练习心得
- AsyncTask必须要在主线程中执行execute，而且仅能被执行一次，否则报异常
- AsyncTask里的所有方法都是系统回调的，不要人为调用
- 耗时任务在doInBackground方法里执行，该方法会启动新线程执行，注意不要在其中更新UI，会报异常
- AsyncTask除doInBackground方法外的其它方法均是在主线程中执行的
代码样例
/**
* Created by Rambo
*/
public class MyActivity extends MainActivity {
private EditText myEditText = null;
private Button stop = null;
private HashMap<String, String> asynTaskParams = new HashMap<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
myEditText = (EditText) findViewById(R.id.myEditText);
stop = (Button) findViewById(R.id.stop);
/**
* 应用AsyncTask实线非主线程更新UI的操作
*/
final AsyncTask<HashMap<String, String>, Integer, String> asyncTask = new AsyncTask<HashMap<String, String>, Integer, String>() {
/**
* 启动新的线程执行doInBackground代码，不能在其中更新UI,可通过调用publishProgress触发
* onProgressUpdate方法并在其中更新UI
* @param hashMaps
* @return
*/
@Override
protected String doInBackground(HashMap<String, String>... hashMaps) {
Log.v(TAG, "doInBackground thread:" + Thread.currentThread().getName());
try {
for (int index = 0; index < 5; index++) {
Thread.sleep(1000);
publishProgress(new Integer(index));
}
} catch (Exception e) {
e.printStackTrace();
}
// 该返回值会传递给onPostExecute、onCancelled(String s)
return "finish";
}
/**
*
*/
@Override
protected void onCancelled() {
super.onCancelled();
Log.v(TAG, "onCancelled() onCancelled!");
Log.v(TAG, "onCancelled() thread:" + Thread.currentThread().getName());
}
@Override
protected void onCancelled(String s) {
super.onCancelled(s);
Log.v(TAG, "onCancelled(String s) onCancelled!");
Log.v(TAG, "onCancelled " + s);
Log.v(TAG, "onCancelled(String s) thread:" + Thread.currentThread().getName());
}
/**
* doInBackground执行后触发该方法
* @param s doInBackground方法的返回值
*/
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
Log.v(TAG, "onPostExecute onPostExecute!");
Log.v(TAG, "onPostExecute " + s);
Log.v(TAG, "onPostExecute thread:" + Thread.currentThread().getName());
}
/**
* doInBackground执行前触发该方法
*/
@Override
protected void onPreExecute() {
Log.v(TAG, "onPreExecute running!");
Log.v(TAG, "onPreExecute thread:" + Thread.currentThread().getName());
asynTaskParams.put("param1", "param1");
asynTaskParams.put("param2", "param2");
asynTaskParams.put("param3", "param3");
myEditText.setText("马上开始");
}
/**
* 由publishProgress触发调用，改方法在doInBackground中调用
* @param values 调用publishProgress时传递的动态参数（动态参数只能有一个而且必须是最后一个参数）
*/
@Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
Log.v(TAG, "onProgressUpdate running!");
Log.v(TAG, "onProgressUpdate thread:" + Thread.currentThread().getName());
myEditText.setText(Integer.toString(values[0].intValue()));
}
};
//每个AsyncTask仅能被执行1次，而且仅能在主线程执行
asyncTask.execute(asynTaskParams);
stop.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
asyncTask.cancel(true);
}
});
}
}
运行日志如下：
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运行日志
运行日志
执行过程中调用asyncTask.cancel(true)，运行日志如下：
取消执行
