即使在使用 AsyncTask 之后，编舞者也会跳帧（最多 400 个！）

Question

我正在尝试从远程服务器获取数据，尝试在 SQLite 中创建数据库并更新我的共享首选项。我将前面提到的所有操作都放在了 AsyncTask 中，理论上它必须在 UI（主）线程之外的单独线程上运行。另外，我在实际的 Android 设备上运行该应用程序，而不是在模拟器上。

我在日志中得到以下信息：

I/Choreographer: Skipped 229 frames!  The application may be doing too much work on its main thread.

源代码：

import android.annotation.SuppressLint;
import android.content.Context;
import android.content.SharedPreferences;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteStatement;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.concurrent.ExecutionException;

public class MainActivity extends AppCompatActivity {

    TextView errorMessage;
    Button retryAgainButton;

    SharedPreferences sharedPrefs;

    @SuppressLint("StaticFieldLeak")
    public class FirstRunDBCreator extends AsyncTask<Void, Void, String> {
        String result = "";
        private Exception e = null;

        @Override
        protected void onPreExecute() {
            sharedPrefs = getApplicationContext().getSharedPreferences("android.content.SharedPreference", Context.MODE_PRIVATE);
            if(!sharedPrefs.contains("firstRun")) {
                sharedPrefs.edit().putBoolean("firstRun", true).apply();
            }
        }

        @Override
        protected String doInBackground(Void... voids) {
            String result = "";
            // All the heavy operations here
            // Fetching the data from the server here and creating/ storing data in my SQLite database
            // I have also used transactions and SQLite preparedStatement to increase the insert speed
            return result;
        }

        @SuppressLint("SetTextI18n")
        @Override
        protected void onPostExecute(String s) {
            // Closing the database connections and handling any exceptions here
            // Updating the UI elements such as diplaying the complete message or the visibility of a textview
        }
    }

    public void initializeTheUIComponents() {
        errorMessage = findViewById(R.id.errorMessage);
        retryAgainButton = findViewById(R.id.retryAgainButton);
        retryAgainButton.setClickable(false);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initializeTheUIComponents();
        // Running the jumpToNextActivity after the screen and the UI elements have been rendered
        getWindow().getDecorView().post(new Runnable() {
            @Override
            public void run() {
                try {
                    new FirstRunDBCreator().execute().get();
                } catch (InterruptedException | ExecutionException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

虽然，除了两个 TextView 和所有繁重的处理都在后台线程中执行的事实之外，我没有任何高分辨率图像或任何繁重的前端组件，是什么导致编舞者跳过帧？是因为我在onCreate() 方法中调用了AsyncTask，还是因为我在onPreExecute() 或onPostExecute()? 中有一些代码是Runnable run() 还是任何其他原因？

Answer 1

当您调用 .get() 方法时，它将在当前线程上运行，在这种情况下是 UI 线程，因此请尝试在没有 get 的情况下执行。

Answer 2

建议为 asyncTask 使用 weakReference 上下文，像这样：

 /.../in your activity
  WeakReference<Context> baseContext = new WeakReference<>(MainActivity.this);

更新了 FirstRunDBCreator 类

public class FirstRunDBCreator extends AsyncTask<Void, Void, String> {
private WeakReference<Context> context;

public FirstRunDBCreator(WeakReference<Context> context) {
    this.context = context;
}

@Override
protected String doInBackground(Void... voids) {
    Context baseContext = context.get();
    SharedPreferences sp = baseContext.getSharedPreferences("android.content.SharedPreference", Context.MODE_PRIVATE);
    if(!sp.contains("firstRun")) {
        sp.edit().putBoolean("firstRun", true).apply();
    }
    String result = "";
    //initialize DataBase from baseContext


    return result;
}

@Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    context.clear();
}

在你的活动中

  /.../
  new FirstRunDBCreator(baseContext).execute();