Question

我有两个事件，一个执行AsincTask，另一个取消任务。我第一次按On它工作正常，但当我关闭并再次打开时，我得到一个例外

活动开始：

    public void onClick(View view){
    System.out.println("onClick");
    mTask.execute();
    setActivityBackgroundColor(getResources().getColor(android.R.color.holo_green_light));
}

关闭活动

 public void onClick2(View view){


    System.out.println("Off");
    mTask.cancel(true);
    View view2 = this.getWindow().getDecorView();
    view2.setBackgroundColor(getResources().getColor(android.R.color.holo_red_light));

}

我第一次按On它工作正常但当我关闭并再次打开时我得到了这个例外

03-08 13:36:03.874  24510-24510/com.example.soad.sms E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.soad.sms, PID: 24510
java.lang.IllegalStateException: Could not execute method of the activity
        at android.view.View$1.onClick(View.java:3828)
        at android.view.View.performClick(View.java:4443)
        at android.view.View$PerformClick.run(View.java:18475)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5070)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at android.view.View$1.onClick(View.java:3823)

at android.view.View.performClick(View.java:4443)
        at android.view.View$PerformClick.run(View.java:18475)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5070)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.IllegalStateException: Cannot execute task: the task has already been executed (a task can be executed only once)
        at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:579)
        at android.os.AsyncTask.execute(AsyncTask.java:535)
        at com.example.soad.sms.MainActivity.onClick(MainActivity.java:21)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at android.view.View$1.onClick(View.java:3823)
        at android.view.View.performClick(View.java:4443)
        at android.view.View$PerformClick.run(View.java:18475)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5070)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
        at dalvik.system.NativeStart.main(Native Method)

完整的活动代码

    public class MainActivity extends ActionBarActivity {
              private xSend mTask = new xSend();
              boolean loop = false;
   @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    xSend mTask = new xSend();
}


public void onClick(View view){
    System.out.println("onClick");
    mTask.execute();
    setActivityBackgroundColor(getResources().getColor(android.R.color.holo_green_light));
}

public void setActivityBackgroundColor(int color) {
    View view = this.getWindow().getDecorView();
    view.setBackgroundColor(color);
}

public void onClick2(View view){


    System.out.println("Off");
    mTask.cancel(true);
    View view2 = this.getWindow().getDecorView();
    view2.setBackgroundColor(getResources().getColor(android.R.color.holo_red_light));

}
    @Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

}

Answer 1

每当你启动Asynctask时，以这种方式调用它，你的问题是你试图开始已经完成asynctask

new MyAsyncTask().execute();

Answer 2

public class MainActivity extends ActionBarActivity {

    private xSend mTask = null;

...

public void onClick(View view) {
    mTask = new xSend().execute();
    ...
}

public void onClick2(View view) {
    if (mTask != null) {
        mTask.cancel(true);
        mTask = null;
    }
    ...
}

删除xSend mTask = new xSend();中的行onCreate()并阅读https://developer.android.com/reference/android/os/AsyncTask.html

中的线程规则

ava.lang.IllegalStateException：无法执行活动的方法

2 个答案: