应用程序崩溃并且不显示Toast消息

Question

I am new to Android development. I want to display a Toast message when the app is not installed. When the app is not installed, for example the Facebook app, the app is crashing. What is the problem in my code?

case R.id.Facebook:
    Intent facebook = getPackageManager().getLaunchIntentForPackage("com.facebook.katana");
    startActivity(facebook);
    if (facebook != null) {
        Toast.makeText(this,"Facebook is not installed ",Toast.LENGTH_LONG);
    }
    return true;

Answer 1

You check for null too late, try this:

case R.id.Facebook:
    Intent facebook = getPackageManager().getLaunchIntentForPackage("com.facebook.katana");
    if (facebook == null) {
        Toast.makeText(this,"Facebook is not installed ",Toast.LENGTH_LONG).show();
    } else {
       startActivity(facebook);
    }
    return true;

Answer 2

要显示烤面包，您需要在烤面包对象上调用.show()