Attempt to invoke virtual method 'void android.support.v7.app.ActionBar.setHomeButtonEnabled(boolean)' on a null object reference

【Android】getActionBar()为null的解决方法总结

setContentView(R.layout.activity_main);
android.support.v7.app.ActionBar actionBar = getSupportActionBar();
actionBar.setHomeButtonEnabled(true);
actionBar.setDisplayShowHomeEnabled(true);
actionBar.setIcon(R.mipmap.ic_launcher_finish);   

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.qindou.currenciesnc/com.qindou.currenciesnc.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method ‘void android.support.v7.app.ActionBar.setHomeButtonEnabled(boolean)‘ on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper

这个又是版本的问题吗？山高路远坑深啊！