Instant image updating crashes the application on Android 7.x and older versions

[wuwbobo2021]

It is caused by JNI local reference overflow: get_view_rect in internal/backends/android-activity/javahelper.rs. However, there might be more potential problems. High RAM usage might occur in some other applications on newer Android versions.

Reference: rust-mobile/android-activity#173, https://developer.android.com/training/articles/perf-jni#unsupported-featuresbackwards-compatibility. "In Android versions prior to Android 8.0, the number of local references is capped at a version-specific limit. Beginning in Android 8.0, Android supports unlimited local references."

I do know how to fix the problem, but I am not sure if the jni-min-helper crate can be introduced as a dependency of i-slint-backend-android-activity.

Test case (it crashes on Android 6.0/7.0 in a few seconds):

[package]
name = "slint-test"
version = "0.1.0"
edition = "2021"
publish = false

[dependencies]
slint = { version = "1.9.0", features = ["backend-android-activity-06"] }

[lib]
crate-type = ["cdylib"]
path = "lib.rs"

#[no_mangle]
fn android_main(app: slint::android::AndroidApp) {
    slint::android::init(app).unwrap();

    slint::slint!{
        export component MainWindow inherits Window {
            in property <image> screen_image;
            Image {
                source: screen_image;
           }
        }
    }
    
    let window = MainWindow::new().unwrap();

    let window_weak = window.as_weak();
    let timer = slint::Timer::default();
    timer.start(slint::TimerMode::Repeated, std::time::Duration::from_millis(1), move || {
        // image creation process is removed in this minimal test program
        let pixel_buffer = slint::SharedPixelBuffer::<slint::Rgba8Pixel>::new(320, 240);
        let img = slint::Image::from_rgba8_premultiplied(pixel_buffer);
        window_weak.upgrade().unwrap().set_screen_image(img);
    });

    window.run().unwrap();
}

12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115] JNI ERROR (app bug): local reference table overflow (max=512)
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115] local reference table dump:
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]   Last 10 entries (of 511):
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       510: 0x12db2b20 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       509: 0x12db2b00 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       508: 0x12db2ae0 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       507: 0x12db2ac0 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       506: 0x12db2aa0 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       505: 0x12db2a80 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       504: 0x12db2a60 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       503: 0x12db2a40 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       502: 0x12db2a20 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       501: 0x12db2a00 android.graphics.Rect
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]   Summary:
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         1 of dalvik.system.DexClassLoader
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         1 of SlintAndroidJavaHelper
12-20 21:15:43.347 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         4 of java.lang.Class (4 unique instances)
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         6 of java.lang.String (6 unique instances)
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         1 of dalvik.system.PathClassLoader
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         1 of java.io.FileOutputStream
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         1 of java.nio.DirectByteBuffer
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         1 of byte[] (16064 elements)
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]       492 of android.graphics.Rect (492 unique instances)
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115]         3 of java.io.File (3 unique instances)
12-20 21:15:43.348 24093 24107 F art     : art/runtime/indirect_reference_table.cc:115] 

Besides, the virtual keyboard always prompt out on startup, maybe calling show_or_hide_soft_input(false) for once can fix the problem; the default material Slint style on Android currently features a pink color theme, which has nothing to do with the original material design style. It means a bad first impression for some people.

PS: docs.rs failed to build slint crate documentation because api/rs/slint/docs symbolic link has been deleted (commit e45e699). Would it be fixed?

[ogoffart]

Duplicate of #7182