Each of the popup menus should have a callback function that checks the selection of all 4 popup menus. Use a conditional statement that enables the push button when the selection of each popup menu is 1.
I assume the 'popup menu' is what Matlab calls a 'Drop down' menu.
Step 1: create a new function in the app that checks all of the dropdown menus.
From Code View > Code Browser > Functions, select the gree "+" to add this function. You must replace app.DropDown with your handles.
getValueIdx = @(h)find(strcmp(h.Items, h.Value));
idx1 = getValueIdx(app.DropDown);
idx2 = getValueIdx(app.DropDown2);
idx3 = getValueIdx(app.DropDown3);
idx4 = getValueIdx(app.DropDown4);
app.Button.Enable = 'on';
Step 2: assign a ValueChangedFcn to each drop down menu
The ValueChangedFcn for each dropdown menu should appear as below plus any other code you may already have for the callback function.
function DropDownValueChanged(app, event)
For GUIDE GUIs the 2 steps would look like this
Step 1: add this function anywhere in your GUIDE GUI m-file. Replace the handles with your handle names.
idx1 = handles.popupmenu1.Value;
idx2 = handles.popupmenu2.Value;
idx3 = handles.popupmenu3.Value;
idx4 = handles.popupmenu4.Value;
handles.pushbutton1.Enable = 'on';
Step 2: Each popup menu should have a callback function that you add from within GUIDE by right-clicking the popup menu > View Callbacks > Callback. That will add a function to your m-file if it doesn't already exist. Edit the added function so it appears as below.
function popupmenu1_Callback(hObject, eventdata, handles)