練習(xí)心得

• AsyncTask必須要在主線程中執(zhí)行execute通孽，而且僅能被執(zhí)行一次晨汹，否則報異常
• AsyncTask里的所有方法都是系統(tǒng)回調(diào)的皆刺，不要人為調(diào)用
• 耗時任務(wù)在doInBackground方法里執(zhí)行，該方法會啟動新線程執(zhí)行讲婚，注意不要在其中更新UI赵哲，會報異常
• AsyncTask除doInBackground方法外的其它方法均是在主線程中執(zhí)行的

代碼樣例

/**
 * 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);

        /**
         * 應(yīng)用AsyncTask實(shí)線非主線程更新UI的操作
         */
        final AsyncTask<HashMap<String, String>, Integer, String> asyncTask = new AsyncTask<HashMap<String, String>, Integer, String>() {
            /**
             * 啟動新的線程執(zhí)行doInBackground代碼待德，不能在其中更新UI,可通過調(diào)用publishProgress觸發(fā)
             * 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();
                }
                // 該返回值會傳遞給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執(zhí)行后觸發(fā)該方法
             * @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執(zhí)行前觸發(fā)該方法
             */
            @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("馬上開始");


            }

            /**
             * 由publishProgress觸發(fā)調(diào)用枫夺，改方法在doInBackground中調(diào)用
             * @param values 調(diào)用publishProgress時傳遞的動態(tài)參數(shù)（動態(tài)參數(shù)只能有一個而且必須是最后一個參數(shù)）
             */
            @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()));
            }
        };
        //每個AsyncTask僅能被執(zhí)行1次将宪，而且僅能在主線程執(zhí)行
        asyncTask.execute(asynTaskParams);

        stop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                asyncTask.cancel(true);
            }
        });

    }

}

運(yùn)行日志如下：

運(yùn)行日志

執(zhí)行過程中調(diào)用asyncTask.cancel(true)，運(yùn)行日志如下：

取消執(zhí)行