吐司不适用于参数

Question

I am self studying android projects and i am very new to android and java. i cant figure out the error, please help,

Toast.makeText(this, msg, Toast.LENGTH_LONG).show();

this gives me the error that i pasted below: The method makeText(Context, CharSequence, int) in the type Toast is not applicable for the arguments (new BleWrapperUiCallbacks.Null(){}, String, int)

when i use "context" instead of "this", there is no error. if i want to use "this" keyword means what should i do? and what is the use of "this" keyword on toast.maketext function? thanking you.

Answer 1

如果要使用this作为匿名内部类（例如OnClickListener ）中Activity的指针，则必须在this之前使用Activity名称： MyActivity.this ，用Activity的名称替换。

Answer 2

this -

Within an instance method or a constructor, this is a reference to the current object

You may use this only on object that are extending Context like Activity -

Activity extends ContextThemeWrapper The method

Toast.makeText(MainActivity.this, CharSequence, int)

in other case you should use context reference

Answer 3

You could only use this keyword if you have this code in the context of the Activity class.
All gui in android have its context -> for example Activity, so to create object like toast you need to pass an Context .
If your method, in other class than Activity Subclass is using this , pass a new parameter to your method -> Context context , and use it Like (in Activity class):
MyClass.myFunction(YourActivity.this);

Answer 4

If u want to use this keyword, u can use like this,

Toast.makeText(Classname.this, msg , Toast.LENGTH_LONG).show();

Where Classname is your android class name

Answer 5

Toast.makeText(youractivityname.this, "your message text", Toast.LENGTH_LONG).show();