onStart – 蓝天白云

今天看到这样一个面试题，遂看了下Android系统源码

发现在ActivityThread.java中的performLaunchActivity函数中有这么一段代码

                if (!r.activity.mFinished) {
                    activity.performStart();
                    r.stopped = false;
                }

if (!r.activity.mFinished) {

activity.performStart();

r.stopped = false;

}

可见，如果在onStart之前如果Activity执行了finish函数，就不会再执行onStart函数了。

示例代码如下：

import androidx.appcompat.app.AppCompatActivity;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

import static java.lang.ClassLoader.getSystemClassLoader;

public class MainActivity extends AppCompatActivity {
    private String LOG_TAG = "MainActivity";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Log.d(LOG_TAG, "onCreate");
        finish();
    }

    @Override
    protected void onStart() {
        Log.d(LOG_TAG, "onStart");
        super.onStart();
    }

}

import androidx.appcompat.app.AppCompatActivity;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import android.os.Bundle;

import android.util.Log;

import android.view.View;

import static java.lang.ClassLoader.getSystemClassLoader;

public class MainActivity extends AppCompatActivity {

private String LOG_TAG = "MainActivity";

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Log.d(LOG_TAG, "onCreate");

finish();

}

@Override

protected void onStart() {

Log.d(LOG_TAG, "onStart");

super.onStart();

}