Dropdown android - 仅在用户更改其值时调用 setOnItemSelectedListener答案

【问题标题】：Dropdown android - call setOnItemSelectedListener only when user change its valueDropdown android - 仅在用户更改其值时调用 setOnItemSelectedListener
【发布时间】：2020-11-18 13:11:41
【问题描述】：

我有一个下拉列表，我在上面设置了一些值，并默认显示用户从共享首选项保存的最后一个值。它运作良好。问题是当我开始活动时，将这个保存的用户值放在选择上，默认情况下，它调用setOnItemSelectedListener 并向用户显示敬酒。这次我不想在 setOnItemSelectedListener 中运行块代码，就在用户更改下拉值时。有什么办法解决吗？

String defaultValue = pref02.getString("fonte", "Normal");
String[] items = new String[]{"Normal", "10", "12", "14", "16", "18", "20", "24", "28", "30"};
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, items);
dropdown.setAdapter(adapter);
int spinnerPosition = adapter.getPosition(defaultValue);
dropdown.setSelection(spinnerPosition); //select the atual saved value.
dropdown.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {
        SharedPreferences pref2 = getApplicationContext().getSharedPreferences("pref02", MODE_PRIVATE);
        SharedPreferences.Editor editor = pref2.edit();

        String drop = dropdown.getSelectedItem().toString();
        editor.putString("fonte", drop);
        editor.apply();
        Toast.makeText(Config.this, "Saved :)", Toast.LENGTH_LONG).show();
    }
    @Override
    public void onNothingSelected(AdapterView<?> parentView) {
        // your code here
    }
});

【问题讨论】：

标签： java android android-studio dropdown

【解决方案1】：

解决方案：使用以下代码（您可以查看注释行以查看指南）

String defaultValue = pref02.getString("fonte", "Normal");
String[] items = new String[]{"Normal", "10", "12", "14", "16", "18", "20", "24", "28", "30"};
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, items);
dropdown.setAdapter(adapter);
int spinnerPosition = adapter.getPosition(defaultValue);
dropdown.setSelection(spinnerPosition); //select the atual saved value.

// Add this block of code
dropdown.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
    @Override
    public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
        // Remove listener to make sure it doesn't called later.
        dropdown.removeOnLayoutChangeListener(this);

        // Set your listener here
        dropdown.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parentView, View selectedItemView, int position, long id) {
                SharedPreferences pref2 = getApplicationContext().getSharedPreferences("pref02", MODE_PRIVATE);
                SharedPreferences.Editor editor = pref2.edit();

                String drop = dropdown.getSelectedItem().toString();
                editor.putString("fonte", drop);
                editor.apply();
                Toast.makeText(Config.this, "Saved :)", Toast.LENGTH_LONG).show();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parentView) {
                // your code here
            }
        });
    }
});

【讨论】：