancelButton.setVisibility(View.INVISIBLE);
}
}
}
关于android如何使用asynctasks进度对话框,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/6450275/